@article{63532, abstract = {{Room-temperature lasing is a key milestone in the development of miniaturized optoelectronic and photonic devices. We present a simple approach to synthesize phase-pure quasi-2D layered tin perovskite nanowires with varying quantum well thicknesses (n = 1 to 4). By incorporating a new organic spacer capable of forming a hydrogen-bonded organic framework, this method promoted anisotropic crystal growth and enhanced lattice rigidity. Furthermore, introducing molecular intercalants enabled controlled crystallization into well-defined nanowires that function as Fabry–Pérot cavities. Cavities made from n = 2 to 4 perovskites support efficient and robust near-infrared, room-temperature optically pumped lasing with the threshold as low as 75.8 μJ/cm2, cavity quality factor over 3000, and negligible degradation over 106 pulses. A cleaved coupled nanolaser was fabricated as a proof-of-concept device for photonic applications.}}, author = {{Kim, Jeong Hui and Simon, Jeffrey and Shao, Wenhao and Nian, Zhichen and Yang, Hanjun and Chen, Peigang and Triplett, Brandon and Li, Zhixu and Wu, Pengfei and Chen, Yuheng and Farheen, Henna and Pagadala, Karthik and Choi, Kyu Ri and Fruhling, Colton B. and Förstner, Jens and Boltasseva, Alexandra and Savoie, Brett M. and Shalaev, Vladimir M. and Dou, Letian}}, issn = {{0002-7863}}, journal = {{Journal of the American Chemical Society}}, keywords = {{tet_topic_opticalantenna}}, pages = {{jacs.5c14431}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Hydrogen-Bonded Organic Framework Enables Phase-Pure Layered Tin Perovskite Nanowires for Room-Temperature Lasing}}}, doi = {{10.1021/jacs.5c14431}}, year = {{2026}}, } @article{60891, abstract = {{Straight dielectric waveguide channels made from slabs of thin-film lithium niobate (TFLN), or lithium niobate on insulator (LNOI), are investigated in the linear regime, for channels of rib and strip type with common trapezoidal cross sections, in Z-cut and X-cut samples at varying on-chip orientation. We clarify the theoretical basis for the waveguides with potentially non-diagonal core permittivity. Symmetry classes can be distinguished that differ in their consequences for potential modal degeneracy and polarization conversion. Our rigorous numerical analysis by means of a finite-element solver takes the anisotropy of the lithium niobate cores rigorously into account. We discuss extensive data for effective indices, polarization properties, and hybridization of guided modes, in single- and multimode channels. Scans over the waveguide width and orientation as primary parameters are complemented by a series of illustrations of vectorial mode profiles. These turn out to be essentially complex in cases of X-cut channels at non-crystal-axis-aligned orientations.}}, author = {{Hammer, Manfred and Khan, Shahriar and Taheri, Behnood and Farheen, Henna and Förstner, Jens}}, issn = {{2770-0208}}, journal = {{Optics Continuum}}, keywords = {{tet_topic_waveguide}}, number = {{10}}, pages = {{2356}}, publisher = {{Optica Publishing Group}}, title = {{{TFLN channel waveguides of rib and strip type: Properties of guided modes}}}, doi = {{10.1364/optcon.569959}}, volume = {{4}}, year = {{2025}}, } @inproceedings{61760, abstract = {{We present a topology-optimized silicon nitride (Si3N4) coupler designed to enhance the coupling efficiency between integrated single-photon emitters and photonic waveguide modes. By leveraging inverse design techniques, we optimize the coupler’s geometry to maximize power transfer while maintaining fabrication feasibility by improving mode overlap and directional emission, addressing the challenge of low coupling efficiency caused by size mismatch and material incompatibility. Simulations demonstrate a substantial enhancement in photon extraction and waveguide coupling. This approach can be extended to other photonic devices, offering a versatile framework for improving quantum light-matter interactions in integrated photonics.}}, author = {{Farheen, Henna and Chen, Yuheng and Chen, Peigang and Kryvobok, Artem and Peana, Samuel and Senichev, Alexander and Shalaev, Vladimir M. and Boltasseva, Alexandra and Förstner, Jens and Kildishev, Alexander V.}}, booktitle = {{Photonic Computing: From Materials and Devices to Systems and Applications II}}, editor = {{Ni, Xingjie and Cai, Wenshan}}, keywords = {{tet_topic_waveguide}}, publisher = {{SPIE}}, title = {{{Topology-optimized silicon nitride coupler for integrated single-photon emitters}}}, doi = {{10.1117/12.3065734}}, year = {{2025}}, } @article{54668, abstract = {{Samples of dielectric optical waveguides of rib or strip type in thin-film lithium niobate (TFLN) technology are characterized with respect to their optical loss using the Fabry-Pérot method. Attributing the losses mainly to sidewall roughness, we employ a simple perturbational procedure, based on rigorously computed mode profiles of idealized channels, to estimate the attenuation for waveguides with different cross sections. A single fit parameter suffices for an adequate modelling of the effect of the waveguide geometry on the loss levels.}}, author = {{Hammer, Manfred and Babel, Silia and Farheen, Henna and Padberg, Laura and Scheytt, J. Christoph and Silberhorn, Christine and Förstner, Jens}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_waveguide}}, number = {{13}}, pages = {{22878}}, publisher = {{Optica Publishing Group}}, title = {{{Estimation of losses caused by sidewall roughness in thin-film lithium niobate rib and strip waveguides}}}, doi = {{10.1364/oe.521766}}, volume = {{32}}, year = {{2024}}, } @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{55751, abstract = {{Lateral leakage of TM modes in dielectric optical waveguides of rib/ridge or strip-loaded types can be fully suppressed, if the waveguide core is formed not through a strip that protrudes at one side (up) from the remaining lateral guiding slab, but through parallel strips on both sides (up and down), such that the resulting cross section becomes vertically symmetric. The fairly general arguments underlying the leakage suppression apply to TM modes of all orders simultaneously, and are independent of wavelength. These plus-shaped waveguides support strictly guided, non-leaky TM modes for, in principle, arbitrarily shallow etching.}}, author = {{Üstün, Necati and Farheen, Henna and Hammer, Manfred and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguide}}, number = {{9}}, pages = {{2077}}, publisher = {{Optica Publishing Group}}, title = {{{Symmetry-protected TM modes in rib-like, plus-shaped optical waveguides with shallow etching}}}, doi = {{10.1364/josab.528729}}, volume = {{41}}, year = {{2024}}, } @article{55989, abstract = {{Phased arrays are vital in communication systems and have received significant interest in the field of optoelectronics and photonics, enabling a wide range of applications such as LiDAR, holography, wireless communication, etc. In this work, we present a blazed grating antenna that is optimized to have upward radiation efficiency as high as 80% with a compact footprint of 3.5 μm × 2 μm at an operational wavelength of 1.55 μm. Our numerical investigations demonstrate that this antenna in a 64 × 64 phased array configuration is capable of producing desired far-field radiation patterns. Additionally, our antenna possesses a low side lobe level of -9.7 dB and a negligible reflection efficiency of under 1%, making it an attractive candidate for integrated optical phased arrays.}}, author = {{Farheen, Henna and Joshi, Suraj and Scheytt, J. Christoph and Myroshnychenko, Viktor and Förstner, Jens}}, issn = {{2515-7647}}, journal = {{Journal of Physics: Photonics}}, keywords = {{tet_topic_opticalantenna}}, pages = {{045010}}, publisher = {{IOP Publishing}}, title = {{{An efficient compact blazed grating antenna for optical phased arrays}}}, doi = {{10.1088/2515-7647/ad6ed4}}, volume = {{6}}, year = {{2024}}, } @article{56193, abstract = {{Dielectric slab waveguides made of thin-film-lithium-niobate (TFLN) media are consid-ered, for operation in the linear regime. We outline and implement a largely analytic procedure forrigorous modal analysis of three-layer slabs with birefringent, anisotropic core. For Z-cut wave-guides, the slab eigenmode problem separates into uncoupled sets of scalar equations for TE andTM modes. Slabs in X-cut configuration support mostly mildly hybrid eigenmodes, with clear pre-dominant TE or TM polarization, and with effective indices that depend on the propagation directionof the modes, relative to the crystal axes. Strong hybridization can be observed for near degeneratemodes in singular configurations without vertical symmetry, or in symmetric slabs where two nearlydegenerate modes are of the same symmetry class. Dispersion curves for slab thickness and propa-gation angle are discussed, for slabs with oxide and air cover. }}, author = {{Hammer, Manfred and Farheen, Henna and Förstner, Jens}}, issn = {{2770-0208}}, journal = {{Optics Continuum}}, keywords = {{tet_topic_waveguide}}, pages = {{532822}}, publisher = {{Optica Publishing Group}}, title = {{{Guided modes of thin-film lithium niobate slabs}}}, doi = {{10.1364/optcon.532822}}, year = {{2024}}, } @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}}, } @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}}, } @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}}, } @inproceedings{50466, abstract = {{A key challenge in designing efficient optical phased arrays is the lack of a well-designed radiator. This work explores horn antennas numerically optimized to target high upward radiation efficiency to be employed in silicon-based phased arrays capable of producing elegant radiation patterns in the far-field.}}, author = {{Farheen, Henna and Joshi, S. and Scheytt, J. Christoph and Myroshnychenko, Viktor and Förstner, Jens}}, booktitle = {{2023 IEEE Photonics Conference (IPC)}}, keywords = {{tet_topic_opticalantenna}}, publisher = {{IEEE}}, title = {{{Increasing the upward radiation efficiency of optical phased arrays using asymmetric silicon horn antennas}}}, doi = {{10.1109/ipc57732.2023.10360519}}, 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}}, } @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}}, } @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{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, Henna 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}}, }