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In this study, a two-dimensional low-symmetric photonic crystal (PC) configuration with elliptical geometry is presented and its slow-light (SL) effect is investigated. Reducing the symmetry in the PC unit cell provides slow modes at the higher transverse electric bands. The calculated group index and the corresponding normalized bandwidth equal to {ng, BW}={63.56, 0.0065}. That corresponds to a value of figure of merit (FOM)=0.4344 defined by the product of the average group index and the normalized bandwidth, FOM=〈ng〉BW, which is comparable to the values available in literature. Tracing the whole edges of the Brillouin zone, strongly excited SL modes are observed only along Γ-X but not along Γ-X’ or Γ-M. That condition allows for the design of low-symmetric PC waveguides with finite thicknesses at the expense of lowering group index value. The SL effect is still obtained for the proposed low-symmetric PCs having finite thicknesses, which is numerically proved via finite-difference time-domain methods. It is important to note that non-dispersive SL Bloch modes exist through the non-zero k-vector components of Brillouin zone. Hence, such a defect-free (without either point- or line- defect) SL PC design may have a great potential for the use of compact photonic devices such as in optical switching and biochemical sensing applications.

Optical sensing devices has a great potential in both industrial and biomedical applications for the detection of biochemicals, toxic substances or hazardous gases thanks to their sustainability and high-selectivity characteristics. Among different kinds of optical sensors based on such as fibers, surface plasmons and resonators; photonic crystal (PC) based optical sensors enable the realization of more compact and highly efficient on-chip sensing platforms due to their intriguing dispersive relations. Interferometric devices based on PCs render possible the creation of biochemical sensors with high sensitivity since a slight change of sensor path length caused by the captured biochemicals could be detected at the output of the interferometer via the interferences of separated beams. In this study, a new type of Mach-Zehnder Interferometer (MZI) using low-symmetric Si PCs is proposed, which is compatible with available CMOS technology. Intended optical path difference between the two MZI channels is provided by the periodic alignments of symmetry-reduced PC unit cells in the MZI arms. Unlike the conventional symmetrical PC based MZIs, Fano resonances exist for the proposed MZI design, i.e. transmission dips and peaks appear in the output spectrum, and the location of dip and peak frequencies in transmission spectra can be efficiently controlled by utilizing interference phenomenon. Exploiting this effect, any refractive index change at the surrounding medium could be distinctly observed at the transmission spectra. In the view of such results, it is convenient to say that the proposed MZI configuration is suitable for efficient optical sensing of toxic gases as well as liquids. The designed all-dielectric MZI system is numerically investigated in both spectral and spatial domains to analyze its interferometric tunability: an optical sensitivity of about 300 nm/RIU is calculated for gaseous analytes whereas that sensitivity value is around 263.2 nm/RIU in the case of liquid analytes. Furthermore, high quality factor of Q > 45000 is obtained at Fano resonances with Figure-of-Merit (FoM) value of FoM ∼ 8950 RIU−1(7690 RIU−1) in the case of gas analytes (liquid analytes), which is the indication of enhanced optical sensing performance of the proposed MZI design. Considering all the above-mentioned advantages, the proposed interferometric configurations based on low-symmetric PCs could be utilized for efficient photonic sensor applications that require controllable output power or sensing of gaseous and liquid substances.

We proposed a new method for designing graded index lens using liquid crystal infiltration into annular photonic crystals. Applying an external nonuniform voltage in the transverse direction perpendicular to the direction of light propagation yields different orientation of liquid crystal molecules inside the photonic crystal unit cells. As a result, a gradient refractive index was modulated. We numerically investigate focusing properties of the designed graded index structure using plane-wave expansion and finite-difference time-domain methods. The gradient refractive index profile was adjusted by varying the nonuniform voltage excitations, which consequently altered the focal distance of the graded index structure. A wide tuning range of 1856 nm was achieved for focal distance by the proposed graded index structure. This feature can be implemented for planning a flat lens with tunable focal distance based on electro-optic effect. These achievements may have future applications in some optical devices such as near-field imaging and scanning.

In this Letter, photonic crystal (PC) waveguide-based interferometer design is studied; spectral as well as temporal analyses have been conducted. Intentional structural modifications inside the interferometer trigger Fano resonances, allowing for extraordinary optical effects, such as enhanced beam recirculation and mode-order conversion. The proposed Mach–Zehnder–Fano interferometer is compatible with conventional silicon-on-insulator (SOI) technology and consists of two arms: the lower arm, with no point defects, creates continuum states, whereas the upper arm, including a Fano defect, creates discrete states. The PC waveguide channel with intentional point defects, which possess effective discreteness, creates the required phase retardation of the propagating beam, enabling Fano resonance excitations. Such a type of PC waveguide-based interferometer allows for the realization of compact mode-order converters with a broad 3 dB-bandwidth of 65 nm (at the wavelength range of λ = 1517 − 1582 nm) and efficient optical switching as well as sensing capabilities, operating at optical telecommunication bands, favoring inherent beam recirculation characteristics.

