@article{52700, abstract = {{We explore the polarization hysteretic behaviour and field-dependent permittivity of ferroelectric-dielectric 2D materials formed by random dispersions of low permittivity inclusions in a ferroelectric matrix, using finite element simulations. We show how the degree of impenetrability of dielectric inclusions plays a substantial role in controlling the coercive field, remnant and saturation polarizations of the homogenized materials. The results highlight the significance of the degree of impenetrability of inclusion in tuning the effective polarization properties of such ferroelectric composites: coercive field drops significantly as percolation threshold is attained and remnant polarization decreases faster than a linear decay.}}, author = {{Myroshnychenko, Viktor and Mulavarickal Jose, Pious Mathews and Farheen, Henna and Ejaz, Shafaq and Brosseau, Christian and Förstner, Jens}}, issn = {{0031-8949}}, journal = {{Physica Scripta}}, keywords = {{tet_topic_ferro}}, number = {{4}}, pages = {{045952}}, publisher = {{IOP Publishing}}, title = {{{From Swiss-cheese to discrete ferroelectric composites: assessing the ferroelectric butterfly shape in polarization loops}}}, doi = {{10.1088/1402-4896/ad3172}}, volume = {{99}}, year = {{2024}}, } @article{43018, author = {{Alhaddad, Samer and Förstner, Jens and Grynko, Yevgen}}, issn = {{0022-4073}}, journal = {{Journal of Quantitative Spectroscopy and Radiative Transfer}}, keywords = {{tet_topic_scattering}}, publisher = {{Elsevier BV}}, title = {{{Numerical study of light backscattering from layers of absorbing irregular particles larger than the wavelength}}}, doi = {{10.1016/j.jqsrt.2023.108557}}, volume = {{302}}, year = {{2023}}, } @inproceedings{43051, abstract = {{We demonstrate the numerical and experimental realization of optimized optical traveling-wave antennas made of low-loss dielectric materials. These antennas exhibit highly directive radiation patterns and our studies reveal that this nature comes from two dominant guided TE modes excited in the waveguide-like director of the antenna, in addition to the leaky modes. The optimized antennas possess a broadband nature and have a nearunity radiation efficiency at an operational wavelength of 780 nm. Compared to the previously studied plasmonic antennas for photon emission, our all-dielectric approach demonstrates a new class of highly directional, low-loss, and broadband optical antennas.}}, author = {{Farheen, Henna and Yan, Lok-Yee and Leuteritz, Till and Qiao, Siqi and Spreyer, Florian and Schlickriede, Christian and Quiring, Viktor and Eigner, Christof and Silberhorn, Christine and Zentgraf, Thomas and Linden, Stefan and Myroshnychenko, Viktor and Förstner, Jens}}, booktitle = {{Integrated Optics: Devices, Materials, and Technologies XXVII}}, editor = {{García-Blanco, Sonia M. and Cheben, Pavel}}, keywords = {{tet_topic_opticalantenna}}, pages = {{124241E}}, publisher = {{SPIE}}, title = {{{Tailoring the directive nature of optical waveguide antennas}}}, doi = {{10.1117/12.2658921}}, year = {{2023}}, } @inproceedings{43052, abstract = {{We demonstrate a large-scale two dimensional silicon-based optical phased array (OPA) composed of nanoantennas with circular gratings that are balanced in power and aligned in phase, required for producing desired radiation patterns in the far-field. The OPAs are numerically optimized to have an upward efficiency of up to 90%, targeting radiation concentration mainly in the field of view. We envision that our OPAs have the ability of generating complex holographic images, rendering them an attractive candidate for a wide range of applications like LiDAR sensors, optical trapping, optogenetic stimulation and augmented-reality displays.}}, author = {{Farheen, Henna and Strauch, Andreas and Scheytt, J. Christoph and Myroshnychenko, Viktor and Förstner, Jens}}, booktitle = {{Integrated Optics: Devices, Materials, and Technologies XXVII}}, editor = {{García-Blanco, Sonia M. and Cheben, Pavel}}, keywords = {{tet_topic_opticalantenna}}, pages = {{124241D }}, publisher = {{SPIE}}, title = {{{Optimized silicon antennas for optical phased arrays}}}, doi = {{10.1117/12.2658716}}, year = {{2023}}, } @article{43245, abstract = {{High-contrast slab waveguide Bragg gratings with 1D periodicity are investigated. For specific oblique excitation by semi-guided waves at sufficiently high angles of incidence, the idealized structures do not exhibit any radiative losses, such that reflectance and transmittance for the single port mode add strictly up to one. We consider a series of symmetric, fully and partly etched finite gratings, for parameters found in integrated silicon photonics. These can act as spectral filters with a reasonably flattop response. Apodization can lead to more box shaped reflectance and transmittance spectra. Together with a narrowband Fabry–Perot filter, these configurations are characterized by reflection bands, or transmittance peaks, with widths that span three orders of magnitude.}}, author = {{Hammer, Manfred and Farheen, Henna and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguide}}, number = {{4}}, pages = {{862}}, publisher = {{Optica Publishing Group}}, title = {{{How to suppress radiative losses in high-contrast integrated Bragg gratings}}}, doi = {{10.1364/josab.485725}}, volume = {{40}}, year = {{2023}}, } @article{44097, abstract = {{We present strong enhancement of third harmonic generation in an amorphous silicon metasurface consisting of elliptical nano resonators. We show that this enhancement originates from a new type of multi-mode Fano mechanism. These ‘Super-Fano’ resonances are investigated numerically in great detail using full-wave simulations. The theoretically predicted behavior of the metasurface is experimentally verified by linear and nonlinear transmission spectroscopy. Moreover, quantitative nonlinear measurements are performed, in which an absolute conversion efficiency as high as ηmax ≈ 2.8 × 10−7 a peak power intensity of 1.2 GW cm−2 is found. Compared to an unpatterned silicon film of the same thickness amplification factors of up to ~900 are demonstrated. Our results pave the way to exploiting a strong Fano-type multi-mode coupling in metasurfaces for high THG in potential applications.}}, author = {{Hähnel, David and Golla, Christian and Albert, Maximilian and Zentgraf, Thomas and Myroshnychenko, Viktor and Förstner, Jens and Meier, Cedrik}}, issn = {{2047-7538}}, journal = {{Light: Science & Applications}}, keywords = {{tet_topic_meta}}, number = {{1}}, pages = {{97}}, publisher = {{Springer Nature}}, title = {{{A multi-mode super-fano mechanism for enhanced third harmonic generation in silicon metasurfaces}}}, doi = {{https://doi.org/10.1038/s41377-023-01134-1}}, volume = {{12}}, year = {{2023}}, } @article{45596, abstract = {{Dielectric metasurfaces provide a unique platform for efficient harmonic generation and optical wavefront manipulation at the nanoscale. Tailoring phase and amplitude of a nonlinearly generated wave with a high emission efficiency using resonance-based metasurfaces is a challenging task that often requires state-of-the-art numerical methods. Here, we propose a simple yet effective approach combining a sampling method with a Monte Carlo approach to design the third-harmonic wavefront generated by all-dielectric metasurfaces composed of elliptical silicon nanodisks. Using this approach, we theoretically demonstrate the full nonlinear 2π phase control with a uniform and highest possible amplitude in the considered parameter space, allowing us to design metasurfaces operating as third harmonic beam deflectors capable of steering light into a desired direction with high emission efficiency. The TH beam deflection with a record calculated average conversion efficiency of 1.2 × 10–1 W–2 is achieved. We anticipate that the proposed approach will be widely applied as alternative to commonly used optimization algorithms with higher complexity and implementation effort for the design of metasurfaces with other holographic functionalities.}}, author = {{Hähnel, David and Förstner, Jens and Myroshnychenko, Viktor}}, issn = {{2330-4022}}, journal = {{ACS Photonics}}, keywords = {{tet_topic_meta}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Efficient Modeling and Tailoring of Nonlinear Wavefronts in Dielectric Metasurfaces}}}, doi = {{10.1021/acsphotonics.2c01967}}, year = {{2023}}, } @article{50012, abstract = {{Silicon photonics, in conjunction with complementary metal-oxide-semiconductor (CMOS) fabrication, has greatly enhanced the development of integrated optical phased arrays. This facilitates a dynamic control of light in a compact form factor that enables the synthesis of arbitrary complex wavefronts in the infrared spectrum. We numerically demonstrate a large-scale two-dimensional silicon-based optical phased array (OPA) composed of nanoantennas with circular gratings that are balanced in power and aligned in phase, required for producing elegant radiation patterns in the far-field. For a wavelength of 1.55 μm, we optimize two antennas for the OPA exhibiting an upward radiation efficiency as high as 90%, with almost 6.8% of optical power concentrated in the field of view. Additionally, we believe that the proposed OPAs can be easily fabricated and would have the ability to generate complex holographic images, rendering them an attractive candidate for a wide range of applications like LiDAR sensors, optical trapping, optogenetic stimulation, and augmented-reality displays.}}, author = {{Farheen, Henna and Strauch, Andreas and Scheytt, J. Christoph and Myroshnychenko, Viktor and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_opticalantenna}}, pages = {{101207}}, publisher = {{Elsevier BV}}, title = {{{Optimized, Highly Efficient Silicon Antennas for Optical Phased Arrays}}}, doi = {{10.1016/j.photonics.2023.101207}}, volume = {{58}}, year = {{2023}}, } @inproceedings{49890, abstract = {{In this paper, the influence of the environment on an inductive location system is analyzed. In the inductive location method, high frequency magnetic fields generated by planar coils lead to induction in other coils, which is used for localization analysis. Magnetic fields are not affected by changes in the dielectric properties of the environment, which is an advantage over other localization methods. However, electrical material parameters can still affect the localization results by indirect effects. For this reason, in this publication the influence will be investigated using real material parameters and their effects on the localization will be considered, so that the robustness and the limits of the inductive localization can be evaluated.}}, author = {{Lange, Sven and Hilleringmann, Ulrich and Hedayat, Christian and Kuhn, Harald and Förstner, Jens}}, booktitle = {{2023 IEEE Conference on Antenna Measurements and Applications (CAMA)}}, keywords = {{Planar coils, inductive locating, magnetic fields, environmental influences, eddy currents, tet_topic_hf}}, location = {{Genoa, Italy }}, publisher = {{IEEE}}, title = {{{Characterization of Various Environmental Influences on the Inductive Localization}}}, doi = {{10.1109/cama57522.2023.10352780}}, year = {{2023}}, } @article{48599, abstract = {{AbstractThe biexciton‐exciton emission cascade commonly used in quantum‐dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work, it focuses on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishability. It achieves this goal by selectively reducing the biexciton lifetime with an optical resonator. It demonstrates that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and twofold degenerate optical modes. The in‐depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum‐dot cavity excitation dynamics with full access to photon properties. It reports non‐trivial dependencies on system parameters and use the predictive power of the combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values, here specifically for the telecom C‐band at 1550 nm.}}, author = {{Bauch, David and Siebert, Dustin and Jöns, Klaus and Förstner, Jens and Schumacher, Stefan}}, issn = {{2511-9044}}, journal = {{Advanced Quantum Technologies}}, keywords = {{tet_topic_qd}}, publisher = {{Wiley}}, title = {{{On‐Demand Indistinguishable and Entangled Photons Using Tailored Cavity Designs}}}, doi = {{10.1002/qute.202300142}}, year = {{2023}}, } @unpublished{43246, abstract = {{The biexciton-exciton emission cascade commonly used in quantum-dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work we focus on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishibility. We achieve this goal by selectively reducing the biexciton lifetime with an optical resonator. We demonstrate that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and two-fold degenerate optical modes. Our in-depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum-dot cavity excitation dynamics with full access to photon properties. We report non-trivial dependencies on system parameters and use the predictive power of our combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values in the telecom C-band at $1550\,\mathrm{nm}$.}}, author = {{Bauch, David and Siebert, Dustin and Jöns, Klaus and Förstner, Jens and Schumacher, Stefan}}, keywords = {{tet_topic_phc, tet_topic_qd}}, title = {{{On-demand indistinguishable and entangled photons at telecom frequencies using tailored cavity designs}}}, year = {{2023}}, } @article{28413, abstract = {{Optical traveling wave antennas offer unique opportunities to control and selectively guide light into a specific direction, which renders them excellent candidates for optical communication and sensing. These applications require state-of-the-art engineering to reach optimized functionalities such as high directivity and radiation efficiency, low sidelobe levels, broadband and tunable capabilities, and compact design. In this work, we report on the numerical optimization of the directivity of optical traveling wave antennas made from low-loss dielectric materials using full-wave numerical simulations in conjunction with the particle swarm optimization algorithm. The antennas are composed of a reflector and a director deposited on a glass substrate, and an emitter placed in the feed gap between them serves as an internal source of excitation. In particular, we analyze antennas with rectangular- and horn-shaped directors made of either hafnium dioxide or silicon. The optimized antennas produce highly directional emissions due to the presence of two dominant guided TE modes in the director in addition to leaky modes. These guided modes dominate the far-field emission pattern and govern the direction of the main lobe emission, which predominately originates from the end facet of the director. Our work also provides a comprehensive analysis of the modes, radiation patterns, parametric influences, and bandwidths of the antennas, which highlights their robust nature.}}, author = {{Farheen, Henna and Leuteritz, Till and Linden, Stefan and Myroshnychenko, Viktor and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_opticalantenna}}, number = {{1}}, pages = {{83}}, title = {{{Optimization of optical waveguide antennas for directive emission of light}}}, doi = {{10.1364/josab.438514}}, volume = {{39}}, year = {{2022}}, } @article{29075, abstract = {{We study a double-scattering coherent mechanism of negative polarization (NP) near opposition that is observed for powder-like surfaces. The problem is solved numerically for absorbing structures with irregular constituents, cubes, spheres, and ellipsoids larger than the wavelength of incident light. Our simulations show that double scattering between two random irregular particles shows weak NP. Adding one more particle significantly increases the relative contribution of double scattering which enhances NP. Simulations with regular shapes and controlled geometric parameters show that the interference mechanism is sensitive to the geometry of the scattering system and can also result in no polarization or even strong enhancement of positive polarization at backscattering.}}, author = {{Alhaddad, Samer and Grynko, Yevgen and Farheen, Henna and Förstner, Jens}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{tet_topic_scattering}}, number = {{1}}, pages = {{58}}, title = {{{Numerical analysis of the coherent mechanism producing negative polarization at backscattering from systems of absorbing particles}}}, doi = {{10.1364/ol.444953}}, volume = {{47}}, year = {{2022}}, } @inproceedings{30387, abstract = {{Resonant evanescent coupling can be utilized to selectively excite orbital angular momentum (OAM) modes of high angular order supported by a thin circular dielectric rod. Our 2.5-D hybrid-analytical coupled mode model combines the vectorial fields associated with the fundamental TE- and TM-modes of a standard silicon photonics slab waveguide, propagating at oblique angles with respect to the rod axis, and the hybrid modes supported by the rod. One observes an efficient resonant interaction in cases where the common axial wavenumber of the waves in the slab matches the propagation constant of one or more modes of the rod. For certain modes of high angular order, the incident wave is able to transfer its directionality to the field in the fiber, exciting effectively only one of a pair of degenerate OAM modes}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, booktitle = {{Complex Light and Optical Forces XVI}}, editor = {{Andrews, David L. and Galvez, Enrique J. and Rubinsztein-Dunlop, Halina}}, keywords = {{tet_topic_waveguide}}, pages = {{120170F}}, publisher = {{SPIE}}, title = {{{Resonant evanescent excitation of OAM modes in a high-contrast circular step-index fiber}}}, doi = {{10.1117/12.2612179}}, year = {{2022}}, } @phdthesis{30722, abstract = {{In dieser Arbeit wird die elektromagnetische Wellenausbreitung in integrierten optischen Wellenleitern mit Hilfe von halb analytischen und numerischen Simulationsmethoden untersucht. Im ersten Teil werden 2-D Si/SiO2-Wellenleiterkonfigurationen mit hohem Brechungsindexkontrast betrachtet. Die Strukturen werden mit halb geführten Wellen unter schrägen Ausbreitungswinkeln angeregt. Dadurch kann die Leistungsübertragung zu bestimmten ausgehenden Moden unterdrückt werden, wodurch vollständig verlustfreie Systeme entstehen. Zusätzlich dient die Anregung mit einem seitlich begrenzten, einfallenden Wellenbündel aus halb geführten Wellen dazu, praktisch relevantere 3-D Konfigurationen zu realisieren. Darüber hinaus wird eine schrittweise Winkelspektrum-Methode vorgestellt, die es ermöglicht, in Kombination mit voll vektoriellen 2-D Finite-Elemente-Lösungen für Teilprobleme mit geringerer Komplexität, die Wellenausbreitung in planaren, linsenförmigen Wellenleitern numerisch in drei Raumrichtungen zu berechnen. Im zweiten Teil dieser Arbeit wird die Ausbreitung in Wellenleiterstrukturen aus Lithiumniobat untersucht, welche für quantenoptische Effekte genutzt werden. Zur Detektion einzelner Photonen werden supraleitende Nanodrähte auf eindiffundierten Lithiumniobat Wellenleitern mit zusätzlicher Taperschicht aus Silizium betrachtet. Um die Wellenausbreitung in diesen 3-D Wellenleitern zu beschreiben, wird eine einseitig gerichtete Finite-Elemente „Modal Matching“ Methode eingeführt. Abschließend werden Rippenwellenleiter aus Lithiumniobat analysiert, die auf Siliziumdioxid Plattformen aufgebracht sind. Der Schwerpunkt liegt hier auf dem nichtlinearen „Parametric Down-Conversion“ Prozess, der für die Erzeugung verschränkter Photonen verwendet wird.