Hamza Kurt 교수

We explore two-dimensional triangular lattice photonic crystals composed of air holes in a dielectric background which are subject to a graded-index distribution along the direction transverse to the propagation. The proper choice of the parameters such as the input beam width, gradient coefficient, and the operating frequency allow the realizations of the focusing (lens) and guiding (waveguide) effects upon which more complex optical devices such as couplers can be designed. Numerical results o

The propagation of terahertz waves in two-dimensional photonic-crystal waveguides was studied computationally to investigate the effects of introducing small quantities of molecules, such as deoxyribonucleic acid, into selected air holes for sensor applications. Comparison with bulk systems shows that photonic-crystal waveguides are promising for biochemical sensing.

A new type of two-dimensional photonic-crystal (PC) structure called annular PC composed of a dielectric-rod and a circular-air-hole array in a square or triangular lattice such that a dielectric rod is centered within each air hole is studied. The dielectric rods within the air holes greatly modify the dispersion diagram of the photonic crystal despite the fact that the percentage of volume occupied by the dielectric rods may be small (<12%). Increasing the radius of the inner-dielectric rod, s

We describe an approach to implement graded index (GRIN) structures using two-dimensional photonic crystals (PCs). The lattice spacing along the transverse direction to propagation is altered and we show, both theoretically and experimentally, that such a spatial perturbation is an effective way to obtain GRIN PC. The response of the structure to spatially wide incident beams is investigated and strong focusing behavior is observed. The large spot size conversion ratio can be attainable and is m

We report numerical and experimental investigations of asymmetric light propagation in a newly designed photonic structure that is formed by creating a chirped photonic crystal (PC) waveguide. The use of a non-symmetric distribution of unit cells of PC ensures the obtaining of asymmetric light propagation. Properly designing the spatial modulation of a PC waveguide inherently modifies the band structure. That in turn induces asymmetry for the light's followed path. The investigation of the trans

We investigate slow light propagation in monomode photonic crystal waveguides with different spectral features such as constant group index, high bandwidth and low group velocity dispersion. The form of the waveguide mode alters dramatically and spans three different spectral intervals by tuning the size of the boundary holes. Namely, slope of the band gap guided mode changes sign from negative to positive toward the Brillouin zone edge. In between there is a transition region where modes have n

Beam splitters play important roles in several optical applications, such as interferometers, spectroscopy, and optical communications. In this study, we propose and numerically examine polarization-insensitive beam splitters utilizing two-step phase gradient all-dielectric metasurfaces in the visible spectrum. The metasurface is made of periodically arranged binary unit cells, and phase difference between neighboring unit cells on the surface is 180 deg. The metasurface is shown to have a speci

We present a detailed study of coupled-resonator optical waveguide (CROW) based sensors for biochemical sensing. The sensitivity dependence on the CROW structure parameters, such as intercavity distance and cavity type, is investigated for the effects in the THz region of the EM spectrum of introducing small quantities of molecules, such as DNA, in the holes. Introducing the absorptive material into the low-index medium greatly affects the shape of the propagating modes of the CROW and the trans

We explore beam-bending properties of graded index (GRIN) waveguide with hyperbolic secant profile. The transmission efficiency and bandwidth features are extracted for GRIN photonic crystal (PC) media composed of dielectric rods. Light guiding performance of the GRIN PC medium is analyzed for 90° and 180° waveguide bends. The finite-difference time-domain method is deployed to investigate the performance of the designed GRIN waveguides. By the help of proposed photonic configuration, bending of

We explore an efficient method to couple light from a dielectric medium into a two-dimensional photonic-crystal waveguide (PCW). This is achieved by inserting a graded-index photonic crystal (PC) between a dielectric waveguide and a conventional PCW obtained by removing one row of air holes along the TK direction in a triangular-lattice PC. Effective mode transformation is achieved with a spot-size conversion ratio of 12:1. The low transmission efficiency (30%) that occurs in a direct coupling f

We present the design and analysis of a novel reconfigurable photonic-crystal waveguide (PCW). The predefined waveguide is the result of the refractive-index variation of three rows of holes that can be obtained by the infiltration of liquids within what are otherwise air holes in a two-dimensional triangular-lattice photonic crystal. We compute the power transmission through the reconfigurable PCWs as well as through arbitrary waveguide bends. The advantages of writing reconfigurable PCW of a m

Large and periodically corrugated optical waveguide structures are shown to possess specific modal regimes of slow-light propagation that are easily attainable. The very multimode nature of the coupling is studied by employing coupled-mode theory and the plane-wave expansion method. Given a large enough light cone, associated with a surrounding medium with low enough refractive index, we notably identify a critical slowdown regime with an interesting bandwidth-slowdown product. Essential feature

In modern optical applications, it has become an important need to flow light unidirectionally. An optical diode realizes this task as an electrical counterpart manipulates the flow of electrons in semiconductor materials. In this study, we show a broadband and polarization-independent optical diode-like mechanism in a metasurface configuration in the visible spectrum. The approach is passive such that the operating principle does not depend on any type of external biasing scheme. The constitute