In this study, we present how to divide chromosome data sets into scalable hierarchical clusters. Diagnosis applications of chromosomal abnormalities to identify genetic diseases are mostly implemented with semi-automatic methods, which do not provide high-throughput and fast characterizations of patient specimens. However, selecting and managing specific features of chromosome data sets require dynamic and scalable data models. Here, we adapt the variations in sets to feature units as an effective tool for our dynamic/automated and scalable approach. This method enables geneticists to implement karyotyping techniques easily into an efficient identification of hereditary disorders or characterization of novel chromosomal alterations related with genetic diseases in a trusted/scalable manner. Furthermore, we explore physical limits of available application-specific integrated circuits (ASICs) and on-board computers (OBCs) to extract novel features of chromosomes via spectral analytics for real-time diagnosis and to overcome the bottlenecks of the computational complexity, as well.

In this study, we report a low-symmetric photonic crystal (PhC) structure that exhibits high coupling efficiency in a broadband frequency range with a tilted self-collimating capability. First, the analytical approach is implemented as a starting point, and the ideal configuration is chosen for the self-collimation effect, which is analytically supported by group velocity dispersion and third-order-dispersion calculations. Then, numerical analyses in both time and frequency domains are performed to the ideal PhC design, which possesses a strong self-collimating characteristic, even at huge incident angles within the operating frequencies. Later, experimental measurements are conducted in microwaves, and the existing self-collimation property is still preserved at longer wavelengths in the millimeter scale. The microwave experiment as well as numerical analyses indicate that the designed PhC self-collimator allows overcoming possible misalignment problems at the PhC - source interface and enables a strong broadband beam channeling with a high transmission. (C) 2018 Optical Society of America

Intensive researches in the area of metasurfaces have provided a new insight to obtain flat and compact optical systems. In this letter, we numerically show that, highly efficient tunable beam steering effect in transmission mode is achieved at wavelength λ = 550 nm using nematic liquid crystals (LCs) infiltrated into double sided metasurfaces. Using the electrooptical feature of LCs, the phase profile of the metasurfaces is controlled and thus, the transmitted beam is deflected within the range from -15° to 15° steering angles. Transparent dielectric materials are used in the designed structure that provides highly efficient beam-steering; the corresponding transmission efficiency is above 83% in the visible spectrum, which is another superiority of the proposed hybrid tunable structure over present plasmonic/metamaterial approaches. The designed metasurface still preserves its beam deflection property covering the visible spectrum and hence, such hybrid structure can be implemented for broadband electro-optically controllable beam steering applications.

Photonic and Phononic Properties of Engineered Nanostructures VIII (2018 ; San Francisco, United States), Low-symmetric photonic crystals (PCs) have a high level of tunability in terms of their iso-frequency contours or refractive indices via angular orientations as well as spatial variations of unit cell elements. This phenomenon brings along emerging extraordinary dispersion properties dependent to rotation and position of unit cells. In this study, we show that the electromagnetic waves propagating inside the low-symmetric waveguides can be exposed to phase delays by tuning the angular orientations of unit elements. In this way, low-symmetric PC waveguides based Mach-Zehnder Interferometers (MZIs) exhibiting controllable phase properties are designed. The investigated all-dielectric tunable interferometric systems are numerically analyzed in both frequency and time domains. Furthermore, by exploiting spectral sensitivity of proposed MZIs, conceptual demonstration of gas sensor systems is performed. The designed optical gas sensors have minimum selectivity of 200 nm/RIU even in the case of refractive index variation on the order of 10-4 RIU in analytes. Having these advantages, proposed interferometric configurations based on low-symmetric periodic structures may offer a significant alternative for photonic applications that require controllable output power or sensing of gaseous substances.

Different optimization algorithms have recently been utilized to design and improve the performance of many nanophotonic structures. We present the design of a compact photonic structure by an approach based on machine learning. Three-dimensional finite-difference time-domain method is integrated with a machine learning algorithm in order to design a photonic structure. In particular, a subwavelength focusing lens structure that operates at telecom wavelengths is designed to have desired beam properties such as subwavelength full-width at half-maximum value of 0.155 λ and suppressed side-lobe levels at focal point, where λ denotes the wavelength of incident light and equals to 1550 nm. The designed compact lens structure has the footprint of 2 × 1 μ m2 with a slab thickness of 280 nm, which is the smallest photonic lens for subwavelength focusing of light to date comparing to its conventional ones. The focusing mechanism of designed lens structure is explained with the help of applying discrete Fourier transform to the two-dimensional dielectric distribution of the structure. It is also shown that, due to its strong light confinement property, the designed lens structure can be used as a waveguide-to-waveguide optical coupling device with a beamwidth compression ratio of 10:1 by integrating a nanowaveguide with the width of 200 nm to the output surface of lens structure. Normalized transmission efficiency of the optical coupling device is calculated as high as 0.62 at the wavelength of 1550 nm. The outcomes of the presented study show that machine learning can be beneficial for designing efficient compact photonic structures., National Council for Scientific Research[116F182]