}}, author = {{Ebers, Lena}}, keywords = {{tet_topic_waveguide}}, title = {{{Semi-guided waves in integrated optical waveguide structures}}}, doi = {{10.17619/UNIPB/1-1288}}, year = {{2022}}, } @inproceedings{34136, author = {{Grynko, Yevgen and Shkuratov, Yuriy and Alhaddad, Samer and Förstner, Jens}}, keywords = {{tet_topic_scattering}}, location = {{Granada, Spain}}, publisher = {{Copernicus GmbH}}, title = {{{Light backscattering from numerical analog of planetary regoliths}}}, doi = {{ 10.5194/epsc2022-151}}, year = {{2022}}, } @article{31329, abstract = {{Highly directive antennas with the ability of shaping radiation patterns in desired directions are essential for efficient on-chip optical communication with reduced cross talk. In this paper, we design and optimize three distinct broadband traveling-wave tantalum pentoxide antennas exhibiting highly directional characteristics. Our antennas contain a director and reflector deposited on a glass substrate, which are excited by a dipole emitter placed in the feed gap between the two elements. Full-wave simulations in conjunction with global optimization provide structures with an enhanced linear directivity as high as 119 radiating in the substrate. The high directivity is a result of the interplay between two dominant TE modes and the leaky modes present in the antenna director. Furthermore, these low-loss dielectric antennas exhibit a near-unity radiation efficiency at the operational wavelength of 780 nm and maintain a broad bandwidth. Our numerical results are in good agreement with experimental measurements from the optimized antennas fabricated using a two-step electron-beam lithography, revealing the highly directive nature of our structures. We envision that our antenna designs can be conveniently adapted to other dielectric materials and prove instrumental for inter-chip optical communications and other on-chip applications.}}, author = {{Farheen, Henna and Yan, Lok-Yee and Quiring, Viktor and Eigner, Christof and Zentgraf, Thomas and Linden, Stefan and Förstner, Jens and Myroshnychenko, Viktor}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_opticalantenna}}, number = {{11}}, pages = {{19288}}, publisher = {{Optica Publishing Group}}, title = {{{Broadband optical Ta2O5 antennas for directional emission of light}}}, doi = {{10.1364/oe.455815}}, volume = {{30}}, year = {{2022}}, } @article{31574, abstract = {{We model negative polarization, which is observed for planetary regoliths at backscattering, solving a full wave problem of light scattering with a numerically exact Discontinuous Galerkin Time Domain (DGTD) method. Pieces of layers with the bulk packing density of particles close to 0.5 are used. The model particles are highly absorbing and have irregular shapes and sizes larger than the wavelength of light. This represents a realistic analog of low-albedo planetary regoliths. Our simulations confirm coherent backscattering mechanism of the origin of negative polarization. We show that angular profiles of polarization are stabilized if the number of particles in a layer piece becomes larger than ten. This allows application of our approach to the negative polarization modeling for planetary regoliths.}}, author = {{Grynko, Yevgen and Shkuratov, Yuriy and Alhaddad, Samer and Förstner, Jens}}, issn = {{0019-1035}}, journal = {{Icarus}}, keywords = {{tet_topic_scattering}}, pages = {{115099}}, publisher = {{Elsevier BV}}, title = {{{Negative polarization of light at backscattering from a numerical analog of planetary regoliths}}}, doi = {{10.1016/j.icarus.2022.115099}}, volume = {{384}}, year = {{2022}}, } @article{35128, abstract = {{Here we demonstrate a new, to the best of our knowledge, type of 3-dB coupler that has an ultra-broadband operational range from 1300 to 1600 nm with low fabrication sensitivity. The overall device size is 800 µm including in/out S-bend waveguides. The coupler is an asymmetric non-uniform directional coupler that consists of two tapered waveguides. One of the coupler arms is shifted by 100 µm in the propagation direction, which results in a more wavelength-insensitive 3-dB response compared to a standard (not shifted) coupler. Moreover, compared to a long adiabatic coupler, we achieved a similar wavelength response at a 16-times-smaller device length. The couplers were fabricated using the silicon nitride platform of Lionix International. We also experimentally demonstrated an optical switch that is made by using two of these couplers in a Mach–Zehnder interferometer configuration. According to experimental results, this optical switch exhibits –10 dB of extinction ratio over the 1500–1600 nm wavelength range. Our results indicate that this new type of coupler holds great promise for various applications, including optical imaging, telecommunications, and reconfigurable photonic processors where compact, fabrication-tolerant, and wavelength-insensitive couplers are essential.}}, author = {{Nikbakht, Hamed and Khoshmehr, Mohammad Talebi and van Someren, Bob and Teichrib, Dieter and Hammer, Manfred and Förstner, Jens and Akca, B. Imran}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{tet_topic_waveguide}}, number = {{2}}, pages = {{207}}, publisher = {{Optica Publishing Group}}, title = {{{Asymmetric, non-uniform 3-dB directional coupler with 300-nm bandwidth and a small footprint}}}, doi = {{10.1364/ol.476537}}, volume = {{48}}, year = {{2022}}, } @inbook{33466, abstract = {{We review our results of numerical simulations of light scattering from different systems of densely packed irregular particles. We consider spherical clusters, thick layers and monolayers with realistic topologies and dimensions much larger than the wavelength of light. The maximum bulk packing density of clusters is 0.5. A numerically exact solution of the electromagnetic problem is obtained using the Discontinuous Galerkin Time Domain method and with application of high- performance computing. We show that high packing density causes light localization in such structures which makes an impact on the opposition phenomena: backscattering intensity surge and negative linear polarization feature. Diffuse multiple scattering is significantly reduced in the case of non-absorbing particles and near-field interaction results in a percolation-like light transport determined by the topology of the medium. With this the negative polarization feature caused by single scattering gets enhanced if compared to lower density samples. We also confirm coherent double scattering mechanism of negative polarization for light scattered from dense absorbing slabs. In this case convergent result for the scattering angle polarization dependency at backscattering can be obtained for a layer of just a few tens of particles if they are larger than the wavelength.}}, author = {{Grynko, Yevgen and Shkuratov, Yuriy and Alhaddad, Samer and Förstner, Jens}}, booktitle = {{Springer Series in Light Scattering - Volume 8: Light Polarization and Multiple Scattering in Turbid Media}}, editor = {{Kokhanovsky, Alexander}}, isbn = {{9783031102974}}, issn = {{2509-2790}}, keywords = {{tet_topic_scattering}}, publisher = {{Springer International Publishing}}, title = {{{Light Scattering by Large Densely Packed Clusters of Particles}}}, doi = {{10.1007/978-3-031-10298-1_4}}, volume = {{8}}, year = {{2022}}, } @article{30210, abstract = {{Lithium niobate on insulator (LNOI) has a great potential for photonic integrated circuits, providing substantial versatility in design of various integrated components. To properly use these components in the implementation of different quantum protocols, photons with different properties are required. In this paper, we theoretically demonstrate a flexible source of correlated photons built on the LNOI waveguide of a special geometry. This source is based on the parametric down-conversion (PDC) process, in which the signal and idler photons are generated at the telecom wavelength and have different spatial profiles and polarizations, but the same group velocities. Distinguishability in polarizations and spatial profiles facilitates the routing and manipulating individual photons, while the equality of their group velocities leads to the absence of temporal walk-off between photons. We show how the spectral properties of the generated photons and the number of their frequency modes can be controlled depending on the pump characteristics and the waveguide length. Finally, we discuss special regimes, in which narrowband light with strong frequency correlations and polarization-entangled Bell states are generated at the telecom wavelength.}}, author = {{Ebers, Lena and Ferreri, Alessandro and Hammer, Manfred and Albert, Maximilian and Meier, Cedrik and Förstner, Jens and Sharapova, Polina R.}}, issn = {{2515-7647}}, journal = {{Journal of Physics: Photonics}}, keywords = {{tet_topic_waveguide}}, pages = {{025001}}, publisher = {{IOP Publishing}}, title = {{{Flexible source of correlated photons based on LNOI rib waveguides}}}, doi = {{10.1088/2515-7647/ac5a5b}}, volume = {{4}}, year = {{2022}}, } @inproceedings{30389, abstract = {{Online solvers for a series of standard 1-D or 2-D problems in integrated optics will be discussed. Implemented on the basis of HTML/JavaScript/SVG with core routines compiled from well tested C++-sources, the quasi-analytical algorithms require a computational load that can be handled easily even by current mobile devices. So far the series covers the 1-D guided modes of dielectric multilayer slab waveguides and the oblique plane wave reflection from these, the modes of rectangular channel waveguides (in an approximation of effective indices), bend modes of curved multilayer slabs, whispering-gallery resonances (“Quasi-Normal-Modes”) supported by circular dielectric cavities, the hybrid modes of circular multi-step-index optical fibers, bound and leaky modes of 1-D complex multilayers, including plasmonic surface modes, and, with restrictions, quite general rectangular scattering problems in 2-D.}}, author = {{Hammer, Manfred}}, booktitle = {{Integrated Optics: Devices, Materials, and Technologies XXVI}}, editor = {{García-Blanco, Sonia M. and Cheben, Pavel}}, keywords = {{tet_topic_waveguide}}, pages = {{1200414}}, publisher = {{SPIE}}, title = {{{Small-scale online simulations in guided-wave photonics}}}, doi = {{10.1117/12.2612208}}, year = {{2022}}, } @inproceedings{33509, abstract = {{In this publication a novel method for far-field prediction from magnetic Huygens box data based on the boundary element method (BEM) is presented. Two examples are considered for the validation of this method. The first example represents an electric dipole so that the obtained calculations can be compared to an analytical solution. As a second example, a printed circuit board is considered and the calculated far-field is compared to a fullwave simulation. In both cases, the calculations for different field integral equations are under comparison, and the results indicate that the presented method performs very well with a combined field integral equation, for the specified problem, when only magnetic Huygens box data is given.}}, author = {{Marschalt, Christoph and Schroder, Dominik and Lange, Sven and Hilleringmann, Ulrich and Hedayat, Christian and Kuhn, Harald and Sievers, Denis and Förstner, Jens}}, booktitle = {{2022 Smart Systems Integration (SSI)}}, keywords = {{Near-Field Scanning, Huygens Box, Boundary Element Method, Method of Moments, tet_topic_hf}}, location = {{Grenoble, France}}, publisher = {{IEEE}}, title = {{{Far-field Calculation from magnetic Huygens Box Data using the Boundary Element Method}}}, doi = {{10.1109/ssi56489.2022.9901431}}, year = {{2022}}, } @article{21821, abstract = {{We present a combined experimental and numerical study of the far-field emission properties of optical travelling wave antennas made from low-loss dielectric materials. The antennas considered here are composed of two simple building blocks, a director and a reflector, deposited on a glass substrate. Colloidal quantum dots placed in the feed gap between the two elements serve as internal light source. The emission profile of the antenna is mainly formed by the director while the reflector suppresses backward emission. Systematic studies of the director dimensions as well as variation of antenna material show that the effective refractive index of the director primarily governs the far-field emission pattern. Below cut off, i.e., if the director’s effective refractive index is smaller than the refractive index of the substrate, the main lobe results from leaky wave emission along the director. In contrast, if the director supports a guided mode, the emission predominately originates from the end facet of the director.}}, author = {{Leuteritz, T. and Farheen, H. and Qiao, S. and Spreyer, F. and Schlickriede, Christian and Zentgraf, Thomas and Myroshnychenko, Viktor and Förstner, Jens and Linden, S.}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_opticalantenna}}, number = {{10}}, title = {{{Dielectric travelling wave antennas for directional light emission}}}, doi = {{10.1364/oe.422984}}, volume = {{29}}, year = {{2021}}, } @article{21932, abstract = {{Gaussian-beam-like bundles of semi-guided waves propagating in a dielectric slab can excite modes with high-order optical angular momentum supported by a circular fiber. We consider a multimode step-index fiber with a high-index coating, where the waves in the slab are evanescently coupled to the modes of the fiber. Conditions for effective resonant interaction are identified. Based on a hybrid analytical–numerical coupled mode model, our simulations predict that substantial fractions of the input power can be focused into waves with specific orbital angular momentum, of excellent purity, with a clear distinction between degenerate modes with opposite vorticity.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguides}}, number = {{5}}, pages = {{1717}}, title = {{{Resonant evanescent excitation of guided waves with high-order optical angular momentum}}}, doi = {{10.1364/josab.422731}}, volume = {{38}}, year = {{2021}}, } @article{28196, abstract = {{We show that narrow trenches in a high-contrast silicon-photonics slab can act as lossless power dividers for semi-guided waves. Reflectance and transmittance can be easily configured by selecting the trench width. At sufficiently high angles of incidence, the devices are lossless, apart from material attenuation and scattering due to surface roughness. We numerically simulate a series of devices within the full 0-to-1-range of splitting ratios, for semi-guided plane wave incidence as well as for excitation by focused Gaussian wave bundles. Straightforward cascading of the trenches leads to concepts for 1×M-power dividers and a polarization beam splitter.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{2578-7519}}, journal = {{OSA Continuum}}, keywords = {{tet_topic_waveguide}}, number = {{12}}, pages = {{3081}}, title = {{{Configurable lossless broadband beam splitters for semi-guided waves in integrated silicon photonics}}}, doi = {{10.1364/osac.437549}}, volume = {{4}}, year = {{2021}}, } @article{23728, abstract = {{We demonstrate the integration of amorphous tungsten silicide superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides. We show proof-of-principle detection of evanescently coupled photons of 1550 nm wavelength using bidirectional waveguide coupling for two orthogonal polarization directions. We investigate the internal detection efficiency as well as detector absorption using coupling-independent characterization measurements. Furthermore, we describe strategies to improve the yield and efficiency of these devices.}}, author = {{Höpker, Jan Philipp and Verma, Varun B and Protte, Maximilian and Ricken, Raimund and Quiring, Viktor and Eigner, Christof and Ebers, Lena and Hammer, Manfred and Förstner, Jens and Silberhorn, Christine and Mirin, Richard P and Woo Nam, Sae and Bartley, Tim}}, issn = {{2515-7647}}, journal = {{Journal of Physics: Photonics}}, pages = {{034022}}, title = {{{Integrated superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides}}}, doi = {{10.1088/2515-7647/ac105b}}, volume = {{3}}, year = {{2021}}, } @article{27099, abstract = {{In our work, we have engineered low capacitance single quantum dot photodiodes as sensor devices for the optoelectronic sampling of ultrafast electric signals. By the Stark effect, a time-dependent electric signal is converted into a time-dependent shift of the transition energy. This shift is measured accurately by resonant ps laser spectroscopy with photocurrent detection. In our experiments, we sample the laser synchronous output pulse of an ultrafast CMOS circuit with high resolution. With our quantum dot sensor device, we were able to sample transients below 20 ps with a voltage resolution in the mV-range.