arXiv subjects

Hamza Kurt

Publications and source records attributed to Hamza Kurt.

At least 19 recordsLinked to original sources

arXiv2025

Electronic-Photonic Interface for Multiuser Optical Wireless Communication

We demonstrate an electronic-photonic (EP) interface for multiuser optical wireless communication (OWC), consisting of a multibeam optical phased array (MBOPA) along with co-integrated electro-optic (EO) modulators and high-speed CMOS drivers. The MBOPA leverages a path-length difference in the optical phased array (OPA) along with wavelength-division multiplexing technology for spatial carrier aggregation and multiplexing. To generate two and four pulsed amplitude modulation signals, and transmit them to multiple users, we employ an optical digital-to-analog converter technique by using two traveling-wave electrode Mach-Zehnder modulators, which are monolithically integrated with high-speed, wide-output-swing CMOS drivers. The MBOPA and monolithic EO modulator are implemented by silica wafer through planar lightwave circuit fabrication process and a 45-nm monolithic silicon photonics technology, respectively. We measured and analyzed two-channel parallel communication at a data rate of 54 Gbps per user over the wireless distance of 1 m. To the best of our knowledge, this is the first system level demonstration of the multi-user OWC using the in-house-designed photonic and monolithically integrated chips. Finally, we suggest best modulation format for different data rate and the number of multibeams, considering effects of the proposed OPA and the monolithic modulator.

physics.optics↗

arXiv2024

Ultra-miniaturized Bloch mode metasplitters for one-dimensional grating waveguides

We present, for the first time, power splitters with multiple channel configurations in one-dimensional grating waveguides (1DGWs) that maintain crystal lattice-sensitive Bloch mode profiles without perturbation across all output channels, all within an ultra-miniaturized footprint of just 2.1 x 2.2 {\mu}m^2. This novel capability reduces the need for transition regions, simplifies multi-channel configurations of 1DGWs, and maximizes the effective use of chip area. The pixelated metamaterial approach, integrated with a time-domain heuristic algorithm, is utilized to concurrently achieve broadband operation, optimized dispersion control, and minimal loss. We experimentally demonstrate that our 1x2 and 1x3 metasplitters achieve average minimum losses per channel of 3.80 dB and 5.36 dB, respectively, just 0.80 dB and 0.59 dB above ideal splitting. The measurements for both designs demonstrate a 1 dB bandwidth of 15 nm, with excellent uniformity across all output channels. These versatile metasplitter designs can serve as fundamental building blocks for ultrahigh-bandwidth, densely integrated photonic circuits and in scenarios where slow light is essential.

physics.optics↗

arXiv2024

Ultrafast pulse propagation time-domain dynamics in dispersive one-dimensional photonic waveguides

Ultrafast pulses, particularly those with durations under 100 femtoseconds, are crucial in achieving unprecedented precision and control in light-matter interactions. However, conventional on-chip photonic platforms are not inherently designed for ultrafast time-domain operations, posing a significant challenge in achieving essential parameters such as high peak power and high temporal resolution. This challenge is particularly pronounced when propagating through dispersive integrated waveguides, unlike classical applications where dispersion is typically near-zero or linear. In addressing this challenge, we present a design methodology for ultrafast pulse propagation in dispersive integrated waveguides, specifically focused on enhancing the time-domain characteristics of one-dimensional grating waveguides (1DGWs). The proposed methodology aims to determine the optimal structural parameters for achieving maximum peak power, enhanced temporal resolution, and extended pulse storage duration during ultrafast pulse propagation. To validate this approach, we design and fabricate two specialized 1DGWs on a silicon-on-insulator (SOI) platform. A digital finite impulse response (FIR) model, trained with both transmission and phase measurement data, is employed to obtain ultrafast time-domain characteristics, enabling easy extraction of these results. Our approach achieves a 2.78-fold increase in peak power and reduces pulse broadening by 24%, resulting in a smaller sacrifice in temporal resolution. These results can possibly pave the way for advanced light-matter interactions within dispersive integrated waveguides.

physics.optics↗

arXiv2022

Curved beam generation and its experimental realization by rectangular prism with asymmetric polynomial back surface

