Browsing by Author "Soukoulis, C. M."

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Open Access
Bilayer metamaterial: analysis of left-handed transmission and retrieval of effective medium parameters
(Institute of Physics Publishing Ltd., 2007) Guven, K.; Cakmak, A. O.; Caliskan, M. D.; Gundogdu, T. F.; Kafesaki, M.; Soukoulis, C. M.; Özbay, Ekmel
We report an experimental and numerical analysis of a planar metamaterial designed for normal-to-plane propagation, and operating at microwave frequencies. The metamaterial consists of cutwire and wire patterns, which are arranged periodically on both sides of a dielectric layer, in the form of a bilayer. The left-handed transmission band of the metamaterial is demonstrated experimentally. The effective index of refraction retrieved from the S parameters is found to be negative within this transmission band. An independent negative refraction experiment supports the existence of the negative index of refraction for the metamaterial.
Open Access
Broadband mixing of PT-symmetric and PT-broken phases in photonic heterostructures with a one-dimensional loss/gain bilayer
(Nature Publishing Group, 2017) Özgün E.; Serebryannikov, A. E.; Özbay, Ekmel; Soukoulis, C. M.
Combining loss and gain components in one photonic heterostructure opens a new route to efficient manipulation by radiation, transmission, absorption, and scattering of electromagnetic waves. Therefore, loss/gain structures enabling PT-symmetric and PT-broken phases for eigenvalues have extensively been studied in the last decade. In particular, translation from one phase to another, which occurs at the critical point in the two-channel structures with one-dimensional loss/gain components, is often associated with one-way transmission. In this report, broadband mixing of the PT-symmetric and PT-broken phases for eigenvalues is theoretically demonstrated in heterostructures with four channels obtained by combining a one-dimensional loss/gain bilayer and one or two thin polarization-converting components (PCCs). The broadband phase mixing in the four-channel case is expected to yield advanced transmission and absorption regimes. Various configurations are analyzed, which are distinguished in symmetry properties and polarization conversion regime of PCCs. The conditions necessary for phase mixing are discussed. The simplest two-component configurations with broadband mixing are found, as well as the more complex three-component configurations wherein symmetric and broken sets are not yet mixed and appear in the neighbouring frequency ranges. Peculiarities of eigenvalue behaviour are considered for different permittivity ranges of loss/gain medium, i.e., from epsilon-near-zero to highepsilon regime. © 2017 The Author(s).
Open Access
Chiral metamaterials with negative refractive index based on four "U" split ring resonators
(American Institute of Physics, 2010-08-23) Li, Z.; Zhao, R.; Koschny, T.; Kafesaki, M.; Alici, K. B.; Colak, E.; Caglayan, H.; Özbay, Ekmel; Soukoulis, C. M.
A uniaxial chiral metamaterial is constructed by double-layered four "U" split ring resonators mutually twisted by 90°. It shows a giant optical activity and circular dichroism. The retrieval results reveal that a negative refractive index is realized for circularly polarized waves due to the large chirality. The experimental results are in good agreement with the numerical results.
Open Access
Compact planar far-field superlens based on anisotropic left-handed metamaterials
(American Physical Society, 2009-09-15) Shen, N.-H.; Foteinopoulou, S.; Kafesaki, M.; Koschny, T.; Özbay, Ekmel; Economou, E. N.; Soukoulis, C. M.
Pendry’s perfect lens has spurred intense interest for its practical realization at visible frequencies. However, fabrication of low-loss isotropic left-handed metamaterials is a current challenge. In this work, we theoretically show that under specific conditions anisotropic metamaterial slabs can emulate Pendry’s perfect-lens phenomenon on a plane. Geometric optics leads to a new lens formula for this special anisotropic metamaterial superlens, which allows significant shrinkage of the metamaterial slab thickness for a certain range of far-field operation. Conversely, such anisotropic metamaterial superlens with the same thickness as its isotropic analog can operate for much larger distances between object and lens. We present numerical simulations which confirm our theoretical calculations. In particular, we find subdiffraction focusing that rivals the perfect isotropic negative-index metamaterial lens performance and obeys the new lens formula as predicted. In addition, we demonstrate that it is possible to attain far-field superfocusing with a metamaterial slab as thin as half the free-space wavelength. We believe this work will inspire new anisotropic metamaterial designs and opens a promising route for the realization of compact far-field superlenses in the visible regime.
