Mr. Bilgehan B. Oner Profile

Bilgehan B. Oner

at TOBB Univ of Economics and Technology

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Publications (3)

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Proceedings Article | 2 May 2014 Paper

Polarization independent nanobeam cavity tuning using annular photonic crystals

M. Can, B. Oner, H. Kurt

Proceedings Volume 9127, 912716 (2014) https://doi.org/10.1117/12.2052427

KEYWORDS: Waveguides, Dielectric polarization, Photonic crystals, Dielectrics, Polarization, Finite-difference time-domain method, Magnetism, Inspection, Optical filters, Structural design

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Nanobeam cavity waveguides have drawn great attention of the researchers due to being a useful optical platform for several applications, e. g. optical switching and filtering.1 Almost all of the past studies investigated high quality (Q) factors without considering polarization independency. In the literature Zhang et al. proposed a device that enables high Q for both transverse electric (TE) and transverse magnetic (TM) modes for a specific frequency.2 In our study we demonstrate a three-dimensional study of polarization independent nanobeam cavity waveguide that consists of annular photonic crystals (PCs) showing similar optical properties for both TE and TM modes.3 Besides, a detailed analysis of the shift of the overlapped frequency is investigated with respect to height and width variation of the nanobeam structure. The designed waveguide is composed of 12 air holes and 4 annular PCs located in the Silicon (nSi=3.46). The radii of all air holes in the structure are 0.36a. The annular PCs at the interior section have inner dielectric radii of 0.18a and the outer ones have inner dielectric radii of 0.20a. Silica (nSilica=1.52) material is used as a substrate. The width and height of the waveguide may be tuned in order to obtain high Q factors at the desired frequency for both polarizations. In our analysis, we investigated the relation between widths, height and cavity frequency for both TE and TM cases. Obtained frequencies are fitted to cubic polynomials of the structural parameters width and height. Overlapped frequency curve is revealed by an equalization of the polynomials of TE and TM resonant frequencies. The findings elucidate the effect of the parameters on the overlap mechanism of resonant mode matching for both polarizations.

Proceedings Article | 2 May 2014 Paper

Partial cloaking by graded index photonic crystals

Bilgehan Oner, Melih Can, Hamza Kurt

Proceedings Volume 9127, 912708 (2014) https://doi.org/10.1117/12.2052494

KEYWORDS: GRIN lenses, Waveguides, Refractive index, Photonic crystals, Light wave propagation, Dielectrics, Geometrical optics, Lead, Radio propagation, Lenses

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Since the first proposal of the idea of optical cloaking, huge research effort has been spent to implement hiding objects. We propose a broad band all-dielectric partial (unidirectional) cloaking device that hides arbitrary shaped objects. The cloaking structure is designed utilizing graded index (GRIN) photonic crystals. Refractive index distribution of the structure is chosen as a hyperbolic secant profile. In order to generate desired index profiles, both low and high dielectric backgrounds are chosen. The main principle of the cloaking in the study is separating the beam into two main parts while propagating through the composite device. Each part of the separated beam is strongly focused at the center of the stacked GRIN devices. Then these beams diverge and converge repeatedly without deteriorating the planar input field profile. This mechanism dramatically reduces the intensity at the center of the device. Therefore, existence of an object at the cloaked region almost does not affect wave front of the exiting beam due to this special light manipulation mechanism. In this manner, an observer cannot detect the hidden object. GRIN medium is a special type of inhomogeneous environment and light propagation is greatly affected by the presence of GRIN. Any partial cloaking solution as long as being practical and broadband in nature can be preferred. In this case, material selection and easy transferring the design to other electromagnetic spectrum regions become crucial. Therefore, the proposed idea in this work collects these desirable features.

SPIE Journal Paper | 15 October 2013 Open Access

Optical analysis of human eye using electromagnetic wave theory

Melih Can, Bilgehan Oner, Hamza Kurt

JBO, Vol. 18, Issue 10, 105006, (October 2013) https://doi.org/10.1117/12.10.1117/1.JBO.18.10.105006

KEYWORDS: Eye, GRIN lenses, Eye models, Refractive index, Retina, Cornea, Monochromatic aberrations, Electromagnetic radiation, Crystals, Radio propagation

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We present a two-dimensional electromagnetic analysis of light propagation through the human eye to examine the eye’s optical properties. The electromagnetic approach has intriguing advantages over the conventional and frequently implemented ray optics analysis. The chromatic, spherical, and coma aberrations and the intensity of the focused light at the retina are computed in this work via full-wave analysis. We also investigate the effects of the cornea’s and lens’s curved structures on the focusing mechanism. The focal length and chromatic and spherical aberrations are observed to change owing to age-related refractive index variation in the lens. In addition, the effects of the lens and curvatures of the human eye on focusing are analyzed. Consequently, for both young and old human eye lenses, the differences due to the aberration variations, curvature surfaces, and gradient index are explored by the wave approach. The intensity distributions on the retina for both on- and off-axis illumination are calculated. A strong correlation between the locations of the nerve fibers and the intensity distribution is confirmed. On the basis of the findings, we can conclude that visual impairment due to deterioration of the human eye structure is more dramatic than that due to aging.

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