In this study, realization and applications of anisotropic zero-refractive-index materials are proposed by exposing the unit cells of photonic crystals that exhibit Dirac-like cone dispersion to rotational symmetry reduction. Accidental degeneracy of two Bloch modes in the Brillouin zone center of two-dimensional C-2-symmetric photonic crystals gives rise to the semi-Dirac cone dispersion. The proposed C-2-symmetric photonic crystals behave as epsilon-and-mu-near-zero materials (epsilon(eff) approximate to 0,mu(eff) approximate to 0) along one propagation direction, but behave as epsilon-near-zero material (epsilon(eff) approximate to 0, mu(eff )not equal 0) for the perpendicular direction at semi--Dirac frequency. By extracting the effective medium parameters of the proposed C-4- and C-2-symmetric periodic media that exhibit Dirac-like and semi-Dirac cone dispersions, intrinsic differences between isotropic and anisotropic materials are investigated. Furthermore, advantages of utilizing semi-Dirac cone materials instead of Dirac-like cone materials in photonic applications are demonstrated in both frequency and time domains. By using anisotropic transmission behavior of the semi--Dirac materials, photonic application concepts such as beam deflectors, beam splitters, and light focusing are proposed. Furthermore, to the best of our knowledge, semi--Dirac cone dispersion is also experimentally demonstrated for the first time by including negative, zero, and positive refraction states of the given material. Scientific and Technological Research Council of Turkey (TUBITAK) Turkish Academy of Sciences

We theoretically study the forward and backward plane wave illuminations of hemicylindrical dielectric particles with different radii and refractive indices. Near field effects providing strong field enhancement and narrow beam width are obtained from hemicylindrical particles, which can be associated with whispering gallery modes (WGMs) and photonic nano-jets (PNJs). It should be noted that existence of PNJ and WGM effects depending on forward/backward light illuminations is studied for the first time in alldielectric hemicylindrical particles. Compared to dielectric cylinders, hemicylindrical aided PNJs show relatively small influences of WGM regime, when exists, to PNJ behavior. Under the backward excitation, on the other hand, typical nano-jet is produced. The designed hemicylindrical structure could be implemented in high-resolution optical imaging and sensing applications., Hamza Kurt acknowledges the support of Turkish Academy of Sciences, Oleg V. Minin acknowledges the partial support by Mendeleev Scientific Fund of Tomsk State University, Project 8.2.08.2017.

Photonic and Phononic Properties of Engineered Nanostructures VIII (2018 ; San Francisco, United States), Photonic crystals ( PhCs) are artificial wavelength-scale periodic structures that enable the manipulation of light propagation and possess intriguing dispersive characteristics such as negative refraction, self-collimation, slow/ fast light and super-prism. Among these properties, here we present compact low-symmetric PhCs exhibiting S-vector super-prism effect with high diffraction ability. Each unit-cell of square lattice PhC structure includes two dielectric rods in air background and it provides a high-resolution super-prism effect for transverse-magnetic bands. Theoretical calculations of band structures as well as equi-frequency contours are conducted by solving Maxwell's equations with plane-wave expansion method to investigate the superprism effect of the proposed PhCs. Such asymmetric PhC configuration has a wide wavelength sensitivity from a/lambda = 0.610 to a/lambda= 0.628. Its operating frequency range provides also a huge angle magnification from 20.6 degrees to 59.9 degrees. In terms of diffraction ability, the proposed PhC structure overcomes the problems of irregular beam generation and irregular beam divergence in usual PhC structures. According to finite-difference time-domain calculations with 3 degrees angle of incidence, it is obtained that the light is diffracted in a range between 20.6 degrees and 59.9 degrees inside the structure with a high wavelength sensitivity. That effect could be used for wavelength demultiplexing applications. Moreover, the numerical time-domain calculations are made to verify the theoretical analyses. Depending on the incidence angle, the light propagating inside the PhC medium steers up/ down perfectly with a collimated behavior. Such highly wavelength sensitive self-collimated light diffraction property can be used to separate propagating beam at the output channels with low cross-talks in compact photonic integrated systems. Experimental verification of the intended superprism effect is also conducted in the microwave frequencies and a quite well wavelength sensitivity effect is observed.

We present theoretical studies on a tunable photonic nanojet (PNJ) created by adapting a shell and liquid crystal (LC) core architecture. The shell is made of indium tin oxide and the core is infiltrated with nematic LCs. The application of an external static electric field to the LCs modifies their refractive index, and this allows tuning the PNJ effect in the proposed system. In addition to nonresonant excitation, resonant PNJ excitation is also obtained from a hybrid structure. Both nonresonant and resonant internal field excitations of circular and elliptical PNJ configurations are examined by using a high-resolution finite-difference time-domain method. The calculated results indicate that the proposed PNJ configurations with tunable refractive indices lead to significant changes in some parameters such as decay length, focal distance, full width at half maximum and electric field intensity. Such PNJ designs can be employed in high-resolution optical sensors, optical trapping, and high-density data storage. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

We present an intrinsic polarization splitting characteristic of low-symmetric photonic crystals (PCs) formed by unit-cells with C-2 rotational symmetry. This behavior emerges from the polarization sensitive self-collimation effect for both transverse-magnetic (TM) and transverse-electric (TE) modes depending on the rotational orientations of the unit-cell elements. Numerical analyzes are performed in both frequency and time domains for different types of square lattice two-fold rotational symmetric PC structures. At incident wavelength of lambda = 1550 nm, high polarization extinction ratios with similar to 26 dB (for TE polarization) and similar to 22 dB (for TM polarization) are obtained with an operating bandwidth of 59 nm. Moreover, fabrication feasibilities of the designed structure are analyzed to evaluate their robustness in terms of the unit-cell orientation: for the selected PC unit-cell composition, corresponding extinction ratios for both polarizations still remain to be over 18 dB for the unit-cell rotation interval of theta = [40 degrees-55 degrees]. Taking all these advantages, two-fold rotationally symmetric PCs could be considered as an essential component in photonic integrated circuits for polarization control of light. Scientific and Technological Research Council of Turkey (TUBITAK) Turkish Academy of Sciences