Open Access
Composite chiral metamaterials with negative refractive index and high values of the figure of merit
(Optical Society of America, 2012) Li, Z.; Caglayan, H.; Alici, K. B.; Kafesaki, M.; Soukoulis, C. M.; Özbay, Ekmel
A composite chiral metamaterial (CCMM) is designed and studied both numerically and experimentally. The CCMM is constructed by the combination of a continuous metallic wires structure and a purely chiral metamaterial (CMM) that consists of conjugated Rosettes. For the CMM, only very small, useful bands of negative index can be obtained for circularly polarized waves. These bands are all above the chiral resonance frequencies because of the high value of the effective parameter of relative permittivity epsilon. After the addition of the continuous metallic wires, which provide negative permittivity, the high value of epsilon can be partially compensated. Thus, a negative index band for the left circularly polarized wave that is below the chiral resonance frequency is obtained for the CCMM. At the same time, a negative index band for the right circularly polarized wave that is above the chiral resonance frequency is also obtained. Furthermore, both negative index bands correspond to the transmission peaks and have high values of the figure of merit. Therefore, the CCMM design that is proposed here is more suitable than the CMM for the construction of chiral metamaterials with a negative index. (C) 2012 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
Defect structures in a layer-by-layer photonic band-gap crystal
(American Physical Society, 1995) Özbay, Ekmel; Tuttle, G.; Sigalas, M.; Soukoulis, C. M.; Ho, K. M.
We have experimentally and theoretically investigated defect structures that are incorporated into a three-dimensional layer-by-layer photonic band-gap crystal. The defects are formed by either adding or removing dielectric material to or from the crystal. For both cases, we observed localized modes with frequencies that lie within the forbidden band gap of the pure crystal. Relatively high peak transmission (10 dB below the incident signal), and high quality factors (2000) have been measured. These measurements were in good agreement with theoretical simulations. Theoretical calculations also predict very high (Q>106) quality factors for certain cavity structures. © 1995 The American Physical Society.
Open Access
Defect structures in metallic photonic crystals
(A I P Publishing LLC, 1996-12-16) Özbay, Ekmel; Temelkuran, B.; Sigalas, M.; Tuttle, G.; Soukoulis, C. M.; Ho, K. M.
We have investigated metallic photonic crystals built around a layer‐by‐layer geometry. Two different crystal structures (face‐centered‐tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations.
Open Access
Effect of disorder on magnetic resonance band gap of split-ring resonator structures
(Optical Society of American (OSA), 2004) Aydın, K.; Güven, K.; Katsarakis, N.; Soukoulis, C. M.; Özbay, Ekmel
We investigated the influence of periodicity, misalignment, and disorder on the magnetic resonance gap of split-ring resonators (SRRs) which are essential components of left handed-metamaterials (LHMs). The resonance of a single SRR which is induced by the split is experimentally demonstrated by comparing transmission spectra of SRR and closed ring resonator. Misaligning the SRR boards do not affect the magnetic resonance gap, while destroying the periodicity results in a narrower band gap. The disorder in SRR layers cause narrower left-handed pass band and decrease the transmission level of composite metamaterials (CMMs), which may significantly affect the performance of these LHMs. © 2004 Optical Society of America.
Open Access
Experimental demonstration of a left-handed metamaterial operating at 100 GHz
(American Physical Society, 2006) Gökkavas, M.; Güven, K.; Bulu, I.; Aydın, K.; Penciu, R. S.; Kafesaki, M.; Soukoulis, C. M.; Özbay, Ekmel
The existence of a left-handed (LH) transmission band in a bulk composite metamaterial (CMM) around 100 GHz is demonstrated experimentally. The CMM consists of stacked planar glass layers on which periodic patterns of micron-scale metallic wires and split-ring resonators are fabricated. The LH nature of the CMM band is proved by comparing the transmission spectra of individual CMM components. Theoretical investigation of the CMM by transmission simulations and an inversion scheme for the retrieval of the effective permeability and permittivity functions supports the existence of LH behavior. © 2006 The American Physical Society.
Open Access
Experimental demonstration of highly confined photonic crystal based waveguides
(IEEE, 2001) Bayındır, Mehmet; Özbay, Ekmel; Temelkuran, B.; Sigalas, M. M.; Soukoulis, C. M.; Biswas, R.; Ho, K. M.
The bending and guiding of the electromagnetic (EM) waves in highly confined waveguides was demonstrated. The electromagnetic waves were constructed by removing a single rod from a perfect three layer-by-layer photonic crystals. A layer-by-layer dielectric photonic crystal based on square shaped alumina rods was used with center-to-center separation of 1.12 cm. The results suggested the use of the layer-by-layer photonic crystal structure in the design of optoelectronic integrated circuits.
Open Access
Experimental observasion of true left-handed transmission peaks in metamaterials
(Optical Society of America, 2004-11-15) Aydin, K.; Guven, K.; Kafesaki, M.; Zhang, L.; Soukoulis, C. M.; Özbay, Ekmel
We report true left-handed (LH) behavior in a composite metamaterial consisting of a periodically arranged split ring resonator (SRR) and wire structures. We demonstrate the magnetic resonance of the SRR structure by comparing the transmission spectra of SRRs with those of closed SRRs. We have 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 LH transmission band with a peak value of -1.2 dB (-0.3 dB/cm) was obtained. The experimental results agree extremely well with the theoretical calculations. (C) 2004 Optical Society of America.