}}, author = {{Widhalm, Alex and Krehs, Sebastian and Siebert, Dustin and Sharma, Nand Lal and Langer, Timo and Jonas, Björn and Reuter, Dirk and Thiede, Andreas and Förstner, Jens and Zrenner, Artur}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, keywords = {{tet_topic_qd}}, pages = {{181109}}, title = {{{Optoelectronic sampling of ultrafast electric transients with single quantum dots}}}, doi = {{10.1063/5.0061358}}, volume = {{119}}, year = {{2021}}, } @article{23816, abstract = {{Employing the ultrafast control of electronic states of a semiconductor quantum dot in a cavity, we introduce an approach to achieve on-demand emission of single photons with almost perfect indistinguishability and photon pairs with near ideal entanglement. Our scheme is based on optical excitation off resonant to a cavity mode followed by ultrafast control of the electronic states using the time-dependent quantum-confined Stark effect, which then allows for cavity-resonant emission. Our theoretical analysis considers cavity-loss mechanisms, the Stark effect, and phonon-induced dephasing, allowing realistic predictions for finite temperatures.}}, author = {{Bauch, David and Heinze, Dirk Florian and Förstner, Jens and Jöns, Klaus and Schumacher, Stefan}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, pages = {{085308}}, title = {{{Ultrafast electric control of cavity mediated single-photon and photon-pair generation with semiconductor quantum dots}}}, doi = {{10.1103/physrevb.104.085308}}, volume = {{104}}, year = {{2021}}, } @inbook{21587, abstract = {{Solving partial differential equations on unstructured grids is a cornerstone of engineering and scientific computing. Nowadays, heterogeneous parallel platforms with CPUs, GPUs, and FPGAs enable energy-efficient and computationally demanding simulations. We developed the HighPerMeshes C++-embedded Domain-Specific Language (DSL) for bridging the abstraction gap between the mathematical and algorithmic formulation of mesh-based algorithms for PDE problems on the one hand and an increasing number of heterogeneous platforms with their different parallel programming and runtime models on the other hand. Thus, the HighPerMeshes DSL aims at higher productivity in the code development process for multiple target platforms. We introduce the concepts as well as the basic structure of the HighPerMeshes DSL, and demonstrate its usage with three examples, a Poisson and monodomain problem, respectively, solved by the continuous finite element method, and the discontinuous Galerkin method for Maxwell’s equation. The mapping of the abstract algorithmic description onto parallel hardware, including distributed memory compute clusters, is presented. Finally, the achievable performance and scalability are demonstrated for a typical example problem on a multi-core CPU cluster.}}, author = {{Alhaddad, Samer and Förstner, Jens and Groth, Stefan and Grünewald, Daniel and Grynko, Yevgen and Hannig, Frank and Kenter, Tobias and Pfreundt, Franz-Josef and Plessl, Christian and Schotte, Merlind and Steinke, Thomas and Teich, Jürgen and Weiser, Martin and Wende, Florian}}, booktitle = {{Euro-Par 2020: Parallel Processing Workshops}}, isbn = {{9783030715922}}, issn = {{0302-9743}}, keywords = {{tet_topic_hpc}}, title = {{{HighPerMeshes – A Domain-Specific Language for Numerical Algorithms on Unstructured Grids}}}, doi = {{10.1007/978-3-030-71593-9_15}}, year = {{2021}}, } @article{24788, author = {{Alhaddad, Samer and Förstner, Jens and Groth, Stefan and Grünewald, Daniel and Grynko, Yevgen and Hannig, Frank and Kenter, Tobias and Pfreundt, Franz‐Josef and Plessl, Christian and Schotte, Merlind and Steinke, Thomas and Teich, Jürgen and Weiser, Martin and Wende, Florian}}, issn = {{1532-0626}}, journal = {{Concurrency and Computation: Practice and Experience}}, keywords = {{tet_topic_hpc}}, pages = {{e6616}}, title = {{{The HighPerMeshes framework for numerical algorithms on unstructured grids}}}, doi = {{10.1002/cpe.6616}}, year = {{2021}}, } @article{20189, abstract = {{A dielectric step-index optical fiber with tube-like profile is considered, being positioned with a small gap on top of a dielectric slab waveguide. We propose a 2.5-D hybrid analytical/numerical coupled mode model for the evanescent excitation of the tube through semi-guided waves propagating in the slab at oblique angles. The model combines the directional polarized modes supported by the slab with analytic solutions for the TE-, TM-, and orbital-angular-momentum (OAM) modes of the tube-shaped fiber. Implementational details of the scheme are discussed, complemented by finite-element simulations for verification purposes. Our results include configurations with resonant in-fiber excitation of OAM modes with large orbital angular momentum and strong field enhancement.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{0306-8919}}, journal = {{Optical and Quantum Electronics}}, keywords = {{tet_topic_waveguides}}, title = {{{Hybrid coupled mode modelling of the evanescent excitation of a dielectric tube by semi-guided waves at oblique angles}}}, doi = {{10.1007/s11082-020-02595-z}}, volume = {{52}}, year = {{2020}}, } @article{20233, abstract = {{The challenge of designing new tunable nonlinear dielectric materials with tailored properties has attracted an increasing amount of interest recently. Herein, we study the effective nonlinear dielectric response of a stochastic paraelectric-dielectric composite consisting of equilibrium distributions of circular and partially penetrable disks (or parallel, infinitely long, identical, partially penetrable, circular cylinders) of a dielectric phase randomly dispersed in a continuous matrix of a paraelectric phase. The random microstructures were generated using the Metropolis Monte Carlo algorithm. The evaluation of the effective permittivity and tunability were carried out by employing either a Landau thermodynamic model or its Johnson’s approximation to describe the field-dependent permittivity of the paraelectric phase and solving continuum-electrostatics equations using finite element calculations. We reveal that the percolation threshold in this composite governs the critical behavior of the effective permittivity and tunability. For microstructures below the percolation threshold, our simulations demonstrate a strong nonlinear behaviour of the field-dependent effective permittivity and very high tunability that increases as a function of dielectric phase concentration. Above the percolation threshold, the effective permittivity shows the tendency to linearization and the tunability dramatically drops down. The highly reduced permittivity and extraordinarily high tunability are obtained for the composites with dielectric impenetrable disks at high concentrations, in which the triggering of the percolation transition is avoided. The reported results cast light on distinct nonlinear behaviour of 2D and 3D stochastic composites and can guide the design of novel composites with the controlled morphology and tailored permittivity and tunability.}}, author = {{Myroshnychenko, Viktor and Smirnov, Stanislav and Jose, Pious Mathews Mulavarickal and Brosseau, Christian and Förstner, Jens}}, issn = {{1359-6454}}, journal = {{Acta Materialia}}, pages = {{116432}}, title = {{{Nonlinear dielectric properties of random paraelectric-dielectric composites}}}, doi = {{10.1016/j.actamat.2020.10.051}}, volume = {{203}}, year = {{2020}}, } @article{17803, abstract = {{We numerically simulate multiple light scattering in discrete disordered media represented by large clusters of irregular non-absorbing particles. The packing density of clusters is 0.5. With such conditions diffuse scattering is significantly reduced and light transport follows propagation channels that are determined by the particle size and topology of the medium. This kind of localization produces coherent backscattering intensity surge and enhanced negative polarization branch if compared to lower density samples.}}, author = {{Grynko, Yevgen and Shkuratov, Yuriy and Förstner, Jens}}, issn = {{0022-4073}}, journal = {{Journal of Quantitative Spectroscopy and Radiative Transfer}}, keywords = {{tet_topic_scattering}}, pages = {{107234}}, title = {{{Light backscattering from large clusters of densely packed irregular particles}}}, doi = {{10.1016/j.jqsrt.2020.107234}}, volume = {{255}}, year = {{2020}}, } @article{20372, abstract = {{A stepwise angular spectrum method (SASM) for curved interfaces is presented to calculate the wave propagation in planar lens-like integrated optical structures based on photonic slab waveguides. The method is derived and illustrated for an effective 2D setup first and then for 3D slab waveguide lenses. We employ slab waveguides of different thicknesses connected by curved surfaces to realize a lens-like structure. To simulate the wave propagation in 3D including reflection and scattering losses, the stepwise angular spectrum method is combined with full vectorial finite element computations for subproblems with lower complexity. Our SASM results show excellent agreement with rigorous numerical simulations of the full structures with a substantially lower computational effort and can be utilized for the simulation-based design and optimization of complex and large scale setups.}}, author = {{Ebers, Lena and Hammer, Manfred and Förstner, Jens}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_waveguides}}, number = {{24}}, pages = {{36361}}, title = {{{Light diffraction in slab waveguide lenses simulated with the stepwise angular spectrum method}}}, doi = {{10.1364/oe.409612}}, volume = {{28}}, year = {{2020}}, } @inproceedings{21719, abstract = {{We fabricate silicon tapers to increase the mode overlap of superconducting detectors on Ti:LiNbO3 waveguides. Mode images show a reduction in mode size from 6 µm to 2 µm FWHM, agreeing with beam propagation simulations.}}, author = {{Protte, Maximilian and Ebers, Lena and Hammer, Manfred and Höpker, Jan Philipp and Albert, Maximilian and Quiring, Viktor and Meier, Cedrik and Förstner, Jens and Silberhorn, Christine and Bartley, Tim}}, booktitle = {{OSA Quantum 2.0 Conference}}, isbn = {{9781943580811}}, keywords = {{tet_topic_waveguide}}, title = {{{Towards Semiconductor-Superconductor-Crystal Hybrid Integration for Quantum Photonics}}}, doi = {{10.1364/quantum.2020.qth7a.8}}, year = {{2020}}, } @article{17322, author = {{Mukherjee, Amlan and Widhalm, Alex and Siebert, Dustin and Krehs, Sebastian and Sharma, Nandlal and Thiede, Andreas and Reuter, Dirk and Förstner, Jens and Zrenner, Artur}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, keywords = {{tet_topic_qd}}, pages = {{251103}}, title = {{{Electrically controlled rapid adiabatic passage in a single quantum dot}}}, doi = {{10.1063/5.0012257}}, volume = {{116}}, year = {{2020}}, } @inproceedings{39966, author = {{Förstner, Jens and Widhalm, A. and Mukherjee, A. and Krehs, S. and Jonas, B. and Spychala, K. and Förstner, Jens and Thiede, Andreas and Reuter, Dirk and Zrenner, Artur}}, booktitle = {{11th International Conference on Quantum Dots}}, title = {{{Ultrafast electric control of a single QD exciton}}}, year = {{2020}}, } @inproceedings{21462, abstract = {{This paper presents a new methodology by using a multiple coil array for energy transmission. The complex current strengths of the transmitting coil array are calculated by having the knowledge about of the mutual inductances and the symmetries of the transmitting coil array, so that its resulting magnetic field mainly penetrates only the receiving coil and is strongly attenuated outside. This method is used for an optimized wireless energy transmission but can also be implemented for other inductive applications.}}, author = {{Lange, Sven and Büker, Maik-Julian and Sievers, Denis and Hedayat, Christian and Förstner, Jens and Hilleringmann, Ulrich and Otto, Thomas}}, booktitle = {{Smart Systems Integration; 13th International Conference and Exhibition on Integration Issues of Miniaturized Systems}}, isbn = {{978-3-8007-4919-5}}, location = {{Barcelona, Spain }}, pages = {{1--4}}, publisher = {{VDE VERLAG GMBH}}, title = {{{Method of superposing a multiple driven magnetic field to minimize stray fields around the receiver for inductive wireless power transmission}}}, year = {{2019}}, } @article{8872, abstract = {{We consider light scattering from a new type of model particle whose shape is represented in the form of a generalized ellipsoid having N foci, where N is greater than two. Such particles can be convex as well as concave. We use the geometrical optics approximation to study the light scattering from 3-foci particles. Non-zero elements of the scattering matrix are calculated for ensembles of randomly oriented independent transparent particles, m = n + i0. Several internal reflection orders are considered separately. It was found that the transmission-transmission (TT) and transmission-reflectance-transmission (TRT) components dominate in the formation of intensity of scattered light at large and small phase angles, respectively. We found a significant role of the total internal reflections of the TRT in the middle portion of the phase angle range. The main factors in the formation of positive linear polarization are the R and TRT component. The TT component is responsible for the formation of negative polarization branch at large phase angles.}}, author = {{Stankevich, Dmitriy and Hradyska, Larissa and Shkuratov, Yuriy and Grynko, Yevgen and Videen, Gorden and Förstner, Jens}}, issn = {{0022-4073}}, journal = {{Journal of Quantitative Spectroscopy and Radiative Transfer}}, keywords = {{tet_topic_scattering}}, pages = {{49}}, title = {{{Light scattering by 3-Foci convex and concave particles in the geometrical optics approximation}}}, doi = {{10.1016/j.jqsrt.2019.04.016}}, volume = {{231}}, year = {{2019}}, } @article{12908, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguides}}, pages = {{2395}}, title = {{{Oblique quasi-lossless excitation of a thin silicon slab waveguide: a guided-wave variant of an anti-reflection coating}}}, doi = {{10.1364/josab.36.002395}}, volume = {{36}}, year = {{2019}}, } @article{14990, abstract = {{We investigate optical microresonators consisting of either one or two coupled rectangular strips between upper and lower slab waveguides. The cavities are evanescently excited under oblique angles by thin-film guided, in-plane unguided waves supported by one of the slab waveguides. Beyond a specific incidence angle, losses are fully suppressed. The interaction between the guided mode of the cavity-strip and the incoming slab modes leads to resonant behavior for specific incidence angles and gaps. For a single cavity, at resonance, the input power is equally split among each of the four output ports, while for two cavities an add-drop filter can be realized that, at resonance, routes the incoming power completely to the forward drop waveguide via the cavity. For both applications, the strength of the interaction is controlled by the gaps between cavities and waveguides.}}, author = {{Ebers, Lena and Hammer, Manfred and Berkemeier, Manuel B. and Menzel, Alexander and Förstner, Jens}}, issn = {{2578-7519}}, journal = {{OSA Continuum}}, keywords = {{tet_topic_waveguides}}, pages = {{3288}}, title = {{{Coupled microstrip-cavities under oblique incidence of semi-guided waves: a lossless integrated optical add-drop filter}}}, doi = {{10.1364/osac.2.003288}}, volume = {{2}}, year = {{2019}}, } @misc{7720, abstract = {{Die Erfindung betrifft einen optischen Übergang zwischen zwei optischen Schichtwellenleitern. Dazu ist eine Anordnung vorgesehen aus einem ersten optischen Schichtwellenleiter (2) und einem zweiten optischen Schichtwellenleiter (3), wobei der erste optische Schichtwellenleiter (2) und der zweite optische Schichtwellenleiter (3) voneinander verschiedene über ihre jeweilige Länge konstante Dicken (d, r) aufweisen, der erste optische Schichtwellenleiter (2) mit dem zweiten optischen Schichtwellenleiter (3) mittels einer optischen Schichtwellenleiterstruktur (4) verbunden ist, die über ihre gesamte Länge (w) eine Dicke (h) aufweist, die zwischen der Dicke (d) des ersten optischen Schichtwellenleiters (2) und der Dicke (r) des zweiten optischen Schichtwellenleiters (3) liegt. Erfindungsgemäß ist die Dicke (h) der optischen Schichtwellenleiterstruktur (4) über die gesamte Länge (w) der optischen Schichtwellenleiterstruktur (4) konstant. Damit wird eine Möglichkeit für einen effizienten und mit geringen Verlusten behafteten Übergang zwischen zwei optischen Schichtwellenleitern mit unterschiedlicher Dicke bereitgestellt. }}, author = {{Hammer, Manfred and Förstner, Jens and Ebers, Lena}}, keywords = {{tet_topic_waveguides}}, pages = {{9}}, title = {{{Optical transition between two optical waveguides layer and method for transmitting light}}}, year = {{2019}}, } @article{8634, abstract = {{A rectangular dielectric strip at some distance above an optical slab waveguide is being considered, for evanescent excitation of the strip through the semi-guided waves supported by the slab, at specific oblique angles. The 2.5-D configuration shows resonant transmission properties with respect to variations of the angle of incidence, or of the excitation frequency, respectively. The strength of the interaction can be controlled by the gap between strip and slab. For increasing distance, our simulations predict resonant states with unit extremal reflectance of an angular or spectral width that tends to zero, i.e. resonances with a Q-factor that tends to infinity, while the resonance position approaches the level of the guided mode of the strip. This exceptionally simple system realizes what might be termed a “bound state coupled to the continuum”.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, journal = {{Optics Express}}, keywords = {{tet_topic_waveguides}}, number = {{7}}, pages = {{8}}, title = {{{Oblique evanescent excitation of a dielectric strip: A model resonator with an open optical cavity of unlimited Q}}}, doi = {{10.1364/OE.27.009313}}, volume = {{27}}, year = {{2019}}, } @inproceedings{3588, abstract = {{In scientific computing, unstructured meshes are a crucial foundation for the simulation of real-world physical phenomena. Compared to regular grids, they allow resembling the computational domain with a much higher accuracy, which in turn leads to more efficient computations.
There exists a wealth of supporting libraries and frameworks that aid programmers with the implementation of applications working on such grids, each built on top of existing parallelization technologies. However, many approaches require the programmer to introduce a different programming paradigm into their application or provide different variants of the code. SYCL is a new programming standard providing a remedy to this dilemma by building on standard C ++17 with its so-called single-source approach: Programmers write standard C ++ code and expose parallelism using C++17 keywords. The application is