In this study, a Mach-Zehnder interferometer (MZI) design is presented based on low-symmetric photonic crystal (PC) waveguides. As is known, breaking the translational or rotational symmetries of PC unit-cell may provide enhanced optical characteristics; for example, rotating the low-symmetric PC unit-cell around its axis, may support different phase indices (n(p)) at certain wavelengths without changing dielectric filling amount. Moreover, this phenomenon could be implemented to create the arms of MZI to obtain required phase difference at each section. However, purely symmetric PCs cannot satisfy that phase difference characteristic so that it is essential to change the optical path of the arms to obtain a required phase difference. Dependence of the interference effect on the incident wavelengths is also demonstrated for the proposed low-symmetric PCs, whereas the interference in high-symmetric PC-based MZIs is not directly depend on the incident wavelengths. A three-channel interferometer is also designed and its transmission behavior is analyzed depending on the intentional modifications of the PC waveguide channels. Phase indices' change with respect to the PC unit-cell orientations may enable to design compact and efficient PC-based MZIs, which is not possible using high-symmetric PCs.

A novel concept of polarization beam splitting with high polarization extinction ratio is proposed based on the polarization sensitive self-collimation feature of symmetry reduced photonic crystals. The idea utilizes self-collimation mechanism and rotated isofrequency contours arising due to the deliberately implemented symmetry reduction in the photonic structure. Square lattice of low-symmetric rectangular air holes in dielectric background are numerically analyzed in both frequency and time domains. The operating bandwidth of the device is Delta lambda = 53 nm. At lambda = 1.55 mu m, polarization extinction ratios are similar to 23 and similar to 18 dB for transverse electric and transverse magnetic ports, respectively. The investigated device is 46.4 mu m x 12.4 mu m in size and based on a uniform, planar, and homogenous structure. Therefore, there is no need for an additional splitting assistance to separate the two orthogonal polarizations. Possible fabrication imperfections are also analyzed and it is observed that polarization extinction ratios stay above 17 dB when error percentage is around 5.5%. With having these advantages, symmetry reduced photonic crystal-based polarization beam splitters can be a good candidate for optical communication applications., The work of U. G. Yasa and I. H. Giden was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project 115R036. The work of H. Kurt was supported in part by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project 115R036 and in part by Turkish Academy of Sciences.

We perform numerical analyses of tunable graded index photonic crystals based on liquid crystals. Light manipulation with such a photonic medium is explored and a new approach for active tuning of the focal distance is proposed. The graded index photonic crystal is realized using the symmetry reduced unit element in two-dimensional photonic crystals without modifying the dielectric filling fraction or cell size dimensions. By applying an external static electric field to liquid crystals, their refractive indices and thus, the effective refractive index of the whole graded index photonic crystal will be changed. Setting the lattice constant to a=400 nm yields a tuning of 680 nm for focal point position. This property can be used for designing an electro–optic graded index photonic crystal-based flat lens with a tunable focal point. Future optical systems may have benefit from such tunable graded indexlenses. © 2016 Elsevier B.V.

The European Conference on Lasers and Electro-Optics (2017 : Munich; Germany), [No abstract available]

Integrated photonic systems require efficient, compact, and broadband solutions for strong light coupling into and out of optical waveguides. The present work investigates an efficient optical power transferring the problem between optical waveguides having different widths of in/out terminals. We propose a considerably practical and feasible concept to implement and design an optical coupler by introducing gradually index modulation to the coupler section. The index profile of the coupler section is modulated with a Gaussian function by the help of striped waveguides. The effective medium theory is used to replace the original spatially varying index profile with dielectric stripes of a finite length/width having a constant effective refractive index. 2D and 3D finite-difference time-domain analyzes are utilized to investigate the sampling effect of the designed optical coupler and to determine the parameters that play a crucial role in enhancing the optical power transfer performance. Comparing the coupling performance of conventional benchmark adiabatic and butt couplers with the designed striped waveguide coupler, the corresponding coupling efficiency increases from approximately 30% to 95% over a wide frequency interval. In addition, to realize the realistic optical coupler appropriate to integrated photonic applications, the proposed structure is numerically designed on a silicon-on-insulator wafer. The implemented SOI platform based optical coupler operates in the telecom wavelength regime (lambda = 1.55 mu m), and the dimensions of the striped coupler are kept as 9.77 mu m (along the transverse to propagation direction) and 7.69 mu m (along the propagation direction) where the unit distance is fixed to be 465 nm. Finally, to demonstrate the operating design principle, the microwave experiments are conducted and the spot size conversion ratio as high as 7.1:1 is measured, whereas a coupling efficiency over 60% in the frequency range of 5.0-16.0 GHz has been also demonstrated. Published by AIP Publishing. Scientific and Technological Research Council of Turkey (TUBITAK) Turkish Academy of Sciences

We present the optical properties of a new type of photonic crystal (PC) named star-shaped PC (STAR-PC) with anomalous equi-frequency contours. Intentionally introducing low-symmetry in the primitive unit cell gives rise to progressively tilting flat contours, which are observed in the fifth band of the transverse magnetic mode. Due to the intrinsic dispersive feature of the proposed PCs, i.e. tilted self-collimation, the incident signal with different wavelengths can be successfully separated in a spatial domain without introducing any corrugations or complexities inside the structure. We show numerical investigations of wavelength selective characteristic of the proposed PC structure in both time and frequency domains. The STAR-PC approach can be considered a good candidate for the wavelength division applications in the design of compact photonic integrated circuits. For the purpose of wavelength separation implementations, the proposed structure may operate within the wavelength interval of 1484.5-1621.5 nm with a broad bandwidth of 8.82%. The corresponding inter-channel crosstalk value is as low as -19 dB and the calculated transmission efficiency is above 97%. (C) 2013 Elsevier B.V. All rights reserved.

In this paper, a novel technique for spatial wavelength division using graded index photonic crystals (GRIN PCs) is proposed. The designed GRIN PC structure with hyperbolic-secant refractive index profile at a fixed frequency generates spatial shifts in the longitudinal direction with respect to different incident wavelengths so that distinct path trajectories are followed by propagating beams through the graded medium. Due to gradual variation of the refractive index profile (incremental decrease), an incident beam with an appropriately selected wavelength undergoes continuing refraction and finally, total internal reflection (TIR) occurs at the turning point. Due to the wavelength-dependency characteristic of GRIN PCs, TIR takes place at different positions for different wavelengths and thus, light wave emanates from the GRIN medium at different locations with different exit angles. It is revealed that the designed structure can work in three distinct frequency regimes and is able to separate a certain number of incident beams with different wavelengths, viz. from three to seven different wavelengths. This condition enables the deployment of the GRIN PC configuration for the design of wavelength selective media.

We investigate dispersive properties of two dimensional photonic crystal (PC) called star-shaped PC (STAR-PC) in order to succeed super-collimation over a broad bandwidth. Both time- and frequency-domain numerical methods are conducted. Due to introduced low-symmetry in the primitive cell, flat contours are observed at the fifth band for transverse magnetic mode. The proposed structure supports a super-collimation effect over a broad wavelength range between 1443 nm and 1701 nm with a bandwidth of Delta omega = 16.42%. The intrinsic characteristic of STAR-PC provides in-plane beam propagation with a limited diffraction length of 120a, where a is the lattice constant. By mean's of STAR-PC, one may realize super-collimation based single-mode optical devices with a low insertion loss, reduced dispersion and wide bandwidth. (C) 2012 Elsevier B.V. All rights reserved.

We propose a new type of add-drop microring resonator made of gain and loss materials. Microring resonators are compact, narrow band, and optical channel dropping filters. In such linear systems, light transmission to side-coupled signal waveguides is always symmetric. However, we prove that properly arranging a gain and loss modulation in the microring resonator provides a new functionality: asymmetric transmission; so that different resonant modes can be promoted depending on the input channel. This can be achieved when the resonator holds parity-time (PT-) symmetry, with periodic gain-loss and index modulations. PT-symmetry in optics generally requires that the index and gain-loss modulations are dephased by a quarter of the wavenumber of the modulation. Besides, we show that a simple half-gain half-loss microring also produces analogous results to a periodic PT-symmetric system. The results are numerically proved and also accounted by a simple analytical model. The effect of using complex modulated resonators with smaller periodicities is also analyzed., The work of M. Botey, R. Herrero, and K. Staliunas was supported by the Spanish Ministerio de Educacion y Ciencia under Project FIS2011-29734-C02-01. The work of H. Kurt was supported in part by the Turkish Academy of Sciences.

In this paper, we propose a novel photonic crystal sensor based on refractive index sensing method. The proposed photonic crystal sensor design has a T-shaped sensing slot region to inject bio-material samples with different refractive index values between 1.00 and 1.35. The corresponding highest refractive index unit (RIU) sensitivity of the designed photonic crystal is numerically calculated as 1016 nm/RIU. The designed photonic crystal sensor can be especially utilized for analysing different gas contaminations and diabetic blood samples in the healthcare sector.

We propose compact S-vector superprism providing broadband wavelength sensitivity within a/λ = 0.610-0.635, where "a" is the lattice constant, λ is the incident wavelength, and S denotes the Poynting vector. The reported configuration overcomes strong beam divergence and complex beam generation due to the self-collimation ability of the low symmetric primitive photonic crystal (PhC) cells. Analytical calculations of equi-frequency contours, photonic band structures, and group velocity dispersions are performed by solving Maxwell's equations and using the plane wave expansion method. Besides, finite-difference time-domain analyses are also conducted. The designed superprism induces large refracted angle variation for different frequencies when the incident angle is fixed: 4% change of incident frequencies results in approximately 40° deflected angle difference with a maximum 68.9° deflection angle inside the PhC. Meanwhile, for a fixed incident wavelength, a large output variation occurs if the incident angle is altered. Microwave experimental results are found to be in good agreement with the numerical analyses. The authors M.G. and H.K. gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK) with Project No. 115R036. H.K. also acknowledges the partial support of the Turkish Academy of Sciences.

17th International Conference on Transparent Optical Networks (2015 : Hungary), We propose a new type of add-drop Micro ring resonator that is made up of gain and loss materials. In all-dielectric linear systems, light transmission is reciprocal: A symmetric transmission spectrum is observed when an incident source is pumped from one side and output power detected in the other side or vice versa. On the other hand, Parity-time (PT) symmetric optical systems that consist of balanced gain-loss modulation possess unique characteristics such as unidirectional beam propagation, asymmetric light transmission and nonreciprocal chirality. In this study, we proved numerically that PT symmetric optical resonator designs can be achieved by properly arranging the gain-loss modulation so that different resonant modes can be promoted depending on the direction of source incidence. © 2015 IEEE., ADVA,Ericsson,Silicon Labs

We propose a new approach for the realization of a graded index (GRIN) medium using a symmetry reduced unit element in photonic crystals. An index gradient on the order of ?n = 0.16 is achieved without modifying the filling fraction or cell size dimensions. Various beam manipulation techniques can be implemented with such a GRIN medium. We show that designed GRIN structure may effectively focus an incident beam over wide bandwidth. The arrangement of the photonic crystal (PC) elements within unit cells exhibits structural order which is helical along the transverse to propagation direction. The designed GRIN PC structurally resembles the molecular orientation of cholesteric liquid crystals. © 2015 Optical Society of America.

In this manuscript, we propose the design of an inhomogeneous artificially created graded index (GRIN) medium to enrich the optical device functionalities of light by using periodic all-dielectric materials. Continuous GRIN profile with hyperbolic secant index distribution is approximated using two-dimensional photonic crystal (2D PC) dielectric rods with a fixed refractive index. The locations of each individual cell that contain dielectric rods of certain radii are determined based on the results of the frequency domain analysis. The desired index distribution is attained at long wavelengths using dispersion engineering approach. The frequency response of the transmission spectrum exhibits high transmission windows appearing at both larger and smaller wavelengths regions. Two regions are separated by a local band gap that blocks the incident light for a certain frequency interval. Light manipulation characteristics such as focusing, de-focusing and collimation are systematically and quantitatively compared for artificially designed GRIN medium within low and high frequency regimes. We show different field manipulation capabilities and focal point movement dynamics of the GRIN medium by special adjustment of the length of the structure. In addition, an analytical formulation based on ray theory is derived to investigate the focusing, de-focusing and collimation properties of proposed GRIN medium. The analytical approach utilizes Ray theory and computational tools are based on plane wave expansion and finite-difference time-domain methods. Implementing the GRIN medium by periodic optical materials provides frequency selectivity and strong focusing effects at higher frequency region. The designed structure can be used in integrated nanophotonics as a compact optical element with flat surfaces. (C) 2014 Elsevier B.V. All rights reserved.

Cataloged from PDF version of article. We propose a simple realistic two-dimensional complex parity-time-symmetric photonic structure that is described by a non-Hermitian potential but possesses real-valued eigenvalues. The concept is developed from basic physical considerations to provide asymmetric coupling between harmonic wave components of the electromagnetic field. The structure results in a nonreciprocal chirality and asymmetric transmission between in- and out-coupling channels into the structure. The analytical results are supported by a numerical study of the Bloch-like mode formations and calculations of a realistic planar semiconductor structure. © 2015 American Physical Society.

Direction-dependent light transmission is a remarkable phenomenon owing to its great potential to be used in optical communication processing systems such as optical diodes, isolators and rectifiers. All these applications require optical reciprocity breaking mechanisms such as magneto-optical effect. Keeping the reciprocity intact, it is possible to manipulate the amount and spatial form of the two oppositely propagating lights exiting from a passive photonic medium. In this paper, a photonic crystal diffraction grating (PCDG) configuration is studied for the investigation of asymmetric light transport due to the spatial inversion symmetry breaking in the designed compact all-dielectric PC heterostructure. Thanks to the periodic corrugations at the back-surface of the designed structure, the backward transmission of the zero-order diffracted wave is notably suppressed while the efficient unidirectional forward transmission is achieved. Numerical calculations show that up to 73% of the incoming electromagnetic energy is transmitted in the forward illumination whereas it reduces down to a value of 6% (which corresponds to 10.85 dB beam suppression) in the case of backward illumination. That asymmetric light transmission leads to a contrast ratio (CR) of above 0.55 (CR = (T +x - T -x)/(T +x + T -x), in which T -x and T +x are the transmission efficiencies in the -x and +x directions, respectively). The highest contrast ratio of CR = 0.99 is calculated at the incident frequency of a/λ = 0.5338 having the forward and backward transmissions of {T +x,T -x} = {42%,0.1%}, which corresponds to the beam suppression of 26.23 dB. Furthermore, the proposed PCDG exhibits the diffraction grating effect at the considerable range of angle of incidence up to ±20° at certain frequencies indicating that the proposed grating system is durable to source misalignments., Türkiye Bilimler Akademisi

Much attention has been paid to photonic applications based on periodic media. Meanwhile, quasi-periodic and disordered mediahave extended the research domain and provided additional novelties for manipulating and controlling light propagation. This review article attempts to highlight the benefits of symmetry reduction in highly symmetric periodic photonic media, and applies the concept of chirality to all-dielectric materials arranged in special orders. Two-dimensional periodic structures known as photonic crystals (PCs) are highly symmetric in terms of structural patterns, due to the lattice types and shape of the elements occupying the PC unit-cell. We propose the idea of intentionally introducing reduced-symmetry, to search for anomalous optical characteristics so that these types of PCs can be used in the design of novel optical devices. Breaking either translational or rotational symmetries of PCs provides enhanced and additional optical characteristics such as creation of a complete photonic bandgap, wavelength demultiplexing, super-collimation, tilted self-collimation, and beam deflecting/routing properties. Utilizing these characteristics allows the design of several types of photonic devices such as polarization-independent waveguides, wavelength demultiplexers, beam deflectors, and routers. Moreover, reducing the symmetry in the PC unit-cell scale produces a novel feature in all-dielectric PCs that is known as chirality. On the basis of above considerations, it is expected that low-symmetric PCs can be considered as a potential structure in photonic device applications, due to the rich inherent optical properties, providing broadband operation, and being free of absorption losses. © 2014, European Optical Society (EOS). All rights reserved.

27th IEEE Photonics Conference (2014 :San Diego; United States), Graded Index Photonic Crystals (GRIN PhCs) are artificial periodic materials that possess gradually varying effective refractive indices. GRIN profiles can be formed by adjusting the radii or the locations of PhC unit cells. GRIN PhCs exhibit several intriguing characteristics which can be listed as demultiplexing [1], mode-order conversion [2], asymmetric light propagation [3], compact lensing [4], and coupling between waveguides of different widths [5]. In addition to pure GRIN effects, the effects arising from the combinations of PhC properties (photonic bandgaps) can even enrich the possibilities of light manipulations. As a result, broad band transmission spectrum is combined with the directional band gaps [5]. Angular selectivity also can be utilized to separate different wavelengths [1]. Lastly, point and line defects can be introduced to have cavity and waveguides with GRIN PhC. © 2014 IEEE.

We propose a mode conversion method that enables transformation of the propagating mode from fundamental to higher-order modes by utilizing asymmetric graded index (A-GRIN) structures. Refractive index variations of two different asymmetric gradient profiles, i.e., exponential and Luneburg lens profiles, have been approximated by two-dimensional photonic crystals (PCs). The basic structure is composed of constant radii with different lattice sizes. The designed GRIN mode converters provide relatively high transmission efficiency in the spectral region of interest and achieve the transformation in compact configuration. Numerical approaches utilizing the finite-difference time-domain and plane wave expansion methods are used to analyze the mode conversion phenomenon of proposed GRIN PC media. Analytical formulation based on ray theory is outlined to explore both ray trajectories and the physical concept of a wavefront retardation mechanism. (C) 2013 Optical Society of America

There have been huge efforts performed on the study of photonic crystals due to their potential to manipulate the flow of light waves at the optical domain. One of the precious features of the photonic crystals is that they have photonic band gaps, i.e. frequency bands in which optical modes are suppressed to exist. The creation of complete photonic band gap is an important concept especially for the design of polarization-insensitive optical devices. There are various studies targeting the generation of larger band gaps in two-dimensional photonic crystals by means of engineering the lattice geometry or by a change of the shape and orientation of the unit cells of the structure. In the present work, we study the creation of complete band gaps by breaking the structural symmetry of the annular photonic crystals which is called as modified annular photonic crystals. This new structure enables us to engineer dispersion characteristics of photonic crystals that facilitate the design of configurable polarization-insensitive optical devices for different practical applications such as self-collimation waveguides, defect-based linear waveguides, and beam splitters.

In this paper complete photonic bandgap (PBG) and iso-frequency contours (IFCs) of two-dimensional modified annular photonic crystals (MAPC) for four different configurations are numerically studied and calculated by applying plane wave expansion method. The effects of opto-geometric parameters of the designed unit-cell structures are clearly demonstrated in terms of opening frequency gaps and appearing tilted band curves. Optimal structures with large PBGs are reported. The absolute gap can be increased to a maximum value of Delta omega/omega = 0.1766(2 pi c/a), where a is the lattice constant and c is the speed of light. The incorporation of additional parameters inside the unit cell of photonic crystal enables an extra degree of freedom for controlling the flow of light even in the absence of structural defects. The finite-difference time-domain method is utilized to depict the MAPC's light deflection and guiding characteristics. These proposed structures are likely to be promising candidates for applications that require polarization insensitivity due to providing large complete PBGs and possessing special IFCs. (C) 2012 Optical Society of America

A novel (to our best knowledge) type of photonic crystal (PC) structure called modified annular PC (MAPC) that is composed of dielectric rods with off-centered air holes is thoroughly studied. The plane wave expansion method is applied for spectral analysis. A complete photonic bandgap region with a considerable value of gap width Delta omega/omega = 7.06% is achieved by optimizing the structural parameters of the proposed periodic medium. By introducing geometrical asymmetry to the primitive cell of PC, we engineer the dispersion properties of the proposed photonic structure such that conventional equifrequency contours for the second band can be transformed into tilted rectangular shapes. This feature enables us to demonstrate the polarization insensitive tilted self-collimation effect. A hybrid structure composed of dielectric nanowire and MAPCs is offered to obtain a high degree of polarization independent guiding of light. The two-dimensional finite-difference time-domain method is carried out to verify the light guiding efficiencies. Polarization insensitive optical functionalities achieved by MAPC structure can be deployed in integrated optical circuits. (C) 2012 Optical Society of America

We present optical properties of crescent-shaped dielectric nano-rods that comprise a square lattice periodic structure named as crescent-shaped photonic crystals (CPC). The circular symmetry of individual cells of periodic dielectric structures is broken by replacing each unit cell with a reduced symmetry crescent shaped structure. The created configuration is assumed to be formed by the intersection of circular dielectric and air rods. The degree of freedom to manipulate the light propagation arises due to the rotational sensitivity of the CPC. The interesting dispersion property of designed CPC occurs due to the anisotropic nature of the iso-frequency contours that yield tilted self-collimated wave guiding. Furthermore, this feature allows focusing, routing, splitting and deflecting light beams along certain routes which are independent of the lattice symmetry directions of regular PCs. The propagation direction of light can be tuned by means of the opening angle of the crescent shape. Finally, the property of being all-dielectric structure ensures the absence of optical absorption losses that are reminiscent of employed metallic nano-particles. (C) 2012 Optical Society of America

Nanophotonic wire waveguides play an important role for the realization of highly dense integrated photonic circuits. The miniaturization of optoelectronic devices and realization of ultra-small integrated circuits strongly demand compact waveguide branches. T-shaped versions of nanophotonic wires are the first stage of both power splitting and optical-interconnection systems based on guided-wave optics; however, the acute transitions at the waveguide junctions typically induce huge bending losses in terms of radiated modes. Both 2D and 3D finite-difference time-domain methods are employed to monitor the efficient light propagation. By introducing appropriate combinations of dielectric posts around the dielectric-waveguide junctions within the 4.096μm×4.096μm region, we are able to reduce the bending losses dramatically and increase the transmission efficiency from low values of 18% in the absence of the dielectric posts to approximately 49% and 43% in 2D and 3D cases, respectively. These findings may lead to the implementation of such T-junctions in near-future high-density integrated photonics to deliver optical-clock signals via H-tree network.

To provide asymmetric propagation of light, we propose a graded index photonic crystal (GRIN PC) based waveguide configuration that is formed by introducing line and point defects as well as intentional perturbations inside the structure. The designed system utilizes isotropic materials and is purely reciprocal, linear, and time-independent, since neither magneto-optical materials are used nor time-reversal symmetry is broken. The numerical results show that the proposed scheme based on the spatial-inversion symmetry breaking has different forward (with a peak value of 49.8%) and backward transmissions (4.11% at most) as well as relatively small round-trip transmission (at most 7.11%) in a large operational bandwidth of 52.6 nm. The signal contrast ratio of the designed configuration is above 0.80 in the telecom wavelengths of 1523.5-1576.1 nm. An experimental measurement is also conducted in the microwave regime: A strong asymmetric propagation characteristic is observed within the frequency interval of 12.8 GHz-13.3 GHz. The numerical and experimental results confirm the asymmetric transmission behavior of the proposed GRIN PC waveguide. (C) 2014 AIP Publishing LLC.

27th IEEE Photonics Conference (2014 :San Diego; United States), We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background. © 2014 IEEE.

In this paper, we propose and design a new type of an integrated optical sensor that performs sensing in a wide wavelength range corresponding to mid-infrared (mid-IR) spectrum. By engineering the structural parameters of square-lattice photonic crystal (PC) slab incorporated with a T-shaped air-slot, strong light confinement and interaction with the analytes are assured. Numerical analyses in the time and frequency domain are conducted to determine the structural parameters of the design. The direct interaction between the slot waveguide mode and the analyte infiltrated into the slot gives rise to highly sensitive refractive index sensors. The highest sensitivity of the proposed T-slotted PC sensor is 1040 nm/RIU within the range of analytes' refractive indices n=1.05-1.10, and the overall sensitivity corresponding to the higher refractive index range of n=1.10-1.30 is around 500 nm/RIU. Moreover, for a realistic PC slab structure, we determined an average refractive index sensitivity of 530 nm/RIU within the range of n=1.10-1.25 and an average sensitivity of 390 nm/RIU within the range of n=1.00-1.30. Furthermore, we speculate on the possible approach for the fabrication and the optical characterization of the device. The assets of the device include being compact, having a feasible measurement and fabrication technique, and possessing label-free sensing characteristic. We expect that the presented work may lead to the further development of the mid-IR label-free biochemical sensor devices for detection of various materials and gases in the near future. (C) 2017 Elsevier B.V. All rights reserved., M.T. gratefully acknowledges the support of the TED University Scientific Research Project with Project No: 16A303. H.K. acknowledges partial support from the Turkish Academy of Sciences. M.T., Z.H., H.K. and K.S. also acknowledge partial support of NATO SPS-985048 grant.

3rd Dynamics Days South America Conference (2014 : Valparaiso; Chile), We propose a 2-dimensonal PT-symmetric photonic honeycomb structure that supports chiral Block-likemodes being its excitation input and frequency dependent. We show that while the fundamental resonant frequency excites the counterclockwisemode, the clockwisemode is excited at the corresponding second harmonic frequency from the same input channel. The geometry is derived as the simplest nontrivial extension from 1-dimensional PT-symmetric systems to provide asymmetric coupling between harmonic wave components of the electromagnetic field. The PT-symmetric honeycomb is generated by a closed set of three lattice vectors that enable the simultaneous resonance of two disjoint triads of wavevectors in a circular coupling. As a basic effect, we numerically show the measurable asymmetric transmission of Gaussian light beams incident on such a finite-sized structure with a hexagonal shape, at the fundamental and second harmonic resonant frequencies. © Springer International Publishing Switzerland 2016.