With the discovery of self-accelerating beams, possibility of obtaining curved light beams in free space has been realized. These special beams paved the way for many new applications as well as the exploration of novel beam types. Recently, great research effort has been conducted to realize different types of curved beams such as photonic hook and airy beam. These curved types of beams are obtained by introducing structural asymmetry or applying non-uniform dielectric distribution to the input and output face of the structure. With this regard, we propose specially designed asymmetric structure with polynomial back surface which generates curved light beams. Proposed lossless dielectric structure can generate curved beams at frequencies varying from 15.78 GHz to 20.09 GHz and corresponding curvature angles of minimum 41.34 and maximum 57.58 degrees, respectively. The physical background of the curved beam formation is based on interference of the exiting light waves that diffract on upper and bottom polynomial surfaces which provides phase modulation leading to the curved trajectory of the propagating light. In addition, the observed beam steering effect is further investigated and the experimental verification in microwave region is conducted to verify our design's operation principle.

physics.class-ph↗

arXiv2022

Reinforcement learning enabled the design of compact and efficient integrated photonic devices

In this paper, we introduce the design approach of integrated photonic devices by employing reinforcement learning known as attractor selection. Here, we combined three-dimensional finite-difference time-domain method with attractor selection algorithm, which is based on artificial neural networks, to achieve ultra-compact and highly efficient photonic devices with low crosstalk such as wavelength demultiplexers and a polarization splitter. The presented devices consist of silicon-on-insulator materials, which are compatible with complementary metal-oxide-semiconductor technology, and their structural dimensions enable the possible fabrication process in the future. The numerical results are presented for the near-infrared wavelengths at around 1550 nm, and the performance of designed photonic devices with footprint of 3x3 um2 are compared with the previously reported structures. Consequently, the reinforcement learning is successfully applied to design smaller and superior integrated photonic devices where the use of presented approach can be further expanded to different applications.

physics.app-ph↗

arXiv2022

Multi-directional cloak design by all dielectric unit-cell optimized structure

In this manuscript, we demonstrate the design and experimental proof of an optical cloaking structure which multi-directionally conceals a perfectly electric conductor (PEC) object from an incident plane wave. The dielectric modulation around the highly reflective scattering PEC object is determined by an optimization process for multi-directional cloaking purposes. And to obtain the multi-directional effect of the cloaking structure, an optimized slice is mirror symmetrized through a radial perimeter. Three-dimensional (3D) finite-difference time-domain method is integrated with genetic optimization to achieve cloaking design. In order to overcome the technological problems of the corresponding devices in the optical range and to experimentally demonstrate the proposed concept, our experiments were carried out on a scale model in the microwave range. The scaled proof-of-concept of proposed structure is fabricated by 3D printing of polylactide material, and the brass metallic alloy is used as a perfect electrical conductor for microwave experiments. A good agreement between numerical and experimental results is achieved. The proposed design approach is not restricted only to multi-directional optical cloaking but can also be applied for different cloaking scenarios dealing with electromagnetic waves in nanoscales as well as other types of such as acoustic waves. Using nanotechnology, our scale proof-of-concept research will take the next step towards the creation of "optical cloaking" devices.

physics.app-ph↗

arXiv2021

Ultra-compact, high-NA achromatic multilevel diffractive lens via metaheuristic approach

Recently, the multilevel diffractive lenses (MDLs) have attracted considerable attention mainly due to their superior wave focusing performance; however, efforts to correct the chromatic aberration are still in progress. Here, we demonstrate the numerical design and experimental demonstration of high-numerical aperture (NA) (${\sim}0.99$), diffraction-limited achromatic multilevel diffractive lens (AMDL) operating in microwave range $10 GHz$ - $14 GHz$. A multi-objective differential evolution (MO-DE) algorithm is incorporated with the three-dimensional finite-difference time-domain (3D FDTD) method to optimize both the heights and widths of each concentric ring (zone) of the AMDL structure. In this study, the desired focal distance $ΔF_d$ is treated as an optimization parameter in addition to the structural parameters of the zones for the first time. In other words, MO-DE diminishes the necessity of predetermined focal distance and center wavelength by also providing an alternative method for phase profile tailoring. The proposed AMDL can be considered as an ultra-compact, the radius is $3.7{λ_c}$ where ${λ_c}$ is the center wavelength (i.e., $12 GHz$ frequency), and flat lens which has a thickness of ${λ_c}$. The numerically calculated full-width at half-maximum (FWHM) values are below $0.554λ$ and focusing efficiency values are varying between $28{\%}$ and $45.5{\%}$. To experimentally demonstrate the functionality of the optimized lens, the AMDL composing of polylactic acid material (PLA) polymer is fabricated via 3D-printing technology. The numerical and experimental results are compared, discussed in detail and a good agreement between them is observed. Moreover, the verified AMDL in microwave regime is scaled down to the visible wavelengths to observe achromatic and diffraction-limited focusing behavior between $380 nm$ - $620 nm$ wavelengths.

physics.optics↗

arXiv2020

Nanostructured Multilayer Coatings for Spatial Filtering

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far-field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in micro-resonators to access the far-field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, we propose and demonstrate a conceptually novel mechanism of spatial filtering in the near-field domain, by a nanostructured multilayer coating - a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse direction to the beam propagation. The structure is built on a nano-modulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self-repeating modulation in the longitudinal direction. We experimentally demonstrate a 5 micron thick photonic multilayer structure composed of nanostructured multiple layers of alternating high- and low-index materials providing spatial filtering in the near-infrared frequencies with 2° low angle passband. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers.

physics.optics↗

arXiv2020

Inverse design of compact optical cloaks and experimental demonstration at microwave frequencies

Inverse design in photonics has gathered increasing attention as a powerful approach that goes beyond the intuition-based designs. In this Letter, we present the inverse design and experimental demonstration of compact optical cloaks at microwave frequencies is conducted. Two different configurations of rectangular and circular cloaks are numerically designed to reduce the scatterings of incident light interacting with a perfect electrical conductor object. The designed cloaking structures consist of dielectric polylactide material with a low refractive index and they are fabricated by 3D printing approach. The experimental measurements are in good agreement with the numerical calculations. The designed region covering (4λ x 4λ) area enables hiding circular object of λ diameter where λ denotes the wavelength of incident light. The proposed approach may enable the concealment of different objects possessing various size and shapes.

physics.app-ph↗

arXiv2020

Intensity tuning of the edge states in the imperfect topological waveguides based on the photonic crystals with the C3 point group symmetry

In this paper, we explore the topological behavior of a two-dimensional honeycomb photonic crystal (PC) based on the presence of double Dirac-cone connected the orbitals p and d, due to the C6 point group symmetry of the hexagonal PCs. Removing the four-fold degeneracies between the bands at the Dirac point can be achieved by introducing three small dielectric rods near the bigger ones to realize the perturbed PCs with the C3 point group symmetry with different topological features. By proposing the unique structure involving two PCs with different topological effects, one may study the one-way light distribution along the local boundary in spite of the defects, cavities, and disorders. Moreover, we investigate the variation of the transmitted intensity values under different defect conditions and realize that the size, location and material type affect the transmitted light. In the other words, tunable intensity of the edge states can be achieved through adjusting the defects such that by increasing the radius of rods, the intensity of the edge states can be enhanced or by increasing their distance from the unit cell center, the intensity will be decreased. For example, by increasing the radius of one of the rods, the intensity of the edge states is increased up to the 130%. Additionally, by moving the position of the mentioned rod along the direction, x, the intensity of the edge states will be decreased to 82.08%. Finally, topological rhombic resonator enables unidirectional filtering of guided mode. The fact that different light manipulation scenarios can be realized provides a unique aspect for topological photonic insulators.

physics.app-ph↗

arXiv2019

Crossed chiral band approximation for wideband self-collimation of light

We propose a perspective to the evaluation of the wide bandwidth phenomenon, by introducing the band tailoring and chiral band approximation on the self-collimation effect for low-symmetric photonic structures. In the case of the crossing of the bands, we claim the excitation of the lower mode can provide the utilization of the entire bandwidth by suppressing the intersection regions where the frequencies tend to mix. Thereby, we design broadband self-collimation capable, defect-free photonic structures and examine their performances. A fractional bandwidth of $0.35$ (${a}\backslashλ=0.429-0.607$) and $0.37$ (${a}\backslashλ=0.481-0.701$) are achieved for radii of ${r}=0.25{a}$ and ${r}=0.23{a}$, respectively. We explore the full-range collimation using transmission and E-field intensity analysis in addition to band diagrams and group velocity dispersions. Moreover, we indicate all-angle collimation validity even for highly tilted sources up to an angle of $80^\circ$.

physics.app-ph↗

arXiv2019

Analytical, numerical and experimental investigation of Luneburg lens system for directional cloaking

In this study, the design of a directional cloaking based on the Luneburg lens system is proposed and its operating principle is experimentally verified. The cloaking concept is analytically investigated via geometrical optics and numerically realized with the help of the finite-difference time-domain method. In order to benefit from its unique focusing and/or collimating characteristics of light, the Luneburg lens is used. We show that by the proper combination of Luneburg lenses in an array form, incident light bypasses the region between junctions of the lenses, i.e., the "dark zone." Hence, direct interaction of an object with propagating light is prevented if one places the object to be cloaked inside that dark zone. This effect is used for hiding an object which is made of a perfectly electric conductor material. In order to design an implementable cloaking device, the Luneburg lens is discretized into a photonic crystal structure having gradually varying air cylindrical holes in a dielectric material by using Maxwell Garnett effective medium approximations. Experimental verifications of the designed cloaking structure are performed at microwave frequencies of around 8 GHz. The proposed structure is fabricated by three-dimensional printing of dielectric polylactide material and a brass metallic alloy is utilized in place of the perfectly electric conductor material in microwave experiments. Good agreement between numerical and experimental results is found.

physics.app-ph↗

arXiv2019

Inverse Design of All-dielectric Parallel-Plane Mirror Resonator

In this study, we used parallel plane mirror resonator analogy to design all-dielectric optical resonator that is performed with the objective-first inverse design algorithm. Confinement of the light is succeeded via predefined objective function to create symmetric mirror regions for the fundamental transverse-electric polarization mode. The algorithm creates bandgap in random structure to obtain resonance peak at the desired wavelength without any intuitive scanning of the parameter space. The first order mode is confined on the cavity region at pre-defined wavelength. The obtained structure is analysed by using the two-dimensional finite-difference time-domain method. The proposed structure has a compact configuration with a footprint of $13.394 \times 0.592 μm^2$.

physics.optics↗

arXiv2019

High-performance 2D 1xN T-junction Wavelength (De)Multiplexer Systems by Inverse Design

Previously proposed designs of integrated photonic devices have used the intuitive brute force approach or optimization methods that employ parameter search algorithms. However, a small parameter space and poor exploitation of the underlying physics have limited device performance, functionality, and footprint. In this paper, we propose efficient and compact 2D 1xN in-plane-incidence wavelength demultiplexers by using recently developed objective-first inverse design algorithm. Output ports in the presented 1xN photonic devices are located along the transverse to the input channel. Ultra-high device performance was achieved for the specific designs of 1x2, 1x4, and 1x6 wavelength (de)multiplexers with small footprints 2.80 um x 2.80 um, 2.80 um x 4.60 um, 2.80 um x 6.95 um, respectively. We used two approaches to binarization-level-set and binarization-cost-to obtain silicon wavelength demultiplexer considering fabrication constraints. For instance, the transmission efficiency of binarization-cost 1x2 demultiplexer was -0.30 dB for 1.31 um and -0.54 dB at 1.55 um while crosstalk at the operating wavelengths are negligibly small, i.e., -17.80 and -15.29 dB, respectively. Moreover, for the binarization-cost 1x4 demultiplexer, the transmission efficiency values were approximately -1.90 dB at 1.31, 1.39, 1.47, and 1.55 um as the crosstalk was approximately -13 dB. Furthermore, the objective-first algorithm was used to employ our demultiplexers as multiplexers which means the ports that were once used as inputs in demultiplexers are designed to be used as outputs. The inverse design approach that allows for the implementation of more than six output channels together with the proposed functionalities can help develop compact and manufacturable 2D 1xN couplers.

physics.app-ph↗

arXiv2019

Active beam steering and afocal zooming by nematic liquid crystal infiltrated graded index photonic structures

This study presents active beam steering and afocal zooming of light by incorporating liquid crystals (LCs) with graded index photonic crystal (GRIN PC). The GRIN PC structures are composed of low refractive index polymer annular rods having gradually varied radii of holes. To actively manipulate incident light, the annular rods are infiltrated with nematic LCs. By applying an external voltage to the infiltrated LCs, the effective index profile of the low-index GRIN PC structure is modulated without introducing any mechanical movement. The incident beam deflection and corresponding focal distance modulation are tuned only by controlling the applied bias voltage. In the present work, hyperbolic secant refractive index profile is chosen to design GRIN PC structures. To design GRIN PC structure with annular PCs, Maxwell-Garnett effective medium approximation is employed. Moreover, we analytically express the relation between infiltrated LCs and gradient parameter to show the physical background of the tuning ability of the proposed devices. Also, beam steering and afocal zooming devices are analytically investigated via geometrical optics and numerically realized with the help of the finite-difference time-domain method. A beam deflection with an angle change of Δθout= 44° and a light magnification with maximum x2.15 are obtained. LCs are inexpensive materials and work under low voltage/power condition. This feature can be used for designing an electro-optic GRIN PC device that can be useful in various optical applications.

physics.app-ph↗

arXiv2019

Reduced Symmetric 2D Photonic Crystal Cavity with Wavelength Tunability

In this paper, we propose a microcavity supported by a designed photonic crystal structure (PhC) that supplies both tunability of cavity modes and quality factor of cavity. Low symmetric defect region provides a trigger effect for the frequency shifting by means of rotational manipulation of small symmetry elements. Deviation of effective filling ratio as a result of rotational modification within the defect region results in the emanation of cavity modes at different frequencies. Here, we numerically demonstrate the frequency shifting for each obtained mode with respect to defect region architecture. In addition to wavelength tunability, quality factor, mode volume, and Purcell factors are analyzed for the slightly modified structures. Also, electric field distributions of each mode that emerge at distinct frequencies have been also studied at adjusted frequency modes which are observed for all rotational modification scenarios as $θ_{rot} =[0^\circ,15^\circ,30^\circ, 40^\circ] $. After the investigations in 2D of silicon material ($ε_r=12$), 3D simulations are performed and the collected data is used for the stacking approximation of 3D structures to get the 2D, thus the cross-checking of the quality factor that acquired from the 2D simulation can be executed by comparison with 3D. Limited 3D results are projected to approximate 2D ones step by step and get an exponential trend which reaches in the limit to the $10^8$ value for Q-factor. Besides, 2D and 3D simulations of alumina ($ε_r=9.61$) in terms of mode analysis and quality factor have been repeated considering the microwave experiments. Therefore, experimental analysis is compared with the numerical results and good agreement between the two is found.

physics.app-ph↗

arXiv2018

Broadband polarization-independent low-crosstalk metasurface lens array-based mid wave infrared focal plane arrays

The miniaturization of pixel is essential for achieving high-resolution, planar, compact-size focal plane arrays (FPAs); however, the resulted increase in the optical crosstalk between adjacent pixels leads to serious drawback and trade-off. In the current work, we design and propose an efficient broadband polarization-insensitive all-dielectric metasurface lens array-based focal plane arrays (FPA) operating in the mid-wave infrared (MWIR). High focusing efficiency over 0.85 with superior optical crosstalk performance is achieved. We demonstrated that optical crosstalk can be reduced to low levels below 2.8% with high efficiency. For the device performance, a similar figure-of-merit (FoM) from the previous reports was used and our device achieved FoM of 91 which outperformed all other types MWIR FPAs designed so far. Proposed metasurface lens arrays demonstrate great potential for increasing the signal to noise ratio and sensitivity thus paving the way for compact-size, high-resolution FPAs.

physics.optics↗

arXiv2017

Invisibility on demand based on a generalized Hilbert transform

Designing invisible objects without the usage of extreme materials is a long-sought goal for photonic applications. Invisibility techniques demonstrated so far typically require high anisotropy, gain and losses, while also not being flexible. Here we propose an invisibility approach to suppress the scattering of waves from/to given directions and for particular frequency ranges, i.e. invisibility on demand. We derive a Born approximation-based generalized Hilbert transform for a specific invisibility arrangement relating the two quadratures of the complex permittivity of an object. The theoretical proposal is confirmed by numerical calculations, indicating that near-perfect invisibility can be attained for arbitrary objects with low-index contrast. We further demonstrate the cases where the idea can be extended to high-index objects or restricted to within practical limits by avoiding gain areas. The proposed concept opens a new route for the practical implementation of complex-shaped objects with arbitrarily suppressed scatterings determined on demand.

physics.optics↗