TY - JOUR AB - 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. AU - Myroshnychenko, Viktor AU - Mulavarickal Jose, Pious Mathews AU - Farheen, Henna AU - Ejaz, Shafaq AU - Brosseau, Christian AU - Förstner, Jens ID - 52700 IS - 4 JF - Physica Scripta KW - tet_topic_ferro SN - 0031-8949 TI - From Swiss-cheese to discrete ferroelectric composites: assessing the ferroelectric butterfly shape in polarization loops VL - 99 ER - TY - JOUR AU - Alhaddad, Samer AU - Förstner, Jens AU - Grynko, Yevgen ID - 43018 JF - Journal of Quantitative Spectroscopy and Radiative Transfer KW - tet_topic_scattering SN - 0022-4073 TI - Numerical study of light backscattering from layers of absorbing irregular particles larger than the wavelength VL - 302 ER - TY - CONF AB - 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. AU - Farheen, Henna AU - Yan, Lok-Yee AU - Leuteritz, Till AU - Qiao, Siqi AU - Spreyer, Florian AU - Schlickriede, Christian AU - Quiring, Viktor AU - Eigner, Christof AU - Silberhorn, Christine AU - Zentgraf, Thomas AU - Linden, Stefan AU - Myroshnychenko, Viktor AU - Förstner, Jens ED - García-Blanco, Sonia M. ED - Cheben, Pavel ID - 43051 KW - tet_topic_opticalantenna T2 - Integrated Optics: Devices, Materials, and Technologies XXVII TI - Tailoring the directive nature of optical waveguide antennas ER - TY - CONF AB - 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. AU - Farheen, Henna AU - Strauch, Andreas AU - Scheytt, J. Christoph AU - Myroshnychenko, Viktor AU - Förstner, Jens ED - García-Blanco, Sonia M. ED - Cheben, Pavel ID - 43052 KW - tet_topic_opticalantenna T2 - Integrated Optics: Devices, Materials, and Technologies XXVII TI - Optimized silicon antennas for optical phased arrays ER - TY - JOUR AB - 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. AU - Hammer, Manfred AU - Farheen, Henna AU - Förstner, Jens ID - 43245 IS - 4 JF - Journal of the Optical Society of America B KW - tet_topic_waveguide SN - 0740-3224 TI - How to suppress radiative losses in high-contrast integrated Bragg gratings VL - 40 ER - TY - JOUR AB - 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. AU - Hähnel, David AU - Golla, Christian AU - Albert, Maximilian AU - Zentgraf, Thomas AU - Myroshnychenko, Viktor AU - Förstner, Jens AU - Meier, Cedrik ID - 44097 IS - 1 JF - Light: Science & Applications KW - tet_topic_meta SN - 2047-7538 TI - A multi-mode super-fano mechanism for enhanced third harmonic generation in silicon metasurfaces VL - 12 ER - TY - JOUR AB - 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. AU - Hähnel, David AU - Förstner, Jens AU - Myroshnychenko, Viktor ID - 45596 JF - ACS Photonics KW - tet_topic_meta SN - 2330-4022 TI - Efficient Modeling and Tailoring of Nonlinear Wavefronts in Dielectric Metasurfaces ER - TY - JOUR AB - 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. AU - Farheen, Henna AU - Strauch, Andreas AU - Scheytt, J. Christoph AU - Myroshnychenko, Viktor AU - Förstner, Jens ID - 50012 JF - Photonics and Nanostructures - Fundamentals and Applications KW - tet_topic_opticalantenna SN - 1569-4410 TI - Optimized, Highly Efficient Silicon Antennas for Optical Phased Arrays VL - 58 ER - TY - CONF AB - 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. AU - Lange, Sven AU - Hilleringmann, Ulrich AU - Hedayat, Christian AU - Kuhn, Harald AU - Förstner, Jens ID - 49890 KW - Planar coils KW - inductive locating KW - magnetic fields KW - environmental influences KW - eddy currents KW - tet_topic_hf T2 - 2023 IEEE Conference on Antenna Measurements and Applications (CAMA) TI - Characterization of Various Environmental Influences on the Inductive Localization ER - TY - JOUR AB - 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. AU - Bauch, David AU - Siebert, Dustin AU - Jöns, Klaus AU - Förstner, Jens AU - Schumacher, Stefan ID - 48599 JF - Advanced Quantum Technologies KW - tet_topic_qd SN - 2511-9044 TI - On‐Demand Indistinguishable and Entangled Photons Using Tailored Cavity Designs ER -