arXiv subjects

Mirbek Turduev

Publications and source records attributed to Mirbek Turduev.

14 recordsLinked to original sources

arXiv2025

Geometric Optimization and IPA-Induced Dispersion Tuning in Solid-Core Photonic Crystal Fibers

This study presents a numerical investigation of solid-core photonic crystal fibers with circular and hexagonal cladding geometries. The goal is to optimize optical parameters for nonlinear photonics and environmental sensing. Full-vectorial simulations using FDTD, PWE, and FDE are used to analyze the effects of core diameter, pitch, and air filling fraction on the zero-dispersion wavelength, nonlinear coefficient, effective mode area, and confinement loss. Reducing the core diameter from 2.4 to 1.4 microns tunes the zero-dispersion wavelength from 791 to 646 nanometers and increases the nonlinear coefficient by 72 percent, from 72 to 124 inverse watts per kilometer. The study also examines the effect of isopropyl alcohol infiltration, which causes a red-shift in dispersion and degrades confinement. These results offer a design framework that balances nonlinear efficiency and environmental robustness for supercontinuum generation and chemical sensing.

physics.optics↗

arXiv2024

Enhanced self-collimation effect by low rotational symmetry in hexagonal lattice photonic crystals

In this study, we present the design of a photonic crystal (PC) structure with a hexagonal lattice, where adjustments to the PC unit cell symmetry reveal an all-angle self-collimation (SC) effect. By optimizing opto-geometric parameters, such as the rotational angle of auxiliary rods and adjacent distances, we analyze the SC property in detail, leveraging group velocity dispersion (GVD) and third-order dispersion (TOD) characteristics. We also investigate the relationship between symmetry properties and their influence on dispersion characteristics. Through symmetry manipulation, we gain a comprehensive understanding of the underlying mechanisms governing light collimation and confinement in the proposed configurations. The PC structure with a $C_1$ symmetry group exhibits all-angle SC effect within the range of $a/λ=0.652$ and $a/λ=0.668$ normalized frequencies, with a bandwidth of $Δω/ω_c = 2.4\%$. Further breaking the symmetry, transforming from $C_1$ to $C_2$ group symmetry, enhances the SC bandwidth to $Δω/ω_c = 6.5\%$ and reveals the perfect linear equi-frequency contours (EFC) at two different frequency bands: all-angle SC between $a/λ=0.616$ and $a/λ=0.656$ normalized frequencies in the \nth{4} transverse magnetic (TM) band and between $a/λ=0.712$ and $a/λ=0.760$ in the \nth{5} TM band. Additionally, we propose a composite/hybrid PC structure resembling $C_2$ group symmetry, where two auxiliary rods are replaced by rectangular photonic wires with the same refractive index and width equal to the diameter of auxiliary rods. This hybrid structure exhibits an all-angle SC effect with an operating bandwidth of $Δω/ω_c = 11.7\%$, displays near-zero GVD and TOD performance, and offers enhanced robustness against potential fabrication precision issues.

physics.optics↗

arXiv2023

The Effect of Symmetry Breaking in Coupled Cavity Photonic Crystal Waveguide on Dispersion Characteristics

In this study, we explore the effect of integrated auxiliary rods at varying angles to the primary cavity rod on the dispersion characteristics of the photonic crystal coupled cavity waveguide (PC CCW). Here, it is intended to break the symmetry of the cavity region by introducing auxiliary rods which gives the degree of freedom for tuning effective index of the PC waveguide. Furthermore, rotational angle variations of auxiliary rods reveal slow light operation of the PC CCW where the group index is maximized and group velocity dispersion, as well as the third-order dispersion, are minimized. In addition, auxiliary rods with a broken symmetry increase not only group index but also operating bandwidth and accordingly increase group bandwidth product by 675\%. Leveraging these results, we demonstrate effective rainbow trapping by manipulating the auxiliary rod angles in photonic crystal coupled cavity waveguides. Our results have encouraging implications for optical buffering, multiplexing, demultiplexing, advanced time-domain and spatial signal processing.

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↗

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

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↗

arXiv2017

Machine learning based compact photonic structure design for strong light confinement

We present a novel approach based on machine learning for designing photonic structures. In particular, we focus on strong light confinement that allows the design of an efficient free-space-to-waveguide coupler which is made of Si- slab overlying on the top of silica substrate. The learning algorithm is implemented using bitwise square Si- cells and the whole optimized device has a footprint of $\boldsymbol{2 \, μm \times 1\, μm}$, which is the smallest size ever achieved numerically. To find the effect of Si- slab thickness on the sub-wavelength focusing and strong coupling characteristics of optimized photonic structure, we carried out three-dimensional time-domain numerical calculations. Corresponding optimum values of full width at half maximum and coupling efficiency were calculated as $\boldsymbol{0.158 λ}$ and $\boldsymbol{-1.87\,dB}$ with slab thickness of $\boldsymbol{280nm}$. Compared to the conventional counterparts, the optimized lens and coupler designs are easy-to-fabricate via optical lithography techniques, quite compact, and can operate at telecommunication wavelengths. The outcomes of the presented study show that machine learning can be beneficial for efficient photonic designs in various potential applications such as polarization-division, beam manipulation and optical interconnects.

physics.optics↗

arXiv2016

Photonic Crystals Engineering For Light Manipulation: Low Symmetry, Graded Index and Parity Time Symmetry

The great interest to the two and three dimensionally periodic structures, called photonic crystals (PCs), has begun with the pioneer works of Yablonovitch and John as one can efficiently control the propagation of the electromagnetic (EM) waves in the same manner with semiconductors that affect the electron conduction. One of the main peculiar properties of PCs is that they have photonic band gap in the transmission spectrum similar to electronic band gap and hence, they are able to prevent the light to propagate in certain frequency regions irrespective of the propagation direction in space. Inside the band gaps, neither optical modes nor spontaneous emissions exist. Breaking the rotational and mirror symmetries of PC unit cells provides rich dispersive features such as tilted self-collimation, and wavelength de-multiplexing effects. Another important issue in PC designs is that it is feasible to design graded index medium if the parameters of the two dimensional PCs is intentionally rearranged. That type of configuration is known as Graded index photonic crystals (GRIN PCs). The implementations of GRIN via periodic structures provide great flexibilities in terms of designing different index gradient and photonic integrated circuit components such as couplers, lenses, and mode order converters. It is crucial to deliver optical signal without any loss for the long distances where light diffraction plays an important role. Hence, dealing with the alternative solution to light diffraction phenomena using 2D axicon shape annular type photonic structure is another topic of this thesis. In addition to conventional photonic all dielectric structures, we have proposed gain-loss modulated parity-time (PT-) symmetric photonic structures to obtain strong asymmetric light transmission close to the crystallographic resonances or, equivalently, close to high-symmetry points.

physics.optics↗