Open Access
Guiding, bending, and splitting of electromagnetic waves in highly confined photonic crystal waveguides
(American Physical Society, 2001) Bayındır, Mehmet; Özbay, Ekmel; Temelkuran, B.; Sigalas, M. M.; Soukoulis, C. M.; Biswas, R.; Ho, K. M.
We have experimentally demonstrated the guiding, bending, and splitting of electromagnetic (EM) waves in highly confined waveguides built around three-dimensional layer-by-layer photonic crystals by removing a single rod. Full transmission of the EM waves was observed for straight and bended waveguides. We also investigated the power splitter structures in which the input EM power could be efficiently divided into the output waveguide ports. The experimental results, dispersion relation and photon lifetime, were analyzed with a theory based on the tight-binding photon picture. Our results provide an important tool for designing photonic crystal based optoelectronic components.
Open Access
Investigation of magnetic resonances for different split-ring resonator parameters and designs
(Institute of Physics Publishing, 2005) Aydin, K.; Bulu, I.; Guven, K.; Kafesaki, M.; Soukoulis, C. M.; Özbay, Ekmel
We investigate the magnetic resonance of split-ring resonators (SRR) experimentally and numerically. The dependence of the geometrical parameters on the magnetic resonance frequency of SRR is studied. We further investigate the effect of lumped capacitors integrated to the SRR on the magnetic resonance frequency for tunable SRR designs. Different resonator structures are shown to exhibit magnetic resonances at various frequencies depending on the number of rings and splits used in the resonators.
Open Access
Laser-micromachined millimeter-wave photonic band-gap cavity structures
(American Institute of Physics, 1995) Özbay, Ekmel; Tuttle, G.; McCalmont, J. S.; Sigalas, M.; Biswas, R.; Soukoulis, C. M.; Ho, K. M.
We have used laser-micromachined alumina substrates to build a three-dimensional photonic band-gap crystal. The rod-based structure has a three-dimensional full photonic band gap between 90 and 100 GHz. The high resistivity of alumina results in a typical attenuation rate of 15 dB per unit cell within the band gap. By removing material, we have built defects which can be used as millimeter-wave cavity structures. The resulting quality ~Q! factors of the millimeter-wave cavity structures were as high as 1000 with a peak transmission of 10 dB below the incident signal. © 1995 American Institute of Physics.
Open Access
Left-and right-handed transmission peaks near the magnetic resonance frequency in composite metamaterials
(American Physical Society, 2004) Katsarakis, N.; Koschny, T.; Kafesaki, M.; Economou, E. N.; Özbay, Ekmel; Soukoulis, C. M.
We present free-space microwave measurements on composite metamaterials (CMMs) consisting of split ring resonators (SRRs) and wires either on the same dielectric board or on alternating boards. Our experimental results disprove the widely held belief that the occurrence of a CMM transmission peak within the stop bands of the SRRs alone and wires alone constitutes a clear demonstration of left-handed (LH) behavior. This belief is based on the assumption that the stop bands of SRRs alone and wires alone are not affected by the simultaneous presence of both. We show here that this assumption is wrong: The effective plasma frequency, ω′p, of the CMM is actually substantially lower than the wires-only plasma frequency, ωp; furthermore, the in-plane wires, as opposed to the off-plane case, push the magnetic resonance frequency of the SRRs, ωm, to a higher value, ω′m, for the CMM. We conclude that the criterion for deciding whether a peak in the transmission spectrum through a CMM is really left-handed is for the peak to be located above ω′m and below ω′p. Our results provide a definite way for experimentally identifying ω′p.
Open Access
Negative refraction and superlens behavior in a two-dimensional photonic crystal
(American Physical Society, 2005) Moussa, R.; Foteinopoulou, S.; Zhang, L.; Tuttle, G.; Guven, K.; Özbay, Ekmel; Soukoulis, C. M.
We experimentally and theoretically studied a left-handed structure based on a photonic crystal (PC) with a negative refractive index. The structure consists of triangular array of rectangular dielectric bars with dielectric constant 9.61. Experimental and theoretical results demonstrate the negative refraction and the superlensing phenomena in the microwave regime. The results show high transmission for our structure for a wide range of incident angles. Furthermore, surface termination within a specific cut of the structure excite surface waves at the interface between air and PC and allow the reconstruction of evanescent waves for a better focus and better transmission. The normalized average field intensity calculated in both the source and image planes shows almost the same full width at half maximum for the source and the focused beam.
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 negative phase velocity in left-handed metamaterials
(American Institute of Physics, 2005) Aydin, K.; Guven, K.; Soukoulis, C. M.; Özbay, Ekmel
We report the transmission characteristics of a two-dimensional (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.
Open Access
Optically implemented broadband blueshift switch in the terahertz regime
(American Physical Society, 2011-01-18) Shen, N. H.; Massaouti, M.; Gokkavas, M.; Manceau J. M.; Özbay, Ekmel; Kafesaki, M.; Koschny, T.; Tzortzakis, S.; Soukoulis, C. M.
We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime.