Browsing by Subject "Refraction"

Now showing 1 - 19 of 19

Open Access
Asymmetric transmission in prisms using structures and materials with isotropic-type dispersion
(Optical Society of America, 2015) Gundogdu, F. T.; Serebryannikov, A. E.; Cakmak, A. O.; Özbay, Ekmel
It is demonstrated that strong asymmetry in transmission can be obtained at the Gaussian beam illumination for a single prism based on a photonic crystal (PhC) with isotropic-type dispersion, as well as for its analog made of a homogeneous material. Asymmetric transmission can be realized with the aid of refraction at a proper orientation of the interfaces and wedges of the prism, whereas neither contribution of higher diffraction orders nor anisotropic-type dispersion is required. Furthermore, incidence toward a prism wedge can be used for one of two opposite directions in order to obtain asymmetry. Thus, asymmetric transmission is a general property of the prism configurations, which can be obtained by using simple geometries and quite conventional materials. The obtained results show that strong asymmetry can be achieved in PhC prisms with (nearly) circular shape of equifrequency dispersion contours, in both cases associated with the index of refraction 0 < n < 1 and n > 1. For the comparison purposes, results are also presented for solid uniform nonmagnetic prisms made of a material with the same value of n. It is shown in zero-loss approximation that the PhC prism and the ultralow-index material prism ( 0 < n < 1) can replace each other in some cases without affecting the scenario of asymmetric transmission. Moreover, the PhC prism and the solid dielectric prism can show the same scenario at n > 1. Possible contributions of scattering on the individual rods and diffraction on the wedge to the resulting mechanism are discussed. Analogs of unidirectional splitting and unidirectional deflection regimes, which are known from the studies of PhC gratings, are obtained in PhC prisms and solid uniform prisms, i.e. without higher diffraction orders. ©2015 Optical Society of America.
Open Access
Asymmetric transmission of linearly polarized waves and polarization angle dependent wave rotation using a chiral metamaterial
(Optical Society of America, 2011-07-18) Mutlu, M.; Akosman, A. E.; Serebryannikov, A. E.; Özbay, Ekmel
An electrically thin chiral metamaterial structure composed of four U-shaped split ring resonator pairs is utilized in order to realize polarization rotation that is dependent on the polarization of the incident wave at 6.2 GHz. The structure is optimized such that a plane wave that is linearly polarized at an arbitrary angle is an eigenwave of the system at this frequency. The analytical relation between the incident polarization and the polarization rotation is derived using transmission matrices. Furthermore, the proposed structure exhibits an asymmetric transmission of linearly polarized waves at 6.2 GHz. Plane waves traveling in opposite but perpendicular directions to the material plane are rotated by different angles. On the other hand, four incident polarization angles have been found for the same structure, at which the transmission is symmetric. The experiment results are in good agreement with the numerical results. (C)2011 Optical Society of America
Open Access
Asymmetric transmission of terahertz waves using polar dielectrics
(Optical Society of America, 2014-02-10) Serebryannikov, A. E.; Özbay, Ekmel; Nojima, S.