then transformed into a concrete implementation by the SYCL implementation. By encapsulating the OpenCL ecosystem, different SYCL implementations enable not only the programming of CPUs but also of heterogeneous platforms such as GPUs or other devices. For the first time, this paper showcases a SYCL-
based solver for the nodal Discontinuous Galerkin method for Maxwell’s equations on unstructured meshes. We compare our solution to a previous C-based implementation with respect to programmability and performance on heterogeneous platforms., /Y>), insbesondere die mit zueinander orthogonalen Polarisationen (P1, P2) optisch anregbar sind, mit einem ersten Laserpuls (L1) beleuchtet wird, welcher zur resonanten Anregung des ersten (/Y>) der zwei Zustände (/X>, /Y>) eingestellt wird und zeitlich nachfolgend mit einem zweiten Laserpuls (L2) beleuchtet wird, der zur resonanten Anregung des zweiten (/X>) der zwei Zustände (/X>, /Y>) eingestellt wird.}}, author = {{Zrenner, Artur and Förstner, Jens and Mantei, Dirk}}, keywords = {{tet_topic_qd}}, title = {{{A process for the preparation of a population inversion in a quantum system using multi-pulse excitation}}}, year = {{2015}}, } @article{3890, abstract = {{The incidenceofthin-film-guided, in-planeunguidedwavesatobliqueanglesonstraightdiscontinuities of dielectricslabwaveguides,anearlyproblemofintegratedoptics,isbeingre-considered.The3-D frequencydomainMaxwellequationsreducetoaparametrizedinhomogeneousvectorialproblemona 2-D computationaldomain,withtransparent-influx boundaryconditions.Weproposearigorousvec- torial solverbasedonsimultaneousexpansionsintopolarizedlocalslabeigenmodesalongthetwo orthogonal crosssectioncoordinates(quadridirectionaleigenmodepropagationQUEP).Thequasi-ana- lytical schemeisapplicabletoconfigurations with — in principle — arbitrary crosssectiongeometries. Examples forahigh-contrastfacetofanasymmetricslabwaveguide,forthelateralexcitationofa channel waveguide,andforastepdiscontinuitybetweenslabwaveguidesofdifferentthicknessesare discussed.}}, author = {{Hammer, Manfred}}, issn = {{0030-4018}}, journal = {{Optics Communications}}, keywords = {{tet_topic_waveguide, tet_topic_numerics}}, pages = {{447--456}}, publisher = {{Elsevier BV}}, title = {{{Oblique incidence of semi-guided waves on rectangular slab waveguide discontinuities: A vectorial QUEP solver}}}, doi = {{10.1016/j.optcom.2014.09.087}}, volume = {{338}}, year = {{2014}}, } @article{3937, abstract = {{The relevance of our definition for sensitivity in refractometric sensing, being the relative change in the transmittance of a certain output channel of an optical device over the change in the refractive index of the probed material, is discussed. It is compared to one based on spectral shift per refractive index unit change. Further, there is discussion on how group delay and sensitivity are interrelated and can be converted into each other and which physical quantities are relevant for high sensitivity. As a by-product of the theory presented, a general expression relating group delay and the ratio of the time-averaged optical energy and the input power is presented.}}, author = {{Hoekstra, Hugo J. W. M. and Hammer, Manfred}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguide}}, number = {{7}}, publisher = {{The Optical Society}}, title = {{{General relation for group delay and the relevance of group delay for refractometric sensing}}}, doi = {{10.1364/josab.31.001561}}, volume = {{31}}, year = {{2014}}, } @inbook{3941, author = {{Declair, Stefan and Förstner, Jens}}, booktitle = {{Handbook of Optical Microcavities}}, editor = {{Choi, Anthony H.W.}}, keywords = {{tet_topic_phc}}, publisher = {{Pan Stanford Publishing Pte. Ltd.}}, title = {{{Simulation of Planar Photonic Resonators}}}, volume = {{Kapitel 2}}, year = {{2014}}, } @inproceedings{4315, abstract = {{We simulate numerically light scattering by random irregular particles of two classes of shape: Gaussian random field particles and agglomerated debri particles. Comparison of the angular dependencies of the scattering matrix elements for the case of non-absorbing material shows qualitative similarity of optical properties of both types despite different morphology of scatterers. Absorbing particles result in the difference in linear polarization. However, a strong similarty remains for the intensity curves.}}, author = {{Grynko, Yevgen and Zubko, Evgenij}}, location = {{Marseille (France)}}, title = {{{Light Scattering By Random Irregular Particles With Different Morphology}}}, year = {{2014}}, } @inproceedings{3939, abstract = {{Optical and infrared antennas provide a promising way to couple photons in and out of nanoscale structures. As counterpart to conventional radio antennas, they are able to increase optical felds in sub-wavelength volumes, to enhance excitation and emission of quantum emitters or to direct light, radiated by quantum emitters. The directed emission of these antennas has been mainly pursued by surface plasmon based devices, e.g. Yagi-Uda like antennas, which are rather complicated due to the coupling of several metallic particles. Also, like all metallic structures in optical or infrared regime, these devices are very sensitive to fabrication tolerances and are affected by strong losses. It has been shown recently, that such directed emission can be accomplished by dielectric materials as well. In this paper we present an optimization of nanoscopic antennas in the near infrared regime starting from a metallic Yagi-Uda structure. The optimization is done via a particle-swarm algorithm, using full time domain finite integration simulations to obtain the characteristics of the investigated structure, also taking into account substrates. Furthermore we present a dielectric antenna, which performs even better, due to the lack of losses by an appropriate choice of the dielectric material. These antennas are robust concerning fabrication tolerances and can be realized with different materials for both the antenna and the substrate, without using high index materials.}}, author = {{Hildebrandt, Andre and Reichelt, Matthias and Meier, Torsten and Förstner, Jens}}, booktitle = {{Ultrafast Phenomena and Nanophotonics XVIII}}, editor = {{Betz, Markus and Elezzabi, Abdulhakem Y. and Song, Jin-Joo and Tsen, Kong-Thon}}, keywords = {{tet_topic_opticalantenna}}, pages = {{89841G--8941G--6}}, publisher = {{SPIE}}, title = {{{Engineering plasmonic and dielectric directional nanoantennas}}}, doi = {{10.1117/12.2036588}}, volume = {{8984}}, year = {{2014}}, } @article{1779, author = {{Giefers, Heiner and Plessl, Christian and Förstner, Jens}}, issn = {{0163-5964}}, journal = {{ACM SIGARCH Computer Architecture News}}, keywords = {{funding-maxup, tet_topic_hpc}}, number = {{5}}, pages = {{65--70}}, publisher = {{ACM}}, title = {{{Accelerating Finite Difference Time Domain Simulations with Reconfigurable Dataflow Computers}}}, doi = {{10.1145/2641361.2641372}}, volume = {{41}}, year = {{2014}}, } @article{1783, author = {{Grynko, Yevgen and Shkuratov, Yuriy and Förstner, Jens}}, journal = {{Optical Letters}}, keywords = {{tet_topic_scattering}}, number = {{23}}, pages = {{5153--5156}}, title = {{{Light scattering by randomly irregular dielectric particles larger than the wavelength}}}, doi = {{10.1364/OL.38.005153}}, volume = {{38}}, year = {{2013}}, } @article{3959, abstract = {{Microresonators containing quantum dots find application in devices like single photon emitters for quantum information technology as well as low threshold laser devices. We demonstrate the fabrication of 60 nm thin zinc-blende AlN microdisks including cubic GaN quantum dots using dry chemical etching techniques. Scanning electron microscopy analysis reveals the morphology with smooth surfaces of the microdisks. Micro-photoluminescence measurements exhibit optically active quantum dots. Furthermore this is the first report of resonator modes in the emission spectrum of a cubic AlN microdisk.}}, author = {{Bürger, M. and Kemper, R.M. and Bader, C.A. and Ruth, M. and Declair, S. and Meier, Cedrik and Förstner, Jens and As, D.J.}}, issn = {{0022-0248}}, journal = {{Journal of Crystal Growth}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, pages = {{287--290}}, publisher = {{Elsevier BV}}, title = {{{Cubic GaN quantum dots embedded in zinc-blende AlN microdisks}}}, doi = {{10.1016/j.jcrysgro.2012.12.058}}, volume = {{378}}, year = {{2013}}, } @article{3963, abstract = {{Whispering gallery modes (WGMs) were observed in 60 nm thin cubic AlN microdisk resonators containing a single layer of non-polar cubic GaN quantum dots. Freestanding microdisks were patterned by means of electron beam lithography and a two step reactive ion etching process. Micro-photoluminescence spectroscopy investigations were performed for optical characterization. We analyzed the mode spacing for disk diameters ranging from 2-4 lm. Numerical investigations using three dimensional finite difference time domain calculations were in good agreement with the experimental data. Whispering gallery modes of the radial orders 1 and 2 were identified by means of simulated mode field distributions.}}, author = {{Bürger, M. and Ruth, M. and Declair, S. and Förstner, Jens and Meier, Cedrik and As, Donat Josef}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{8}}, pages = {{081105}}, publisher = {{AIP Publishing}}, title = {{{Whispering gallery modes in zinc-blende AlN microdisks containing non-polar GaN quantum dots}}}, doi = {{10.1063/1.4793653}}, volume = {{102}}, year = {{2013}}, } @inproceedings{4039, abstract = {{We perform experiments on resonant second-harmonic generation from planar gold split-ring-resonator arrays under normal incidence of light as a function of the lattice constant. Optimum nonlinear conversion occurs at intermediate lattice constants.}}, author = {{Niesler, Fabian B. and Linden, Stefan and Förstner, Jens and Grynko, Yevgen and Meier, Torsten and Wegener, Martin}}, booktitle = {{Conference on Lasers and Electro-Optics 2012}}, isbn = {{9781557529435}}, keywords = {{tet_topic_shg, tet_topic_meta}}, location = {{San Jose, California United States}}, number = {{1}}, publisher = {{OSA}}, title = {{{Collective effects in second-harmonic generation from split-ring-resonator arrays}}}, doi = {{10.1364/qels.2012.qth3e.2}}, volume = {{109}}, year = {{2013}}, } @inproceedings{3961, abstract = {{Previous experimental measurements and numerical simulations give evidence of strong electric and magnetic field interaction between split-ring resonators in dense arrays. One can expect that such interactions have an influence on the second harmonic generation. We apply the Discontinuous Galerkin Time Domain method and the hydrodynamic Maxwell-Vlasov model to simulate the linear and nonlinear optical response from SRR arrays. The simulations show that dense placement of the constituent building blocks appears not always optimal and collective effects can lead to a significant suppression of the near fields at the fundamental frequency and, consequently, to the decrease of the SHG intensity. We demonstrate also the great role of the symmetry degree of the array layout which results in the variation of the SHG efficiency in range of two orders of magnitude.}}, author = {{Grynko, Yevgen and Meier, Torsten and Linden, Stefan and Niesler, Fabian B. P. and Wegener, Martin and Förstner, Jens}}, booktitle = {{Ultrafast Phenomena and Nanophotonics XVII}}, editor = {{Betz, Markus and Elezzabi, Abdulhakem Y. and Song, Jin-Joo and Tsen, Kong-Thon}}, keywords = {{tet_topic_shg, tet_topic_meta}}, pages = {{86230L--86230L--9}}, publisher = {{SPIE}}, title = {{{Optimal second-harmonic generation in split-ring resonator arrays}}}, doi = {{10.1117/12.2003279}}, volume = {{8623}}, year = {{2013}}, } @article{3974, abstract = {{We study the quantum properties and statistics of photons emitted by a quantum-dot biexciton inside a cavity. In the biexciton-exciton cascade, fine-structure splitting between exciton levels degrades polarization-entanglement for the emitted pair of photons. However, here we show that the polarization-entanglement can be preserved in such a system through simultaneous emission of two degenerate photons into cavity modes tuned to half the biexciton energy. Based on detailed theoretical calculations for realistic quantum-dot and cavity parameters, we quantify the degree of achievable entanglement.}}, author = {{Schumacher, Stefan and Förstner, Jens and Zrenner, Artur and Florian, Matthias and Gies, Christopher and Gartner, Paul and Jahnke, Frank}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_qd}}, number = {{5}}, pages = {{5335--5342}}, publisher = {{OSA}}, title = {{{Cavity-assisted emission of polarization-entangled photons from biexcitons in quantum dots with fine-structure splitting}}}, doi = {{10.1364/oe.20.005335}}, volume = {{20}}, year = {{2012}}, } @inproceedings{3965, abstract = {{We design the geometrical shape of plasmonic nanostructures to achieve field patterns with desired properties. For this, we combine Maxwell simulations and automatic optimization techniques. By allowing variations of the geometrical shape, which can be based on either boxes or arbitrary polygons, we maximize the desired objective.}}, author = {{Hildebrandt, Andre and Reichelt, Matthias and Meier, Torsten and Förstner, Jens}}, keywords = {{tet_topic_optical antenna, tet_topic_plasmonics}}, location = {{Bad Honnef}}, number = {{59}}, publisher = {{AIP AIP Conference Proceedings 1475}}, title = {{{Optimization of the intensity enhancement in plasmonic nanoantennas}}}, doi = {{10.1063/1.4750095}}, year = {{2012}}, } @article{3970, abstract = {{Optical experiments on second-harmonic generation from split-ring-resonator square arrays show a nonmonotonic dependence of the conversion efficiency on the lattice constant. This finding is interpreted in terms of a competition between dilution effects and linewidth or near-field changes due to interactions among the individual elements in the array.}}, author = {{Linden, S. and Niesler, F. B. P. and Förstner, Jens and Grynko, Yevgen and Meier, Torsten and Wegener, M.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_shg, tet_topic_meta}}, number = {{1}}, publisher = {{American Physical Society (APS)}}, title = {{{Collective Effects in Second-Harmonic Generation from Split-Ring-Resonator Arrays}}}, doi = {{10.1103/physrevlett.109.015502}}, volume = {{109}}, year = {{2012}}, } @article{3972, abstract = {{Using a finite-difference time-domain method, we theoretically investigate the optical spectra of crossing perpendicular photonic crystal waveguides with quantum dots embedded in the central rod. The waveguides are designed so that the light mainly propagates along one direction and the cross talk is greatly reduced in the transverse direction. It is shown that when a quantum dot (QD) is resonant with the cavity, strong coupling can be observed via both the transmission and crosstalk spectrum. If the cavity is far off-resonant from the QD, both the cavity mode and the QD signal can be detected in the transverse direction since the laser field is greatly suppressed in this direction. This structure could have strong implications for resonant excitation and in-plane detection of QD optical spectroscopy.}}, author = {{Song, Xiaohong and Declair, Stefan and Meier, Torsten and Zrenner, Artur and Förstner, Jens}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_phc, tet_topic_qd}}, number = {{13}}, pages = {{14130--14136}}, publisher = {{The Optical Society}}, title = {{{Photonic crystal waveguides intersection for resonant quantum dot optical spectroscopy detection}}}, doi = {{10.1364/oe.20.014130}}, volume = {{20}}, year = {{2012}}, } @inproceedings{3967, abstract = {{We simulate the linear and nonlinear optical response from split-ring resonator (SRR) arrays to study collective effects between the constituent SRRs that determine spectral properties of the second harmonic generation (SHG). We apply the Discontinuous Galerkin Time Domain (DGTD) method and the hydrodynamic Maxwell-Vlasov model to calculate the SHG emission. Our model is able to qualitatively reproduce and explain the non-monotonic dependence of the spectral SHG transmission measured experimentally for SRR arrays with different lattice constants}}, author = {{Grynko, Yevgen and Meier, Torsten and Linden, Stefan and Niesler, Fabian B. P. and Wegener, Martin and Förstner, Jens}}, keywords = {{tet_topic_meta, tet_topic_shg}}, location = {{Bad Honnef}}, number = {{1}}, pages = {{128--130}}, publisher = {{AIP Conference Proceedings}}, title = {{{Near-field coupling and second-harmonic generation in split-ring resonator arrays}}}, doi = {{10.1063/1.4750118}}, volume = {{1475}}, year = {{2012}}, } @inproceedings{3980, abstract = {{Paper Abstract High harmonic generation is investigated for a two-band model of a semiconductor nanostructure. Similar to an atomic two-level system, the semiconductor emits high harmonic radiation. We show how one can specifically enhance the emission for a given frequency by applying a non-trivially shaped laser pulse. Therefore, the semiconductor Bloch equations including the interband and additionally the intraband dynamics are solved numerically and the spectral shape of the input pulse is computed via an optimization algorithm. It is demonstrated that desired emission frequencies can be favored even though the overall input power is kept constant. We also suggest special metallic nano geometries to achieve enhanced localized optical fields. They are found by geometric optimization.}}, author = {{Reichelt, Matthias and Hildebrandt, Andre and Walther, Andrea and Förstner, Jens and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena and Nanophotonics XVI}}, isbn = {{9780819489036 }}, keywords = {{tet_topic_shg}}, publisher = {{SPIE}}, title = {{{Engineering high harmonic generation in semiconductors via pulse shaping}}}, doi = {{10.1117/12.906338}}, volume = {{8260}}, year = {{2012}}, } @inproceedings{2106, abstract = {{Although the benefits of FPGAs for accelerating scientific codes are widely acknowledged, the use of FPGA accelerators in scientific computing is not widespread because reaping these benefits requires knowledge of hardware design methods and tools that is typically not available with domain scientists. A promising but hardly investigated approach is to develop tool flows that keep the common languages for scientific code (C,C++, and Fortran) and allow the developer to augment the source code with OpenMPlike directives for instructing the compiler which parts of the application shall be offloaded the FPGA accelerator. In this work we study whether the promise of effective FPGA acceleration with an OpenMP-like programming effort can actually be held. Our target system is the Convey HC-1 reconfigurable computer for which an OpenMP-like programming environment exists. As case study we use an application from computational nanophotonics. Our results show that a developer without previous FPGA experience could create an FPGA-accelerated application that is competitive to an optimized OpenMP-parallelized CPU version running on a two socket quad-core server. Finally, we discuss our experiences with this tool flow and the Convey HC-1 from a productivity and economic point of view.