Asymmetric wave transmission is a Lorentz reciprocal phenomenon, which can appear in the structures with broken symmetry. It may enable high forward-to-backward transmittance contrast, while transmission for one of the two opposite incidence directions is blocked. In this paper, it is demonstrated that ultrawideband, high-contrast asymmetric wave transmission can be obtained at terahertz frequencies in the topologically simple, i.e., one- or two-layer nonsymmetric gratings, which are entirely or partially made of a polar dielectric working in the ultralow-epsilon regime inspired by phonon-photon coupling. A variety of polar dielectrics with different characteristics can be used that gives one a big freedom concerning design. Simple criteria for estimating possible usefulness of a certain polar dielectric are suggested. Contrasts exceeding 80dB can be easily achieved without a special parameter adjustment. Stacking a high-e corrugated layer with a noncorrugated layer made of a polar dielectric, one can enhance transmission in the unidirectional regime. At large and intermediate angles of incidence, a better performance can be obtained owing to the common effect of nonsymmetric diffractions and directional selectivity, which is connected with the dispersion of the ultralow-e material. At normal incidence, strong asymmetry in transmission may occur in the studied structures as a purely diffraction effect. (C) 2014 Optical Society of America
Open Access
Coupling effect between two adjacent chiral structure layers
(Optical Society of America, 2010-03-01) Li, Z.; Caglayan, H.; Colak, E.; Zhou, J.; Soukoulis, C. M.; Özbay, Ekmel
A pair of mutually twisted metallic cross-wires can produce giant optical activity. When this single chiral layer is stacked layer by layer in order to build a thick chiral metamaterial, strong coupling effects are found between the two adjacent chiral layers. We studied these coupling effects numerically and experimentally. The results show that the existing coupling between chiral layers can make the chiral properties of a two-layered chiral metamaterial different from the constituting single chiral layers. It is explained qualitatively that the coupling effects are generated from the coupling of metallic cross-wires belonging to different chiral layers. Our experimental results are in good agreement with the simulation results. ©2010 Optical Society of America
Open Access
Development of left-handed composite materials and negative refracting photonic crystals with subwavelength focusing
(SPIE, 2005) Özbay, Ekmel
We review the studies conducted in our group concerning electromagnetic properties of metamaterials and photonic crystals with negative effective index of refraction. In particular, we demonstate the true left handed behavior of a 2D composite metamaterial, by analyzing the electric and magnetic response of the material components systematically. The negative refraction, subwavelength focusing, and flat lens phenomena using 2D dielectric photonic crystals are also presented.
Open Access
EU NoE metamorphose: Metamaterials research activities
(SPIE, 2005) Özbay, Ekmel
We will present the activities of METAMORPHOSE a network of excellence (NoE) formed under EU-FP6 on the area of metamaterials. The main scientific objective of the partners of this consortium is to develop new types of artificial materials, referred to below as metamaterials, with electromagnetic properties that cannot be found among natural materials. The results of this development should lead to a conceptually new range of radio, microwave, and optical technologies, based on revolutionary new materials made by large-scale assembly of some basic elements (nanoscopic and microscopic) in unprecedented combinations. Further information on this NoE can be found in http://www.metamaterials-eu.org.
Open Access
Experimental study of subwavelength focusing by lefthanded metamaterials with a negative refractive index
(2007) Özbay, Ekmel; Aydin, K.
Two dimensional (2D) left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging are studied experimentally. A left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are simultaneously negative. 2D LHM structure is verified to have a negative refractive index by measuring the refraction through a prism-shaped sample. Subwavelength focusing is observed by using a flat LHM superlens.
Open Access
Highly directive radiation and negative refraction using photonic crystals
(Institute of Physics Publishing, 2005) Özbay, Ekmel; Bulu, I.; Aydin, K.; Caglayan H.; Alici, K. B.; Guven, K.
In this article, we present an experimental and numerical study of certain optical properties of two-dimensional dielectric photonic crystals (PCs). By modifying the band structure of a two-dimensional photonic crystal through its crystal parameters, we show how it is possible to confine the angular distribution of radiation from an embedded omnidirectional source. We then demonstrate that the anomalous band dispersions of PCs give rise to completely novel optical phenomena, in particular, the negative refraction of electromagnetic waves at the interface of a PC. We investigate the spectral negative refraction, which utilizes a transverse magnetic (TM)-polarized upper band of a PC, in detail and show that a high degree of isotropy can be achieved for the corresponding effective index of refraction. The presence of nearly a isotropic negative refractive index leads to focusing of omnidirectional sources by a PC slab lens, which can surpass certain limitations of conventional (positive refractive) lenses. These examples indicate the potential of PCs for photonics applications utilizing the band structure.
Open Access
Hybrid plasmon-phonon polariton bands in graphene-hexagonal boron nitride metamaterials [Invited]
(Optical Society of America, 2017) Hajian, H.; Ghobadi, A.; Dereshgi, S. A.; Butun, B.; Özbay, Ekmel
We theoretically investigate mid-infrared electromagnetic wave propagation in multilayered graphene-hexagonal boron nitride (hBN) metamaterials. Hexagonal boron nitride is a natural hyperbolic material that supports highly dispersive phonon polariton modes in two Reststrahlen bands with different types of hyperbolicity. Due to the hybridization of surface plasmon polaritons of graphene and hyperbolic phonon polaritons of hBN, each isolated unit cell of the graphene-hBN metamaterial supports hybrid plasmon-phonon polaritons (HPPs). Through the investigation of band structure of the metamaterial we find that, due to the coupling between the HPPs supported by each unit cell, the graphene-hBN metamaterial can support HPP bands. The dispersion of these bands can be noticeably modified for different thicknesses of hBN layers, leading to the appearance of bands with considerably flat dispersions. Moreover, analysis of light transmission through the metamaterial reveals that this system is capable of supporting high-k propagating HPPs. This characteristic makes graphene-hBN metamaterials very promising candidates for the modification of the spontaneous emission of a quantum emitter, hyperlensing, negative refraction, and waveguiding. © 2017 Optical Society of America.
Open Access
The magical world of metamaterials
(IEEE, 2009-10) Özbay, Ekmel
In recent years, there has been a burgeoning interest in rapidly growing field of metamaterials due to their unprecedented properties unattainable from ordinary materials. Veselago pointed out that a material exhibiting negative values of dielectric permittivity (ε) and magnetic permeability (μ) would have a negative refractive index [1]. Generally speaking, the dielectric permittivity (ε) and the magnetic permeability (μ) are both positive for natural materials. In fact it is possible to obtain negative values for ε and μ by utilizing proper designs of metamaterials. Left-handed electromagnetism and negative refraction are achievable with artificially structured metamaterials exhibiting negative values of permittivity and permeability simultaneously at a certain frequency region. The first steps to realize these novel type of materials were taken by Smith et al., where they were able to observe a left-handed propagation band at frequencies where both dielectric permittivity and magnetic permeability of the composite metamaterial are negative [2]. Soon after, left-handed metamaterials with an effective negative index of refraction are successfully demonstrated by various groups [3].
Open Access
Negative refraction and focusing by a left-handed material slab in free space
(IEEE, 2006) Aydın, Koray; Özbay, Ekmel
Negative refraction and focusing by a left-handed metamaterial (LHM) slab are experimentally verified. We measured refractive index of slab as -1.86. The flat lens behavior of LHM is demonstrated for two different point source distances. © 2006 Optical Society of America.
Open Access
Negative refraction and subwavelength focusing using left-handed composite metamaterials
(SPIE, 2008-01) Özbay, Ekmel; Aydın, Koray
We review experimental studies performed on left-handed metamaterials (LHM) at microwave frequencies. The metamaterial structure is composed of periodic arrays of split-ring resonators and wire meshes and exhibits a left-handed propagation band at frequencies of negative permittivity and negative permeability. Negative refraction is verified using prism shaped LHM and also by beam-shifting method. Subwavelength focusing of a point source is achieved with a resolution of 0.13λ, through a flat LHM superlens.
Open Access
Negative refraction by photonic crystals
(Nature, 2003) Cubukcu, E.; Aydin, K.; Özbay, Ekmel; Foteinopoulou, S.; Soukoulis, C. M.
Open Access
Observation of negative refraction and focusing in two-dimensional photonic crystals
(Institute of Physics Publishing Ltd., 2006) Özbay, Ekmel; Bulu, M.; Guven, K.; Caglayan, H.; Aydin, K.
We experimentally and theoretically demonstrate the negative refraction and focusing of electromagnetic (EM) waves by twodimensional photonic crystal slabs at microwave frequencies. The negative refraction is observed both for transverse magnetic (TM) and transverse electric (TE) polarized incident EM waves. Gaussian beam shifting method is used to verify the negative refractive index. The Subwavelength imaging and flat lens behavior of photonic crystals are succesfully demonstrated. We have been able to overcome the diffraction limit and focus the EM waves to a spot size of 0.21λ. Metallodielectric photonic crystals are employed to increase the range of angle of incidence that results in negative refraction. Experimental results and theoretical calculations are in good agreement throughout the work. © 2006 The Japan Society of Applied Physics.
Open Access
Observation of negative refraction and negative phase velocity in true left-handed metamaterials
(IEEE, 2007) Özbay, Ekmel; Soukoulis, C.M.
We report a true left-handed (LH) behavior in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures. The magnetic resonance of the SRR structure is demonstrated by comparing the transmission spectra of SRRs with that of closed SRRs. We confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined left-handed transmission band with a peak value of -1.2 dB (-0.3 dB/cm) is obtained. We also report the transmission characteristics of a 2D composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement. The experimental results agree extremely well with the theoretical calculations. © 2006 EuMA.