}}, author = {{Meyer, Björn and Schumacher, Jörn and Plessl, Christian and Förstner, Jens}}, booktitle = {{Proc. Int. Conf. on Field Programmable Logic and Applications (FPL)}}, keywords = {{funding-upb-forschungspreis, funding-maxup, tet_topic_hpc}}, pages = {{189--196}}, publisher = {{IEEE}}, title = {{{Convey Vector Personalities – FPGA Acceleration with an OpenMP-like Effort?}}}, doi = {{10.1109/FPL.2012.6339370}}, year = {{2012}}, } @article{4089, abstract = {{We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantumkinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual processes with relevant acoustic phonons. We show that the relaxation is dominated by phononassisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between the quantum dots is studied in detail.}}, author = {{Grodecka-Grad, Anna and Förstner, Jens}}, issn = {{1862-6351}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qd}}, number = {{4}}, pages = {{1125--1128}}, publisher = {{Wiley}}, title = {{{Phonon-assisted decoherence and tunneling in quantum dot molecules}}}, doi = {{10.1002/pssc.201000824}}, volume = {{8}}, year = {{2011}}, } @misc{4171, abstract = {{The method involves exciting a quantum system with photons in a polarization state. Two states of the quantum system are excited with linear horizontal and vertical polarizations that are orthogonal to each other, where the states exhibit an energetic gap smaller than energetic bandwidth of photons. The states are assigned based on the polarizations, where the quantum system is arranged in a superposition state. The quantum system is formed by a quantum bit that is formed as a two-level system.}}, author = {{Förstner, Jens and Mantei, D. and de Vasconcellos, S. Michaelis and Zrenner, Artur}}, keywords = {{tet_topic_qd}}, title = {{{Method for transmission of information about polarization state of photons to stationary system}}}, year = {{2011}}, } @article{4040, abstract = {{We numerically investigate the interaction dynamics of coupled cavities in planar photonic crystal slabs in different configurations. The single cavity is optimized for a long lifetime of the fundamental mode, reaching a Q-factor of ≈43, 000 using the method of gentle confinement. For pairs of cavities we consider several configurations and present a setup with strongest coupling observable as a line splitting of about 30 nm. Based on this configuration, setups with three cavities are investigated.}}, author = {{Declair, S. and Meier, Torsten and Zrenner, Artur and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_phc}}, number = {{4}}, pages = {{345--350}}, publisher = {{Elsevier BV}}, title = {{{Numerical analysis of coupled photonic crystal cavities}}}, doi = {{10.1016/j.photonics.2011.04.012}}, volume = {{9}}, year = {{2011}}, } @article{4044, abstract = {{A simulation environment for metallic nanostructures based on the Discontinuous Galerkin Time Domain method is presented. The model is used to compute the linear and nonlinear optical response of split ring resonators and to study physical mechanisms that contribute to second harmonic generation.}}, author = {{Grynko, Yevgen and Förstner, Jens and Meier, Torsten}}, issn = {{1825-1242}}, journal = {{AAPP | Atti della Accademia Peloritana dei Pericolanti}}, keywords = {{tet_topic_numerics, tet_topic_shg, tet_topic_meta}}, number = {{1}}, title = {{{Application of the discontinous Galerkin time domain method to the optics of metallic nanostructures}}}, doi = {{10.1478/C1V89S1P041}}, volume = {{89}}, year = {{2011}}, } @article{4120, abstract = {{The intensity dependence of optically-induced injection currents in unbiased GaAs semiconductor quantum wells grown in [110] direction is investigated theoretically for a number of well widths. Our microscopic analysis is based on a 14 x 14 band k . p method in combination with the multisubband semiconductor Bloch equations. An oscillatory dependence of the injection current transients as function of intensity and time is predicted and explained. It is demonstrated that optical excitations involving different subbands and Rabi flopping are responsible for this complex dynamics.}}, author = {{Pochwała, Michał and Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, issn = {{1862-6254}}, journal = {{physica status solidi (RRL) - Rapid Research Letters}}, keywords = {{tet_topic_qw}}, number = {{3}}, pages = {{119--121}}, publisher = {{Wiley}}, title = {{{Intensity-dependent ultrafast dynamics of injection currents in unbiased GaAs quantum wells}}}, doi = {{10.1002/pssr.201004529}}, volume = {{5}}, year = {{2011}}, } @article{4049, abstract = {{The injection of photocurrents by femtosecond laser pulses in (110)-orientedGaAs/AlGaAs quantum wells is investigated theoretically and experimentally. The roomtemperature measurements show an oscillatory dependence of the injection current amplitude and direction on the excitation photon energy. Microscopic calculations using the semiconductor Bloch equations that are set up on the basis of k.p band structure calculations provide a detailed understanding of the experimental findings.}}, author = {{Thanh Duc, Huynh and Förstner, Jens and Meier, Torsten and Priyadarshi, Shekhar and Racu, Ana Maria and Pierz, Klaus and Siegner, Uwe and Bieler, Mark}}, issn = {{1862-6351}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qw}}, number = {{4}}, pages = {{1137--1140}}, publisher = {{Wiley}}, title = {{{Oscillatory excitation energy dependence of injection currents in GaAs/AlGaAs quantum wells}}}, doi = {{10.1002/pssc.201000831}}, volume = {{8}}, year = {{2011}}, } @article{4118, abstract = {{We numerically investigate the coupling between circular resonators and study strong light‐matter coupling of single as well as multiple circular resonators to quantum‐mechanical resonators in two dimensional model simulations. For all cases, the computed resonances of the coupled system as function of the detuning show anti‐crossings. The obtained mode splittings of coupled optical resonators are strongly depending on distance and cluster in almost degenerate eigenstates for large distances, as is known from coupled resonator optical waveguides. Vacuum Rabi splitting is observed for a quantum dot strongly coupled to eigenmodes of single perfectly cylindrical resonators. }}, author = {{Declair, S. and Meier, Torsten and Förstner, Jens}}, issn = {{1862-6351}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_phc, tet_topic_microdisk}}, number = {{4}}, pages = {{1254--1257}}, publisher = {{Wiley}}, title = {{{Numerical investigation of the coupling between microdisk modes and quantum dots}}}, doi = {{10.1002/pssc.201000869}}, volume = {{8}}, year = {{2011}}, } @article{4091, abstract = {{We present a nonequilibrium ab initio method for calculating nonlinear and nonlocal optical effects in metallic slabs with a thickness of several nanometers. The numerical analysis is based on the full solution of the time‐dependent Kohn–Sham equations for a jellium system and allows to study the optical response of metal electrons subject to arbitrarily shaped intense light pulses. We find a strong localization of the generated second‐harmonic current in the surface regions of the slabs. }}, author = {{Wand, Mathias and Schindlmayr, Arno and Meier, Torsten and Förstner, Jens}}, issn = {{1521-3951}}, journal = {{Physica Status Solidi B}}, keywords = {{tet_topic_shg}}, number = {{4}}, pages = {{887--891}}, publisher = {{Wiley-VCH}}, title = {{{Simulation of the ultrafast nonlinear optical response of metal slabs}}}, doi = {{10.1002/pssb.201001219}}, volume = {{248}}, year = {{2011}}, } @inproceedings{4312, abstract = {{The intensity dependence of optically-induced injection currents in semiconductor quantum wells is investigated numerically. Oscillatory behavior of the electron charge current transients as function of intensity and time is predicted and explained.}}, author = {{Pochwala, Michal and Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, booktitle = {{CLEO:2011 - Laser Applications to Photonic Applications}}, isbn = {{9781557529107}}, issn = {{2160-8989 }}, keywords = {{tet_topic_qw}}, location = {{Baltimore, Maryland (USA)}}, publisher = {{Optical Society of America}}, title = {{{Intensity dependence of optically-induced injection currents in semiconductor quantum wells}}}, doi = {{10.1364/qels.2011.qmk4}}, year = {{2011}}, } @inproceedings{4043, abstract = {{We present numerical results of the mutual coupling between photonic crystal cavities and semiconductor quantum dots. Normal mode splitting between a single cavity mode and a single quantum dot is shown under weak excitation, while under strong excitation Q‐factor dependent side bands appear, according to the AC‐Stark effect. Coupled photonic crystals, aligned parallel but displaced under a 30°‐angle for efficient coupling, show line splittings of all eigenmodes, if a single eigenmode is resonantly coupled to a single quantum dot. The mutual coupling of N resonant quantum dots to a single cavity mode results in a N−−√ scaling of the splitting, known from quantum optics, but corrected by the field amplitude fraction for not collocated quantum dots.}}, author = {{Declair, S. and Song, X. and Meier, Torsten and Förstner, Jens}}, booktitle = {{THE FOURTH INTERNATIONAL WORKSHOP 2011}}, keywords = {{tet_topic_phc, tet_topic_qd}}, location = {{Bad Honnef}}, number = {{123}}, pages = {{123--125}}, publisher = {{AIP}}, title = {{{Simulation of Mutual Coupling of Photonic Crystal Cavity Modes and Semiconductor Quantum Dots}}}, doi = {{10.1063/1.3644232}}, volume = {{1398}}, year = {{2011}}, } @inproceedings{4048, abstract = {{We present an ab-initio method for calculating nonlinear and nonlocal optical effects in metallic slabs with sub-wavelength thickness. We find a strong localization of the second-harmonic current at the metal-vacuum interface.}}, author = {{Wand, Mathias and Schindlmayr, Arno and Meier, Torsten and Förstner, Jens}}, booktitle = {{CLEO:2011 - Laser Applications to Photonic Applications }}, isbn = {{978-1-4577-1223-4}}, issn = {{2160-8989}}, keywords = {{tet_topic_shg}}, location = {{Baltimore, Maryland, United States}}, publisher = {{Optical Society of America}}, title = {{{Theoretical approach to the ultrafast nonlinear optical response of metal slabs}}}, doi = {{10.1364/CLEO_AT.2011.JTuI59}}, year = {{2011}}, } @inproceedings{4122, abstract = {{We experimentally and theoretically investigate injection currents generated by femtosecond single-color circularly-polarized laser pulses in (110)-oriented GaAs quantum wells. The current measurements are performed by detecting the emitted Terahertz radiation at room temperature. The microscopic theory is based on a 14 x 14 k • p band-structure calculation in combination with the multi-subband semiconductor Bloch equations. For symmetric GaAs quantum wells grown in (110) direction, an oscillatory dependence of the injection currents on the exciting photon energy is obtained. The results of the microscopic theory are in good agreement with the measurements. }}, author = {{Duc, H. T. and Pochwala, M. and Förstner, Jens and Meier, Torsten and Priyadarshi, S. and Racu, A. M. and Pierz, K. and Siegner, U. and Bieler, M.}}, booktitle = {{Ultrafast Phenomena in Semiconductors and Nanostructure Materials XV}}, editor = {{Tsen, Kong-Thon and Song, Jin-Joo and Betz, Markus and Elezzabi, Abdulhakem Y.}}, keywords = {{tet_topic_qw}}, publisher = {{SPIE}}, title = {{{Injection currents in (110)-oriented GaAs/AlGaAs quantum wells: recent progress in theory and experiment}}}, doi = {{10.1117/12.876972}}, volume = {{7937}}, year = {{2011}}, } @article{4046, abstract = {{We demonstrate by spin quantum beat spectroscopy that in undoped symmetric (110)-oriented GaAs/AlGaAs single quantum wells, even a symmetric spatial envelope wave function gives rise to an asymmetric in-plane electron Land´e g-factor. The anisotropy is neither a direct consequence of the asymmetric in-plane Dresselhaus splitting nor a direct consequence of the asymmetric Zeeman splitting of the hole bands, but rather it is a pure higher-order effect that exists as well for diamond-type lattices. The measurements for various well widths are very well described within 14 × 14 band k·p theory and illustrate that the electron spin is an excellent meter variable for mapping out the internal—otherwise hidden—symmetries in two-dimensional systems. Fourth-order perturbation theory yields an analytical expression for the strength of the g-factor anisotropy, providing a qualitative understanding of the observed effects.}}, author = {{Hübner, J. and Kunz, S. and Oertel, S. and Schuh, D. and Pochwała, M. and Duc, H. T. and Förstner, Jens and Meier, Torsten and Oestreich, M.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{4}}, pages = {{041301(R)}}, publisher = {{American Physical Society (APS)}}, title = {{{Electron g-factor anisotropy in symmetric (110)-oriented GaAs quantum wells}}}, doi = {{10.1103/physrevb.84.041301}}, volume = {{84}}, year = {{2011}}, } @inproceedings{4042, abstract = {{A simulation environment for metallic nanostructures based on the Discontinuous Galerkin Time Domain method is presented. It is used to model optical transmission by silver bi‐chiral plasmonic crystals. The results of simulations qualitatively and quantitavely agree with experimental measurements of transmitted circular polarization.}}, author = {{Grynko, Yevgen and Förstner, Jens and Meier, Torsten and Radke, André and Gissibl, Timo and Braun, Paul V. and Giessen, Harald}}, editor = {{Chigrin, Dmitry N.}}, keywords = {{tet_topic_meta}}, number = {{1}}, pages = {{76--78}}, publisher = {{AIP}}, title = {{{Application of the Discontinuous Galerkin Time Domain Method to the Optics of Bi-Chiral Plasmonic Crystals}}}, doi = {{10.1063/1.3644217}}, volume = {{1398}}, year = {{2011}}, } @inproceedings{2194, author = {{Meyer, Björn and Plessl, Christian and Förstner, Jens}}, booktitle = {{Symp. on Application Accelerators in High Performance Computing (SAAHPC)}}, keywords = {{tet_topic_hpc}}, pages = {{60--63}}, publisher = {{IEEE Computer Society}}, title = {{{Transformation of scientific algorithms to parallel computing code: subdomain support in a MPI-multi-GPU backend}}}, doi = {{10.1109/SAAHPC.2011.12}}, year = {{2011}}, } @article{4129, abstract = {{We study a single quantum dot molecule doped with one electron in the presence of electron-phonon coupling. Both diagonal and off-diagonal interactions representing real and virtual processes with acoustic phonons via deformation potential and piezoelectric coupling are taken into account. We employ a non-perturbative quantum kinetic theory and show that the phonon-mediated relaxation is dominated by an electron tunneling on a picosecond time scale.A dependence of the relaxation on the temperature and the strength of the tunneling coupling is analyzed.}}, author = {{Grodecka-Grad, Anna and Förstner, Jens}}, issn = {{1742-6596}}, journal = {{Journal of Physics: Conference Series}}, keywords = {{tet_topic_qd}}, publisher = {{IOP Publishing}}, title = {{{Phonon-mediated relaxation in doped quantum dot molecules}}}, doi = {{10.1088/1742-6596/245/1/012035}}, volume = {{245}}, year = {{2010}}, } @article{4174, abstract = {{A quantum dot molecule doped with a single electron in the presence of diagonal and off-diagonal carrierphonon couplings is studied by means of a nonperturbative quantum kinetic theory. The interaction with acoustic phonons by deformation potential and piezoelectric coupling is taken into account. We show that the phonon-mediated relaxation is fast on a picosecond time scale and is dominated by the usually neglected off-diagonal coupling to the lattice degrees of freedom leading to phonon-assisted electron tunneling. We show that in the parameter regime of current electrical and optical experiments, the microscopic non-Markovian theory has to be employed.}}, author = {{Grodecka-Grad, A. and Förstner, Jens}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{11}}, publisher = {{American Physical Society (APS)}}, title = {{{Theory of phonon-mediated relaxation in doped quantum dot molecules}}}, doi = {{10.1103/physrevb.81.115305}}, volume = {{81}}, year = {{2010}}, } @article{4125, abstract = {{We numerically investigate the behavior of Whispering Gallery Modes (WGMs) in circularly shaped resonators like microdisks, with diameters in the range of optical vacuum wavelengths. The microdisk is embedded in an uniaxial anisotropic dielectric environment. By changing the optical anisotropy, one obtains spectral tunability of the optical modes. The degree of tunability strongly depends on the radial (azimuthal) mode order M (N). As the modes approach each other spectrally, anticrossing is observed, leading to a rearrangement of the optical states.}}, author = {{Declair, S. and Meier, Cedrik and Meier, Torsten and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_microdisk}}, number = {{4}}, pages = {{273--277}}, publisher = {{Elsevier BV}}, title = {{{Anticrossing of Whispering Gallery Modes in microdisk resonators embedded in an anisotropic environment}}}, doi = {{10.1016/j.photonics.2010.03.002}}, volume = {{8}}, year = {{2010}}, } @article{4177, abstract = {{Excitonic spectra of weakly disordered semiconductor heterostructures are simulated on the basis of a one-dimensional tight-binding model. The influence of the length scale of weak disorder in quantum wells on the redshift of the excitonic peak and its linewidth is studied. By calculating two-dimensional Fouriertransform spectra we are able to determine the contribution of disorder to inhomogeneous and also to homogeneous broadenings separately. This disorder-induced dephasing is related to a Fano-type coupling and leads to contributions to the homogeneous linewidth that depends on energy within the inhomogeneously broadened line. The model includes heavy- and light-hole excitons and yields smaller inhomogeneous broadening for the light-hole exciton if compared to the heavy-hole exciton, which agrees qualitatively with the experiment.}}, author = {{Kuznetsova, I. and Gőgh, N. and Förstner, Jens and Meier, Torsten and Cundiff, S. T. and Varga, I. and Thomas, P.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Modeling excitonic line shapes in weakly disordered semiconductor nanostructures}}}, doi = {{10.1103/physrevb.81.075307}}, volume = {{81}}, year = {{2010}}, } @article{4123, abstract = {{GaAs-based semiconductor microdisks with high quality whispering gallery modes (Q44000) have been fabricated.A layer of self-organized InAs quantumdots (QDs) served as a light source to feed the optical modes at room temperature. In order to achieve frequency tuning of the optical modes, the microdisk devices have been immersed in 4 – cyano – 4´-pentylbiphenyl (5CB), a liquid crystal(LC) with a nematic phase below the clearing temperature of TC≈34°C .We have studied the device performance in the temperature rangeof T=20-50°C, in order to investigate the influence of the nematic–isotropic phase transition on the optical modes. Moreover,we havea pplied an AC electric field to the device,which leads in the nematic phase to a reorientation of the anisotropic dielectric tensor of the liquid crystal.This electrical anisotropy can be used to achieve electrical tunability of the optical modes.Using the finite-difference time domain (FDTD) technique with an anisotropic material model, we are able to describe the influence of the liquid crystal qualitatively.}}, author = {{Piegdon, Karoline A. and Offer, Matthias and Lorke, Axel and Urbanski, Martin and Hoischen, Andreas and Kitzerow, Heinz-Siegfried and Declair, Stefan and Förstner, Jens and Meier, Torsten and Reuter, Dirk and Wieck, Andreas D. and Meier, Cedrik}}, issn = {{1386-9477}}, journal = {{Physica E: Low-dimensional Systems and Nanostructures}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{10}}, pages = {{2552--2555}}, publisher = {{Elsevier BV}}, title = {{{Self-assembled quantum dots in a liquid-crystal-tunable microdisk resonator}}}, doi = {{10.1016/j.physe.2009.12.051}}, volume = {{42}}, year = {{2010}}, } @article{4169, abstract = {{It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed. A microscopic theoretical analysis shows that this current reversal is caused by the coupling of the light- and heavy-hole bands and that the hole currents dominate the overall current response. These surprising consequences of band mixing illuminate fundamental physics as they are unique for experiments which are able to monitor electronic transport resulting from carriers with relatively large momenta.}}, author = {{Priyadarshi, S. and Racu, A. M. and Pierz, K. and Siegner, U. and Bieler, M. and Duc, H. T. and Förstner, Jens and Meier, Torsten}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_qw}}, number = {{21}}, publisher = {{American Physical Society (APS)}}, title = {{{Reversal of Coherently Controlled Ultrafast Photocurrents by Band Mixing in Undoped GaAs Quantum Wells}}}, doi = {{10.1103/physrevlett.104.217401}}, volume = {{104}}, year = {{2010}}, } @inproceedings{4167, abstract = {{The electromagnetic field in the vicinity of sharp edges needs a special treatment in numeric calculation whenever accurate, fast converging results are necessary. One of the fundamental works concerning field singularities has been proposed in 1972 [1] and states that the electromagnetic energy density must be integrable over any finite domain, even if this domain contains singularities. It is shown, that the magnetic field H(, ϕ) and electric field E(, ϕ) are proportional to ∝ (t−1) for  → 0. The variable  is the distance to the edge and t has to fulfill the integrability condition and thus is restricted to 0 < t < 1. This result is often used to reduce the error corresponding to the singularity without increasing the numerical effort [2 - 5]. For this purpose, a correction factor K is estimated by inserting the proportionality into the wave equation. It is shown, that this method improves the accuracy of the result significantly, however the order of convergence is often not studied. In [4] a method to modify the material parameters in order to use analytic results to improve the numeric calculation is presented. In this contribution we will - inspired by the scheme given in [4] - develop a new method to estimate a correction factor for perfect conducting materials (PEC) and demonstrate the improvement of the results compared to the standard edge correction. Therefore analytic results (comparable to [1]) are consequently merged with the scheme in [4]. The main goal of this work is the calculation of the second harmonic generation (SHG) in the wave response of so-called metamaterials [6]. Frequently these structures contain sharp metallic edges with field singularities at the interfaces which have a strong impact on the SHG signals. Thus, an accurate simulation of singularities is highly important. However, the following approach can also be applied to many other setups, and one of them is shown in the example below.}}, author = {{Classen, C and Förstner, Jens and Meier, Torsten and Schuhmann, R}}, booktitle = {{2010 IEEE Antennas and Propagation Society International Symposium}}, isbn = {{9781424449675}}, keywords = {{tet_topic_numerics}}, location = {{Toronto, ON, Canada}}, publisher = {{IEEE}}, title = {{{Enhanced FDTD edge correction for nonlinear effects calculation}}}, doi = {{10.1109/aps.2010.5562017}}, year = {{2010}}, } @article{4172, abstract = {{Microdisks made from GaAs with embedded InAs quantum dots are immersed in the liquid crystal 4-cyano-4’-pentylbiphenyl (5CB). The quantum dots serve as emitters feeding the optical modes of the photonic cavity. By changing temperature, the liquid crystal undergoes a phase transition from the isotropic to the nematic state, which can be used as an effective tuning mechanism of the photonic modes of the cavity. In the nematic state, the uniaxial electrical anisotropy of the liquid crystal molecules can be exploited for orienting the material in an electric field, thus externally controlling the birefringence of the material. Using this effect, an electric field induced tuning of the modes is achieved. Numerical simulations using the finite-differences time-domain (FDTD) technique employing an anisotropic dielectric medium allow to understand the alignment of the liquid crystal molecules on the surface of the microdisk resonator.}}, author = {{Piegdon, Karoline A. and Declair, Stefan and Förstner, Jens and Meier, Torsten and Matthias, Heiner and Urbanski, Martin and Kitzerow, Heinz-Siegfried and Reuter, Dirk and Wieck, Andreas D. and Lorke, Axel and Meier, Cedrik}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{8}}, publisher = {{The Optical Society}}, title = {{{Tuning quantum-dot based photonic devices with liquid crystals}}}, doi = {{10.1364/oe.18.007946}}, volume = {{18}}, year = {{2010}}, } @article{4127, abstract = {{The dynamics of charge and spin injection currents excited by circularly polarized, one-color laser beams in semiconductor quantum wells is analyzed. Our microscopic approach is based on a 14x14 k · p band-structure theory in combination with multisubband semiconductor Bloch equations which allows a detailed analysis of the photogenerated carrier distributions and coherences in k space. Charge and spin injection currents are numerically calculated for [110]- and [001]-grown GaAs quantum wells including dc population contributions and ac contributions that arise from intersubband coherences. The dependencies of the injection currents on the excitation conditions, in particular, the photon energy are computed and discussed.}}, author = {{Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{11}}, publisher = {{American Physical Society (APS)}}, title = {{{Microscopic analysis of charge and spin photocurrents injected by circularly polarized one-color laser pulses in GaAs quantum wells}}}, doi = {{10.1103/physrevb.82.115316}}, volume = {{82}}, year = {{2010}}, } @inproceedings{4176, abstract = {{A microscopic theory that describes injection currents in GaAs quantum wells is presented. 14 × 14 band k.p theory is used to compute the band structure including anisotropy and spin-orbit interaction. Transient injection currents are obtained via numerical solutions of the semiconductor Bloch equations. Depending on the growth direction of the considered quantum well system and the propagation and polarization directions of the incident light beam, it is possible to generate charge and/or spin photocurrents on ultrashort time scales. The dependence of the photocurrents on the excitation conditions is computed and discussed.}}, author = {{Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIV}}, editor = {{Song, Jin-Joo and Tsen, Kong-Thon and Betz, Markus and Elezzabi, Abdulhakem Y.}}, keywords = {{tet_topic_qw}}, pages = {{76000S--76000S--9}}, publisher = {{SPIE}}, title = {{{Microscopic theoretical analysis of optically generated injection currents in semiconductor quantum wells}}}, doi = {{10.1117/12.840388}}, volume = {{7600}}, year = {{2010}}, } @inproceedings{4180, abstract = {{We show that an optically driven carrier spin undergoes indirect dephasing even in the absence of spin-reservoir coupling and illustrate it for phonon-induced decoherence during optical spin rotation in a single quantum dot.}}, author = {{Grodecka, Anna and Machnikowski, Pawel and Förstner, Jens}}, booktitle = {{Advances in Optical Sciences Congress}}, isbn = {{9781557528735}}, keywords = {{tet_topic_qd}}, publisher = {{OSA Technical Digest (CD) (Optical Society of America, 2009)}}, title = {{{Indirect Dephasing Channel for Optically Controlled Spin in a Single Quantum Dot}}}, doi = {{10.1364/nlo.2009.nma1}}, year = {{2009}}, } @article{4182, abstract = {{We demonstrate that an optically driven spin of a carrier in a quantum dot undergoes indirect dephasing via conditional optically induced charge evolution even in the absence of any direct interaction between the spin and its environment. A generic model for the indirect dephasing with a three-component system with spin, charge, and reservoir is proposed. This indirect decoherence channel is studied for the optical spin manipulation in a quantum dot with a microscopic description of the charge-phonon interaction taking into account its non-Markovian nature.}}, author = {{Grodecka, A. and Machnikowski, P. and Förstner, Jens}}, issn = {{1050-2947}}, journal = {{Physical Review A}}, keywords = {{tet_topic_qd}}, number = {{4}}, publisher = {{American Physical Society (APS)}}, title = {{{Indirect spin dephasing via charge-state decoherence in optical control schemes in quantum dots}}}, doi = {{10.1103/physreva.79.042331}}, volume = {{79}}, year = {{2009}}, } @inproceedings{4181, abstract = {{We experimentally and theoretically investigate microdisk resonators with embedded quantum dots immersed in a liquid crystal in its nematic phase, showing the tunabililty of the photonic modes via external parameters like temperature or electric field.}}, author = {{Förstner, Jens and Meier, Cedrik and Piegdon, Karoline and Declair, Stefan and Hoischen, Andreas and Urbanski, Mark and Meier, Torsten and Kitzerow, Heinz-Siegfried}}, booktitle = {{Advances in Optical Sciences Congress}}, isbn = {{9781557528735}}, keywords = {{tet_topic_microdisk}}, location = {{Honolulu, Hawaii United States}}, publisher = {{OSA Technical Digest (CD) (Optical Society of America, 2009), paper NTuC2}}, title = {{{Coupling Dynamics of Quantum Dots in a Liquid-Crystal-Tunable Microdisk Resonator}}}, doi = {{10.1364/nlo.2009.ntuc2}}, year = {{2009}}, } @inproceedings{4179, abstract = {{We numerically investigate Whispering Gallery Modes (WGM) in a subwavelength microdisk resonator [1] embedded in an uniaxial anisotropic liquid crystal environment. It is shown that the WGMs have anticrossing behavior when modes of different radial mode order M or azimuthal order N approach each other spectrally. }}, author = {{Förstner, Jens and Declair, S. and Meier, Cedrik and Meier, Torsten}}, booktitle = {{Theoretical and Computational Nanophotonics Tacona-Photonics}}, keywords = {{tet_topic_microdisk}}, location = {{Tacona}}, number = {{1}}, pages = {{60--62}}, title = {{{Anticrossing of Whispering Gallery Modes in Microdisk Resonators Embedded in a Liquid Crystal}}}, doi = {{10.1063/1.3253921}}, volume = {{1176}}, year = {{2009}}, } @inproceedings{4184, abstract = {{We have experimentally investigated injection currents generated by all-optical excitation of GaAs/AlGaAs quantum wells excited with 130 fs optical pulses. The currents have been detected via free-space THz experiments at room temperature. Our experiments prove that Coulomb effects strongly influence injection currents. This becomes most prominently visible when exciting light-hole exciton transitions. At this photon energy we observe a pronounced phase shift of the current transients which is due to oppositely oriented heavy-hole and light-hole type contributions. We are currently developing a microscopic theory based on a 14×14 k.p model in combination with the semiconductor Bloch equations to describe the observed features quantitatively. The combined theoretical and experimental approach will allow us to analyze the influence of the bandstructure and interaction effects on the injection current amplitude and current dynamics.}}, author = {{Bieler, M. and Pierz, K. and Siegner, U. and Dawson, P. and Duc, H. T. and Förstner, Jens and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIII}}, editor = {{Tsen, Kong-Thon and Song, Jin-Joo and Betz, Markus and Elezzabi, Abdulhakem Y.}}, keywords = {{tet_topic_qw}}, location = {{San Jose (California / USA)}}, pages = {{721404--721404--13}}, publisher = {{SPIE}}, title = {{{Generation of injection currents in (110)-oriented GaAs quantum wells: experimental observation and development of a microscopic theory}}}, doi = {{10.1117/12.811841}}, volume = {{7214}}, year = {{2009}}, } @article{4187, abstract = {{We study phonon-assisted electron tunneling in semiconductor quantum dot molecules. In particular, singletsinglet relaxation in a two-electron-doped structure is considered. The influence of Coulomb interaction is discussed via comparison with a single-electron system. We find that the relaxation rate reaches similar values in the two cases but the Coulomb interaction shifts the maximum rates toward larger separations between the dots. The difference in electron-phonon interaction between deformation potential and piezoelectric coupling is investigated. We show that the phonon-induced tunneling between two-electron singlet states is a fast process, taking place on the time scales of the order of a few tens of picoseconds.}}, author = {{Grodecka, A. and Machnikowski, P. and Förstner, Jens}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{8}}, publisher = {{American Physical Society (APS)}}, title = {{{Phonon-assisted tunneling between singlet states in two-electron quantum dot molecules}}}, doi = {{10.1103/physrevb.78.085302}}, volume = {{78}}, year = {{2008}}, } @article{4256, abstract = {{We present phase-resolved pulse propagation measurements that allow us to fully describe the transition between several light–matter interaction regimes. The complete range from linear excitation to the breakdown of the photonic bandgap on to self-induced transmission and self-phase modulation is studied on a high-quality multiple-quantum-well Bragg structure. An improved fast-scanning cross-correlation frequency-resolved optical gating setup is applied to retrieve the pulse phase with an excellent signal-tonoise ratio. Calculations using the semiconductor Maxwell–Bloch equations show qualitative agreement with the experimental findings. }}, author = {{zu Siederdissen, Tilman Höner and Nielsen, Nils C. and Kuhl, Jürgen and Schaarschmidt, Martin and Förstner, Jens and Knorr, Andreas and Khitrova, Galina and Gibbs, Hyatt M. and Koch, Stephan W. and Giessen, Harald}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{tet_topic_polariton, tet_topic_qw}}, number = {{11}}, publisher = {{The Optical Society}}, title = {{{Transition between different coherent light–matter interaction regimes analyzed by phase-resolved pulse propagation}}}, doi = {{10.1364/ol.30.001384}}, volume = {{30}}, year = {{2008}}, } @article{4317, abstract = {{Phonon-assisted singlet-singlet relaxation in semiconductor quantum dot molecules is studied theoretically. Laterally coupled quantum dot structures doped with two electrons are considered. We take into account interaction with acoustic phonon modes via deformation potential and piezoelectric coupling. We show that piezoelectric mechanism for the considered system is of great importance and for some ranges of quantum dot molecule parameters is the dominant contribution to relaxation. It is shown that the phonon-assisted tunneling is much faster (down to ∼ 6 ps even at zero temperature) in comparison with other decoherence processes. The influence of Coulomb interaction is discussed and its consequences are indicated. We calculate the relaxation rates for GaAs quantum dot molecules and study the dependence on quantum dot size, distance and offset between the constituent quantum dots. In addition the temperature dependence of the tunneling rates is analyzed.}}, author = {{Grodecka, Anna and Machnikowski, Paweł and Förstner, Jens}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qd}}, number = {{2}}, pages = {{474--478}}, publisher = {{Wiley}}, title = {{{Theoretical study of phononassisted singlet-singlet relaxation in two-electron semiconductor quantum dot molecules}}}, doi = {{10.1002/pssc.200880319}}, volume = {{6}}, year = {{2008}}, } @article{4303, abstract = {{The interaction of strong low-area pulses with two-level systems shows absorption line narrowing and hole burning within the homogeneous linewidth as a result of nonlinear wave mixing. The wave mixing results from the two-level electronic saturation nonlinearity and occurs, depending on the sign of the pulse area, as a strong absorption enhancement or gain at the transition frequency of the two-level system for resonant excitation.}}, author = {{Förstner, Jens and Knorr, A. and Lindberg, M. and Koch, S. W.