Open Access
Physics and applications of photonic crystals
(Nanotechnology Research Center NANOTAM, 2004) Özbay, Ekmel; Bulu I.; Aydin, K.; Caglayan H.; Guven, K.
In this article, we investigate how the photonic band gaps and the variety of band dispersions of photonic crystals can be utilized for various applications and how they further give rise to completely novel optical phenomena. The enhancement of spontaneous emission through coupled cavity waveguides in a one-dimensional silicon nitride photonic microcrystal is investigated. We then present the highly directive radiation from sources embedded in two-dimensional photonic crystals. The manifestation of novel and intriguing optical properties of photonic crystals are exemplified experimentally by the negative refraction and the focusing of electromagnetic waves through a photonic crystal slab with subwavelength resolution. © 2004 Elsevier B.V. All rights reserved.
Open Access
Refraction and essay film: the case of Alexander Sokurov
(2017-01) Nasirov, Yasin
This thesis analyzes refraction in essay film. As a self-reflexive method, refraction deals with the self-critique of visual representation in essay film. In this thesis, I develop two different dimensions of post-aesthetics of essay film in the line of semio-ideological understanding. The first dimension, as a horizontal interstitial aesthetization of essay film, deals with cinematic parataxis and metalepsis, where I discuss Godardian constellation and Agnès Varda’s metaleptic narrative through Adorno’s negative dialectics and Benjaminian constellation. The second dimension of the post-aesthetics of essay film, as vertical interstice, deals with intermediality and refraction. As constituting to different layer of essayistic construction in the film, intermediality is discussed in Peter Greenaway and Harun Farocki, and refraction is discussed in the line of photographic and visual epistemology. The thesis finalizes with the discussion of Alexander Sokurov’s late refractive cinema (Russian Ark (2002) and Francofonia (2015)), through the horizontal and vertical understanding of essay film’s post-aeshetics.
Open Access
Sabit karasal mikrodalga LOS/NLOS radyo linklerin enterferans analizi
(IEEE, 2015-05) Göktaş, Polat; Topcu, Satılmış; Karaşan, Ezhan; Altıntaş, Ayhan
Bu çalışmada, NATO Band 3+ (1350-2690 MHz) ve NATO Band 4 (4400-5000 MHz) frekans bantlarında çalışan sabit karasal mikrodalga LOS (karasal görüş çizgisi)/ NLOS (ufuk ötesi) radyo linkleri için enterferans modellenmesi ele alınmıştır. Sabit karasal noktadan-noktaya haberleşme sistemlerinde enterferansa maruz kalan istasyonlardaki hem açık havadaki hem de yağmurdaki saçılmadan kaynaklanan enterferansın hesaplanması yapılmıştır. Ayrıca, ITU-R P.452 Tavsiyesinde bahsedilen açık havadaki enterferans kaybının hesabındaki enterferans yayılım mekanizmaları incelenmiştir. Enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların koordinat bilgileri, enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların antenlerinin yerden yükseklikleri, anten ayrımcılıgı, ˘ polarizasyon tipi, radyo kırılma indeksi, deniz seviyesinden ortalama kırıcılık, zaman yüzdesi, yığın kategorisi, sayısal arazi yükseklik haritası ve iklimsel veriler gibi enterferans yayılım parametreleri kullanılarak çeşitli mikrodalga radyo linkler için enterferans analizleri yapılmıştır.
Open Access
Transmission spectra and the effective parameters for planar metamaterials with omega shaped metallic inclusions
(Elsevier, 2010) Li, Z.; Aydin, K.; Özbay, Ekmel
Planar metamaterials with omega shaped metallic inclusions were studied experimentally and theoretically. Our results show that when the incidence is perpendicular to the plane of the omega structure, the omega medium acts effectively as an electric resonator metamaterial. The stop band of the omega medium is due to the negative part of the electric resonance of the omega structure. The transmission band of the composite metamaterial (CMM) that is based on the omega medium is due to the strong positive part of the electric resonance of the omega structure. Consequently, the transmission band of the CMM does not coincide with the stop band of the omega medium. Furthermore, the transmission band of the CMM is a band with positive refractive indices. Our experimental and numerical results are in good agreement.