}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{tet_topic_polariton}}, number = {{20}}, publisher = {{The Optical Society}}, title = {{{Line narrowing and hole burning within the homogeneous linewidth: a new wave-mixing effect in two-level systems}}}, doi = {{10.1364/ol.27.001830}}, volume = {{27}}, year = {{2007}}, } @article{4189, abstract = {{We theoretically study the biexciton-phonon interaction in strongly confined semiconductor quantum dots. For spectrally narrow single-pulse excitation generation of biexcitonic occupations is only possible via a two-photon cascade, which exhibits renormalized Rabi oscillations and spectrally compressed phononsidebands.}}, author = {{Förstner, Jens and Knorr, A. and Moloney, J. V.}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qd}}, number = {{7}}, pages = {{2389--2392}}, publisher = {{Wiley}}, title = {{{Interplay of electron-phonon and Coulomb interaction in semiconductor quantum dots}}}, doi = {{10.1002/pssc.200668111}}, volume = {{3}}, year = {{2006}}, } @inproceedings{4241, abstract = {{We discuss second-harmonic generation experiments on planar arrays of magnetic split-ring resonators, using 150 fs pulses at 1.5 mum wavelength. Lithographic tuning reveals by far the largest signals when exciting the magnetic-dipole resonance.}}, author = {{Klein, M. W. and Enkrich, C. and Wegener, M. and Förstner, Jens and Moloney, J. V. and Hoyer, W. and Stroucken, T. and Meier, Torsten and Koch, S. W. and Linden, S.}}, booktitle = {{2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference}}, isbn = {{9781557528131}}, issn = {{2160-9004 }}, keywords = {{tet_topic_meta}}, location = {{Long Beach, CA (USA)}}, publisher = {{IEEE}}, title = {{{Optical experiments on second-harmonic generation from metamaterials consisting of split-ring resonators}}}, doi = {{10.1109/cleo.2006.4629006}}, year = {{2006}}, } @article{4243, abstract = {{We investigate the optical properties of a Coulomb-coupled double-quantum dot system excited by coherent light pulses. Basic effects of Coulomb coupling regarding linear and nonlinear optical processes are discussed. By numerically solving the Heisenberg equation of motion we are able to present the temporal evolution of the system’s density matrix for a wide range of coupling parameters. The two main coupling effects in dipole approximation, biexcitonic shift and Förster energy transfer, are investigated and their qualitative and quantitative influence on absorption spectra, Rabi oscillations, and single- and two-pulse excitation is discussed. We present simulated differential transmission spectra to allow for comparison with recent experimental studies.}}, author = {{Danckwerts, J. and Ahn, K. J. and Förstner, Jens and Knorr, A.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{16}}, pages = {{165318--165318--18}}, publisher = {{American Physical Society (APS)}}, title = {{{Theory of ultrafast nonlinear optics of Coulomb-coupled semiconductor quantum dots: Rabi oscillations and pump-probe spectra}}}, doi = {{10.1103/physrevb.73.165318}}, volume = {{73}}, year = {{2006}}, } @inproceedings{4191, abstract = {{We study optical second-harmonic generation from planar arrays of magnetic split-ring resonators at 1.5 microns resonance wavelength. We obtain by far the largest signals when exciting the magnetic-dipole resonance. }}, author = {{Klein, Matthias W. and Enkrich, Christian and Wegener, Martin and Förstner, Jens and Moloney, Jerome V. and Hoyer, Walter and Stroucken, Tineke and Meier, Torsten and Koch, Stephan W. and Linden, Stefan}}, booktitle = {{Photonic Metamaterials: From Random to Periodic}}, isbn = {{155752808X}}, keywords = {{tet_topic_meta}}, publisher = {{OSA}}, title = {{{Optical Experiments on Second-Harmonic Generation with Metamaterials Composed of Split-Ring Resonators}}}, doi = {{10.1364/meta.2006.tuc5}}, year = {{2006}}, } @inproceedings{4247, abstract = {{We numerically investigate strong light-matter interaction and normal mode coupling/splitting in a system composed of a single two-level atom and the localized mode of a small mode volume photonic crystal nanocavity.}}, author = {{Förstner, Jens and Dineen, Colm and Zakharian, A.R. and Moloney, Jerome V. and Koch, Stephan W.}}, booktitle = {{Frontiers in Optics}}, isbn = {{1557527970}}, publisher = {{OSA}}, title = {{{Normal Mode Coupling in Photonic Crystal Nanocavities}}}, doi = {{10.1364/fio.2005.fwc2}}, year = {{2005}}, } @article{4249, abstract = {{The interaction of electrons with LO phonons provides an important mechanism of optical dephasing and carrier scattering for the two-dimensional electron gas in semiconductor quantum wells. In this paper, the corresponding ultrafast nonlinearities for off-resonant and resonant intersubband excitations are investigated. Quantum kinetic effects of the electron-phonon interaction and the corresponding violation of the microscopic energy conservation yield a qualitative different picture compared to the standard Markovian theory, if the phonon energy is larger than the intersubband-gap energy.}}, author = {{Butscher, Stefan and Förstner, Jens and Waldmüller, Inès and Knorr, Andreas}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{4}}, pages = {{045314--045314--4}}, publisher = {{American Physical Society (APS)}}, title = {{{Ultrafast electron-phonon interaction of intersubband transitions: Quantum kinetics from adiabatic following to Rabi-oscillations}}}, doi = {{10.1103/physrevb.72.045314}}, volume = {{72}}, year = {{2005}}, } @inproceedings{4251, abstract = {{A system of two quantum dots coupled by dipole‐dipole interaction is investigated within a density matrix approach. We compute the temporal evolution of the system in the linear and nonlinear optical regime and discuss the possibility of performing basic quantum information gates. The influence of the Förster energy transfer on Rabi oscillations is discussed.}}, author = {{Danckwerts, J. and Förstner, Jens and Knorr, A.}}, booktitle = {{AIP Conference Proceedings}}, issn = {{0094-243X}}, keywords = {{tet_topic_qd}}, publisher = {{AIP}}, title = {{{Quantum information processing using Coulomb-coupled quantum dots}}}, doi = {{10.1063/1.1994668}}, volume = {{772}}, year = {{2005}}, } @article{4252, abstract = {{The electromagnetic field of a high-quality photonic crystal nanocavity is computed using the finite difference time domain method. It is shown that a separatrix occurs in the local energy flux discriminating between predominantly near and far field components. Placing a two-level atom into the cavity leads to characteristic field modifications and normalmode splitting in the transmission spectra.}}, author = {{Dineen, C. and Förstner, Jens and Zakharian, A.R. and Moloney, J.V. and Koch, S.W.}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_phc}}, number = {{13}}, publisher = {{The Optical Society}}, title = {{{Electromagnetic field structure and normal mode coupling in photonic crystal nanocavities}}}, doi = {{10.1364/opex.13.004980}}, volume = {{13}}, year = {{2005}}, } @article{4254, abstract = {{A microscopic description based on the density matrix formalism is developed to describe the dynamics of photoemission of hot electrons at semiconductor surfaces, including the interaction of bulk and surface states. The equations of motion for the electronic occupations and transitions include the interaction with arbitrary optical fields as well as the electron-phonon coupling. Model wave functions are used to qualitatively describe the bulk-surface dynamics and the subsequent time resolved two-photon photoemission s2PPEd spectra. Our results suggest that it is possible to extract energetic and temporal information of the underlying dynamical occupations of the intermediate states from the 2PPE spectra.}}, author = {{Zeiser, A. and Bücking, N. and Förstner, Jens and Knorr, A.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, number = {{24}}, publisher = {{American Physical Society (APS)}}, title = {{{Microscopic theory of electron dynamics and time-resolved two-color two-photon photoemission at semiconductor surfaces}}}, doi = {{10.1103/physrevb.71.245309}}, volume = {{71}}, year = {{2005}}, } @inproceedings{4258, abstract = {{A theoretical description of ultrafast phonon induced electronic transport between surface and bulk states after optical excitation is presented. In particular, the influence of the electron transfer processes on two photon photo emission is evaluated. }}, author = {{Bucking, N. and Zeiser, A. and Förstner, Jens and Knorr, A.}}, booktitle = {{2005 Quantum Electronics and Laser Science Conference}}, isbn = {{1557527962}}, pages = {{1929--1931}}, publisher = {{IEEE}}, title = {{{Kinetic theory of the electron transport in the two photon photo emission at semiconductor surfaces}}}, doi = {{10.1109/qels.2005.1549331}}, year = {{2005}}, } @inproceedings{4259, abstract = {{The ultrafast intersubband dynamics in a semiconductor quantum well subband system is investigated theoretically. Non-Markovian electron-phonon interaction leads to polaron formation and enhanced dephasing. }}, author = {{Butscher, S. and Förstner, Jens and Waldmuller, I. and Knorr, A.}}, booktitle = {{2005 Quantum Electronics and Laser Science Conference}}, isbn = {{1557527962}}, pages = {{640--642}}, publisher = {{IEEE}}, title = {{{Ultrafast quantum kinetics of semiconductor intersubband transitions: polaron signatures and dephasing dynamics}}}, doi = {{10.1109/qels.2005.1548881}}, year = {{2005}}, } @article{4260, abstract = {{Using a fully quantized description of strongly confined electrons interacting with acoustic phonons and the photon field, the nonstationary resonance-fluorescence spectra of a semiconductor quantum dot are investigated. For excitation pulses with durations approaching typical electron-phonon scattering times, the virtual quantum processes yield an observable electron-phonon sideband broadening.}}, author = {{Ahn, K. J. and Förstner, Jens and Knorr, A.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{15}}, publisher = {{American Physical Society (APS)}}, title = {{{Resonance fluorescence of semiconductor quantum dots: Signatures of the electron-phonon interaction}}}, doi = {{10.1103/physrevb.71.153309}}, volume = {{71}}, year = {{2005}}, } @article{4262, abstract = {{Time-dependent two-photon photoemission spectra are used to resolve the femtosecond dynamics of hot electrons at the energetically lowest surface resonance of reconstructed InP(100). Two different cases are studied, where electrons either are lifted into the surface resonance via a direct optical transition or are captured from bulk states. These data are the first of this kind recorded with a time resolution below 70 fs. The microscopic analysis shows that electron-phonon scattering is a major mechanism for electron transfer between surface and bulk states.}}, author = {{Töben, L. and Gundlach, L. and Ernstorfer, R. and Eichberger, R. and Hannappel, T. and Willig, F. and Zeiser, A. and Förstner, Jens and Knorr, A. and Hahn, P. H. and Schmidt, W. G.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, number = {{6}}, publisher = {{American Physical Society (APS)}}, title = {{{Femtosecond Transfer Dynamics of Photogenerated Electrons at a Surface Resonance of Reconstructed InP(100)}}}, doi = {{10.1103/physrevlett.94.067601}}, volume = {{94}}, year = {{2005}}, } @article{4264, abstract = {{We demonstrate that the temporal pulse phase remains essentially unaltered before separate phase characteristics are developed when propagating high-intensity pulses coherently on the exciton resonance of an optically thick semiconductor. This behavior is a clear manifestation of self-induced transmission and pulse breakup into solitonlike pulses due to Rabi flopping of the carrier density. Experiments using a novel fast-scan cross-correlation frequency-resolved optical gating (XFROG) method are in good agreement with numerical calculations based on the semiconductor Bloch equations.}}, author = {{Nielsen, N. C. and zu Siederdissen, T. Höner and Kuhl, J. and Schaarschmidt, M. and Förstner, Jens and Knorr, A. and Giessen, H.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_qd}}, number = {{5}}, publisher = {{American Physical Society (APS)}}, title = {{{Phase Evolution of Solitonlike Optical Pulses during Excitonic Rabi Flopping in a Semiconductor}}}, doi = {{10.1103/physrevlett.94.057406}}, volume = {{94}}, year = {{2005}}, } @inbook{4269, abstract = {{We investigate the spatiotemporal characteristics of subpicosecond pulse propagation in the nonlinear defocusing regime below the band edge of bulk GaAs. We observe temporal and spatial pulse compression and instabilities.}}, author = {{Nielsen, N. C. and zu Höner Siederdissen, T. and Kuhl, J. and Schaarschmidt, M. and Förstner, Jens and Knorr, A. and Koch, S. W. and Giessen, H.}}, booktitle = {{Springer Series in Chemical Physics}}, isbn = {{9783540241102}}, issn = {{0172-6218}}, keywords = {{tet_topic_polariton}}, pages = {{19--21}}, publisher = {{Springer Berlin Heidelberg}}, title = {{{Temporal and Spatial Pulse Compression in a Nonlinear Defocusing Material}}}, doi = {{10.1007/3-540-27213-5_5}}, year = {{2005}}, } @article{4270, abstract = {{The adiabatic driving of the resonant electron dynamics in a one-dimensional resonant photonic band gap is proposed as an optical mechanism for nonlinear ultrafast switching. Pulsed excitation inside the photonic gap results in an ultrafast suppression and recovery of the gap. This behavior results from the adiabatic carrier dynamics due to rapid radiative damping inside the band gap.}}, author = {{Schaarschmidt, Martin and Förstner, Jens and Knorr, Andreas and Prineas, John P. and Nielsen, Nils C. and Kuhl, Jürgen and Khitrova, Galina and Gibbs, Hyatt M. and Giessen, Harald and Koch, Stephan W.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{23}}, publisher = {{American Physical Society (APS)}}, title = {{{Adiabatically driven electron dynamics in a resonant photonic band gap: Optical switching of a Bragg periodic semiconductor}}}, doi = {{10.1103/physrevb.70.233302}}, volume = {{70}}, year = {{2004}}, } @article{4274, abstract = {{We present a theory of the optical line shape of coherent intersubband transitions in a semiconductor quantum well, considering non-Markovian LO-phonon scattering as major broadening mechanism. We show that a quantum kinetic approach leads to additional polaron resonances and a resonance enhancement for gap energies close to the phonon energy.}}, author = {{Butscher, S. and Förstner, Jens and Waldmüller, I. and Knorr, A.}}, issn = {{0370-1972}}, journal = {{physica status solidi (b)}}, keywords = {{tet_topic_qw}}, number = {{11}}, pages = {{R49--R51}}, publisher = {{Wiley}}, title = {{{Polaron signatures in the line shape of semiconductor ;intersubband transitions: quantum kinetics of the electron–phonon interaction}}}, doi = {{10.1002/pssb.200409053}}, volume = {{241}}, year = {{2004}}, } @article{4277, abstract = {{We investigate the temporal and spectral properties of subpicosecond pulses transmitted on the heavy-hole exciton transition through a multiple-quantum-well Bragg structure, exhibiting a one-dimensional photonic band gap. At low light intensities, a temporal propagation beating is observed. This beating is strongly dependent on the optical dephasing time T2 which is dominated by the radiative interwell coupling. In an intermediate intensity regime, the Pauli-blocking nonlinearity leads to gradual suppression of the photonic band gap and vanishing of the linear propagation beating. For highly nonlinear excitation, we find signatures of selfinduced transmission due to Rabi flopping and adiabatic following of the carrier density. Numerical simulations using the semiconductor Maxwell-Bloch equations are in excellent agreement with the experimental data up to intensities for which higher many-particle correlations become more important and self-phase modulation occurs in the sample substrate.}}, author = {{Nielsen, N. C. and Kuhl, J. and Schaarschmidt, M. and Förstner, Jens and Knorr, A. and Koch, S. W. and Khitrova, G. and Gibbs, H. M. and Giessen, H.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Linear and nonlinear pulse propagation in a multiple-quantum-well photonic crystal}}}, doi = {{10.1103/physrevb.70.075306}}, volume = {{70}}, year = {{2004}}, } @inproceedings{4279, abstract = {{We demonstrate temporal and spatial pulse compression and modulational instabilities in the nonlinear defocusing regime near the band edge of bulk GaAs. Experiment and theory show that spatiotemporal coupling is responsible for these surprising phenomena.}}, author = {{Nielsen, Nils. C. and Siederdissen, Tilmann H. zu and Kuhl, Jürgen and Schaarschmidt, Martin and Förstner, Jens and Knorr, Andreas and Koch, Stephan W. and Giessen, Harald }}, booktitle = {{International Conference on Ultrafast Phenomena 2004}}, isbn = {{3-54024-110-8}}, keywords = {{tet_topic_polariton}}, location = {{Niigata (Japan)}}, publisher = {{Technical Digest (CD) (Optical Society of America, 2004)}}, title = {{{Subpicosecond spatiotemporal pulse compression in a nonlinear defocusing material}}}, year = {{2004}}, } @inproceedings{4280, abstract = {{Theoretically and experimentally, we investigate temporal phase evolution during Rabi-flopping on the A-exciton resonance in CdSe using a novel fast-scanning XFROG method and observe phase changes smaller than π/2 compared to the slightly-chirped input pulse.}}, author = {{Höner zu Siederdissen, Tilman and Nielsen, Nils Christian. and Kuhl, Jürgen and Förstner, Jens and Knorr, Andreas and Giessen, Harald}}, booktitle = {{International Quantum Electronics Conference and Photonic Applications Systems Technologies}}, isbn = {{1-55752-770-9}}, keywords = {{tet_topic_qd}}, location = {{San Francisco, California (USA)}}, publisher = {{OSA}}, title = {{{Temporal phase evolution during excitonic Rabi flopping in semiconductors}}}, doi = {{10.1364/iqec.2004.imb3}}, year = {{2004}}, } @inproceedings{4281, abstract = {{The coupled spatiotemporal characteristics of subpicosecond pulses propagating in the nonlinear defocusing regime near the band edge of bulk GaAs are investigated experimentally and theoretically. We demonstrate pulse compression both in time and transverse space.}}, author = {{Nielsen, Nils C. and Kuhl, Jürgen and Schaarschmidt, Martin and Förstner, Jens and Knorr, Andreas and Koch, Stephan W. and Giessen, Harald }}, booktitle = {{Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies}}, isbn = {{1-55752-770-9}}, keywords = {{tet_topic_polariton}}, location = {{San Francisco, California (USA)}}, publisher = {{Technical Digest (CD) (Optical Society of America, 2004)}}, title = {{{Temporal and spatial compression of near-resonant pulses in a nonlinear defocusing semiconductor }}}, year = {{2004}}, } @inproceedings{4282, abstract = {{We investigate theoretically the ultrafast nonlinear suppression of the resonant photonic band gap by strong laser pulses in semiconductor multiple qnantum wells. We achieve good agreement with our measurements on reflection samples.}}, author = {{Schaarschmidt, Martin and Förstner, Jens and Knorr, Andreas and Prineas, John P. and Nielsen, Nils C. and Kuhl, Jürgen and Kithrova, Galina and Gibbs, Hyatt M. and Giessen, Harald and Koch, Stephan W.}}, booktitle = {{Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies}}, isbn = {{1-55752-778-4 }}, keywords = {{tet_topic_qw}}, location = {{San Francisco, California (USA) }}, publisher = {{OSA}}, title = {{{Nonlinear light pulse propagation in Bragg-periodic multiple semiconductor quantum well samples: ultrafast switching of a resonant photonic band gap}}}, doi = {{10.1364/iqec.2004.iwa3}}, year = {{2004}}, } @inbook{4286, abstract = {{Due to their many-particle character and their application in quantum cascade lasers, optical intersubband excitations in semiconductor quantum wells have become the focus of many recent publications [1,2]. In samples of high quality, intrinsic processes like electron-electron and electron-phonon many particle correlations determine the basic optical and transport properties such as lineshape and ultrafast dynamics. At the same time, intersubband excitations allow the direct investigation of dynamical properties of an important model system of many particle physics - the two-dimensional electron gas. We here present a microscopic theory for the intersubband dynamics and absorption. The calculation of absorption spectra of MQW systems is in principle composed of two parts: the determination of the polarization in a single quantum well within a density matrix approach as the source of electromagnetic radiation (Fig. 1a) and the calculation of the generated fields in the geometry of interest (Fig. 1b) within a Green's function approach [3,4]. We will here focus on the so-called single-pass geometry (cf. Fig. 1b, [5]).}}, author = {{Waldmüller, Ines and Förstner, Jens and Knorr, Andreas }}, booktitle = {{Nonequilibrium Physics at Short Time Scales}}, editor = {{Morawetz, Klaus}}, isbn = {{9783642057458}}, keywords = {{tet_topic_qw}}, publisher = {{Springer Berlin Heidelberg}}, title = {{{Self-consistent Projection Operator Theory of Intersubband Absorbance in Semiconductor Quantum Wells}}}, doi = {{10.1007/978-3-662-08990-3}}, year = {{2004}}, } @phdthesis{4319, abstract = {{In dieser Arbeit wird eine Theorie vorgestellt, welche die quantenmechanische Vielteilchenphysik der Licht-Materie Wechselwirkung in Halbleiternanostrukturen beschreibt. Diese mikroskopische Beschreibung wird durch Kombination eines allgemeinen Dichtematrixansatzes mit speziellen Methoden zur Auswertung der Maxwellgleichungen wie der zeitaufgelösten Finite-Differenzen-Methode (FDTD) erreicht. Die Theorie wird auf verschiedene physikalische Situationen angewendet, wie z.B. Lichtausbreitung in Volumenhalbleitern, Interband- und Intersubbandübergänge in Quantenfilmstrukturen und optische Anregung von Quantenpunkten. Der Fokus liegt dabei auf der Beschreibung der linearen und nichtlinearen Antwort des Vielteilchensystems und seiner Ankopplung an das elektromagnetische Feld. In diesem Zusammenhang wird sowohl die Erzeugung als auch der Zerfall von optischen Anregungen untersucht, indem verschiedene Kopplungsmechanismen wie Elektron-Phonon-, Elektron-Photon- und Elektron-Elektron-Wechselwirkung berücksichtigt werden. Im Bereich der linearen Optik, also für Anregung mit geringer Intensität, ermöglicht die Theorie die Berechnung von Absorptionsspektren. Verschiedene Effekte in linearer Optik werden in dieser Arbeit untersucht und beschrieben: Linienaufspaltung durch Polaritonen im Volumenmaterial, Zunahme der Linienbreite bei Intersubbandübergängen verursacht durch Elektron-Elektron- und Elektron- Phonon-Streuung in einzelnen Quantenfilmen, Bildung einer optischen Bandlücke durch starke radiative Kopplung in Vielfilmstrukturen in Bragg-Geometrie, Phononenseitenbänder verursacht durch quantenkinetische Effekte in einzelnen Quantenpunkten und schliesslich Superradianz und Interferenzeffekte in Quantenpunktgittern. Bei nichtlinearer Anregung treten Dichte-Rabiflops als fundamentale Prozesse in allen betrachteten Systemen auf und können als kohärente Be- und Entvölkerung von quantenmechanischen Zuständen beobachtet werden. Der Einfluss von starker Lichtkopplung und verschiedenen Wechselwirkungen auf dynamische Größen wie die Besetzung wird untersucht. Bei nichtlinearer Propagation, bei der sich ein starker Lichtpuls über längere Strecken in einem System bewegt, wird selbstinduzierte Verstärkung der Transmission näher betrachtet. Des weiteren werden von der Coulombwechselwirkung verursachte nichtlineare Effekte wie exzitoninduziertes Dephasieren in Volumenmaterial und verschränkte Zustände in Quantenpunkten untersucht, die einen Zusammenbruch der Hartree-Fock- Näherung darstellen. Zusammenfassend werden in dieser Arbeit verschiedene lineare und nichtlineare optische Effekte in Halbleiternanostrukturen verschiedener Dimensionalität mit Hilfe einer allgemeinen Theorie, die einen Dichtematrixansatz mit den Maxwellschen Gleichungen kombiniert, untersucht.}}, author = {{Förstner, Jens}}, keywords = {{tet_topic_qd, tet_topic_qw, tet_topic_phc}}, title = {{{Light Propagation and Many-Particle Effects in Semiconductor Nanostructures}}}, doi = {{10.14279/depositonce-999}}, year = {{2004}}, } @article{673, author = {{Waldmüller, I. and Förstner, Jens and Lee, S.-C. and Knorr, A. and Woerner, M. and Reimann, K. and Kaindl, R. A. and Elsaesser, T. and Hey, R. and Ploog, K. H.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, number = {{20}}, publisher = {{American Physical Society (APS)}}, title = {{{Optical dephasing of coherent intersubband transitions in a quasi-two-dimensional electron gas}}}, doi = {{10.1103/physrevb.69.205307}}, volume = {{69}}, year = {{2004}}, } @article{4272, abstract = {{The coupling of surface and bulk states at semiconductor surfaces through electron–phonon interaction is discussed. The governing equations are derived from a microscopic theory in the framework of the density matrix theory. To gain a first insight, model wave functions are used to simulate the dynamics of nonequilibrium electron distributions in three- and two-dimensional states, coupled by Fröhlich interaction. Typical time scales for the coupling are found to be in the order of few hundreds of femtoseconds.}}, author = {{Zeiser, Andreas and Bücking, Norbert and Götte, Jörg and Förstner, Jens and Hahn, Patrick and Schmidt, Wolf Gero and Knorr, Andreas}}, issn = {{0370-1972}}, journal = {{physica status solidi (b)}}, number = {{12}}, pages = {{R60--R62}}, publisher = {{Wiley}}, title = {{{Dynamics of the phonon-induced electron transfer between semiconductor bulk and surface states}}}, doi = {{10.1002/pssb.200409060}}, volume = {{241}}, year = {{2004}}, } @article{4288, abstract = {{We report the experimental observation and the theoretical modeling of self-induced-transparency signatures such as nonlinear transmission, pulse retardation and reshaping, for subpicosecond pulse propagation in a 2-mm-long InGaAs quantum-dot ridge waveguide in resonance with the excitonic ground-state transition at 10 K. The measurements were obtained by using a cross-correlation frequency-resolved optical gating technique which allows us to retrieve the field amplitude of the propagating pulses.}}, author = {{Schneider, S. and Borri, P. and Langbein, W. and Woggon, U. and Förstner, Jens and Knorr, A. and Sellin, R. L. and Ouyang, D. and Bimberg, D.}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, keywords = {{tet_topic_qd}}, number = {{18}}, pages = {{3668--3670}}, publisher = {{AIP Publishing}}, title = {{{Self-induced transparency in InGaAs quantum-dot waveguides}}}, doi = {{10.1063/1.1624492}}, volume = {{83}}, year = {{2003}}, } @article{4290, abstract = {{The nonlinear propagation of subpicosecond pulses resonant to the hh 1s exciton in Bragg-periodic multiple quantum wells is investigated experimentally and theoretically. We show coherent pulse breakup and its suppression for increasing pulse intensity in good agreement with calculations based on the semiconductor Maxwell-Bloch equations. For highly nonlinear excitation, pulse compression is observed which is strongly enhanced by the additional contribution of self-phase modulation in the barrier and substrate material.}}, author = {{Nielsen, N. C. and Kuhl, J. and Schaarschmidt, M. and Förstner, Jens and Knorr, A. and Koch, S. W. and Gibbs, H. M. and Khitrova, G. and Giessen, H.}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qw}}, number = {{5}}, pages = {{1484--1487}}, publisher = {{Wiley}}, title = {{{Pulse propagation in Bragg-resonant multiple quantum wells: from pulse breakup to compression}}}, doi = {{10.1002/pssc.200303207}}, year = {{2003}}, } @article{4292, abstract = {{We outline a theoretical description of the absorption linewidth of quantum well intersubband transitions by solving Maxwell’s equations for a non-local susceptibility including many particle effects. We show that the intersubband absorption results from a complex interplay between mean-field effects, dephasing contributions and light propagation effects, all being very sensitive to subband dispersion.}}, author = {{Waldmüller, Inès and Woerner, Michael and Förstner, Jens and Knorr, Andreas}}, issn = {{0370-1972}}, journal = {{physica status solidi (b)}}, keywords = {{tet_topic_qw}}, number = {{3}}, pages = {{474--477}}, publisher = {{Wiley}}, title = {{{Theory of the lineshape of quantum well intersubband transitions: optical dephasing and light propagation effects}}}, doi = {{10.1002/pssb.200303165}}, volume = {{238}}, year = {{2003}}, } @article{4294, abstract = {{The phonon-induced dephasing dynamics of semiconductor quantum dots during nonlinear optical excitation is studied using quantum kinetic equations. We find that despite the decoherence process Rabi oscillations occur even for relatively long pulse durations and that their signatures in pump-probe experiments only get suppressed for high input pulse areas.}}, author = {{Förstner, Jens and Weber, Carsten and Danckwerts, Juliane and Knorr, Andreas}}, issn = {{0370-1972}}, journal = {{physica status solidi (b)}}, keywords = {{tet_topic_qd}}, number = {{3}}, pages = {{419--422}}, publisher = {{Wiley}}, title = {{{Phonon-induced damping of Rabi oscillations in semiconductor quantum dots}}}, doi = {{10.1002/pssb.200303155}}, volume = {{238}}, year = {{2003}}, } @inproceedings{4296, abstract = {{A non-Markovian quantum kinetic theory of the coupled electron-phonon system in semiconductor quantum dots is used to analyze the nonlinear dipole decoherence and light propagation dynamics for arbitrary pulse strengths and lengths.}}, author = {{Förstner, Jens and Weber, C. and Danckwerts, J. and Knorr, A.}}, booktitle = {{Postconference Digest Quantum Electronics and Laser Science, 2003. QELS.}}, isbn = {{1557527490}}, keywords = {{tet_topic_qd}}, location = {{Baltimore, MD, USA, USA }}, publisher = {{IEEE}}, title = {{{Damping of electron density Rabi-oscillations and self-induced-transparency in semiconductor quantum dots}}}, doi = {{10.1109/qels.2003.238120}}, year = {{2003}}, } @inproceedings{4298, abstract = {{The linewidth of intersubband transitions resulting from simultaneous action of many-body contributions and radiative damping is analyzed. The processes are non-additive and a self-consistent treatment is necessary to explain recent experiments.}}, author = {{Waldmuller, I. and Förstner, Jens and Knorr, A. and Woerner, M. and Reimann, K. and Kaindl, R.A. and Hey, R. and Ploog, K.H.}}, booktitle = {{Postconference Digest Quantum Electronics and Laser Science, 2003. QELS.}}, isbn = {{1557527490}}, keywords = {{tet_topic_qw}}, location = {{ Baltimore, MD, (USA)}}, publisher = {{IEEE}}, title = {{{Correlated influence of carrier-carrier/carrier-phonon interaction and radiative damping on semiconductor intersubband transitions}}}, doi = {{10.1109/qels.2003.238217}}, year = {{2003}}, } @article{4322, abstract = {{We present the experimental observation and the theoretical modelling of self-induced transparency signatures such as nonlinear transmission, pulse retardation and reshaping for subpicosecond pulse propagation in a 2 mm-long InGaAs quantum-dot ridge waveguide at 10 K. The measurements were obtained using a cross-correlation frequency resolved optical gating technique which allows us to retrieve the field amplitude of the propagating pulses.}}, author = {{Schneider, S. and Borri, P. and Langbein, W. and Woggon, U. and Förstner, Jens and Knorr, A. and Sellin, R. L. and Ouyang, D. and Bimberg, D.}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qd}}, number = {{5}}, pages = {{1548--1551}}, publisher = {{Wiley}}, title = {{{Self-induced transparency in InGaAs quantum dot waveguides}}}, doi = {{10.1002/pssc.200303228}}, year = {{2003}}, } @article{671, author = {{Förstner, Jens and Weber, C. and Danckwerts, J. and Knorr, A.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_qd}}, number = {{12}}, pages = {{127401}}, publisher = {{American Physical Society (APS)}}, title = {{{Phonon-Assisted Damping of Rabi Oscillations in Semiconductor Quantum Dots}}}, doi = {{10.1103/physrevlett.91.127401}}, volume = {{91}}, year = {{2003}}, } @article{4300, abstract = {{The occurrence of non-Lorentzian lineshapes is analyzed for a variety of nanooptical semiconductor systems such as quantum wells and quantum dots. Their origin is traced back to light–matter interaction (light propagation) and many-particle correlations (electron–electron and electron– phonon interaction).}}, author = {{Förstner, Jens and Ahn, K.J. and Danckwerts, J. and Schaarschmidt, M. and Waldmüller, I. and Weber, C. and Knorr, A.}}, issn = {{0370-1972}}, journal = {{physica status solidi (b)}}, keywords = {{tet_topic_polariton}}, number = {{1}}, pages = {{155--165}}, publisher = {{Wiley}}, title = {{{Light Propagation- and Many-particle-induced Non-Lorentzian Lineshapes in Semiconductor Nanooptics}}}, doi = {{10.1002/1521-3951(200211)234:1<155::aid-pssb155>3.0.co;2-r}}, volume = {{234}}, year = {{2002}}, } @inproceedings{4305, abstract = {{On the basis of a density matrix approach including electron-electron scattering, a detailed analysis of the temporal dynamics and the dephasing process after optical excitation in intersubband emitters is presented for a wide range of parameters. }}, author = {{Waldmüller, Ines and Förstner, Jens and Knorr, Andreas}}, booktitle = {{Nonlinear Optics: Materials, Fundamentals and Applications}}, isbn = {{1557527210}}, keywords = {{tet_topic_qw}}, publisher = {{OSA}}, title = {{{Theory of ultrafast dynamics and lineshape of semiconductor quantum well intersubband emitters}}}, doi = {{10.1364/nlo.2002.we34}}, year = {{2002}}, } @article{4306, abstract = {{The coherent exciton-light coupling in pulse propagation experiments on the A-exciton resonance in bulk CdSe is investigated over a broad intensity range. At low light intensities, polariton propagation beats due to interference between excited states on both polariton branches are observed. In an intermediate intensity regime, the temporal polariton beating is suppressed in consequence of exciton-exciton interaction. At the highest light intensities, self-induced transmission and multiple pulse breakup are identified as a signature for carrier density Rabi flopping. Exciton-phonon scattering is shown to gradually eliminate coherent nonlinear propagation effects due to enhanced dephasing of the excitonic polarization. Calculations using the semiconductor Maxwell-Bloch equations are in qualitative agreement with the experimental data.}}, author = {{Nielsen, N. C. and Linden, S. and Kuhl, J. and Förstner, Jens and Knorr, A. and Koch, S. W. and Giessen, H.}}, issn = {{0163-1829}}, journal = {{Physical Review B}}, keywords = {{tet_topic_polariton}}, number = {{24}}, pages = {{245202--245202--10}}, publisher = {{American Physical Society (APS)}}, title = {{{Coherent nonlinear pulse propagation on a free-exciton resonance in a semiconductor}}}, doi = {{10.1103/physrevb.64.245202}}, volume = {{64}}, year = {{2002}}, } @article{4308, abstract = {{Features reminiscent of spectral hole burning in a homogeneous line are predicted to result from the interaction of small area pulses with the semiconductor exciton resonance. The small area pulses may be designed through pulse shaping or evolve naturally in bulk semiconductors via polaritonic effects. The spectral features exhibit signatures that are characteristic for the underlying material nonlinearity and should occur in any system with isolated spectral resonances and coherent nonlinearities.}}, author = {{Förstner, Jens and Knorr, A. and Koch, S. W.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_polariton}}, number = {{3}}, pages = {{476--479}}, publisher = {{American Physical Society (APS)}}, title = {{{Nonlinear Pulse Propagation in Semiconductors: Hole Burning within a Homogeneous Line}}}, doi = {{10.1103/physrevlett.86.476}}, volume = {{86}}, year = {{2002}}, } @article{4310, abstract = {{Nonlinear propagation of optical pulses through an extended bulk semiconductor is investigated using the coupled semiconductor Maxwell‐Bloch equations including excitation induced correlations. For short pulse excitation around the exciton resonance, the theory describes the development of polariton beats and their suppression at increasing input pulse intensities due to the coupling of single exciton states to the Coulomb‐correlated continuum of two‐exciton states. A comparison of the theoretical results with experimental observations for CdSe bulk material is presented.}}, author = {{Förstner, Jens and Knorr, A. and Kuckenburg, S. and Meier, T. and Koch, S.W. and Giessen, H. and Linden, S. and Kuhl, J.}}, issn = {{0370-1972}}, journal = {{physica status solidi (b)}}, keywords = {{tet_topic_polariton}}, number = {{1}}, pages = {{453--457}}, publisher = {{Wiley}}, title = {{{Nonlinear Polariton Pulse Propagation in Bulk Semiconductors}}}, doi = {{10.1002/1521-3951(200009)221:1<453::aid-pssb453>3.0.co;2-q}}, volume = {{221}}, year = {{2002}}, }