Browsing by Subject "Light transmission"
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Item Open Access Asymmetric light propagation in chirped photonic crystal waveguides(Optical Society of American (OSA), 2012) Kurt H.; Yilmaz, D.; Akosman, A.E.; Özbay, EkmelWe 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 transmission characteristics of this structure reveals optical diode like transmission behavior. The amount of power collected at the output of the waveguide centerline is different for the forward and backward propagation directions in the designed configuration. The advantageous properties of the proposed approach are the linear optic concept, compact configuration and compatibility with the integrated photonics. These features are expected to hold great potential for implementing practical optical rectifier-type devices. © 2012 Optical Society of America.Item Open Access Band gap and optical transmission in the Fibonacci type one-dimensional A5B6C7 based photonic crystals(Wiley-VCH Verlag, 2015) Simsek S.; Koc, H.; Palaz S.; Oltulu, O.; Mamedov, A. M.; Özbay, EkmelIn this work, we present an investigation of the optical properties and band structure calculations for the photonic crystal structures (PCs) based on one-dimensional (1D) photonic crystal. Here we use 1D A5B6C7(A:Sb; B:S,Se; C:I) based layers in air background. We have theoretically calculated photonic band structure and optical properties of A5B6C7(A:Sb; B:S,Se; C:I) based PCs. In our simulation, we employed the finite-difference time domain (FDTD) technique and the plane wave expansion method (PWE) which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access Band-dropping via coupled photonic crystal waveguides(Optical Society of American (OSA), 2002) Bayındır, Mehmet; Özbay, EkmelWe observe the dropping of electromagnetic waves having a specific frequency or a certain frequency band in two-dimensional dielectric photonic crystals. The single frequency is dropped via cavity-waveguide coupling. Tunability of the demultiplexing mode can be achieved by modifying the cavity properties. The band-dropping phenomenon is achieved by introducing interaction between an input planar, or coupled-cavity, waveguide and the output coupled-cavity waveguides (CCWs). The dropping band can be tuned by changing the coupling strength between the localized cavity modes of the output CCWs. We also calculate the transmission spectra and the field patterns by using the finite-difference-time-domain (FDTD) method. Calculated results agree well with the microwave measurements. © 2002 Optical Society of America.Item Open Access Coupled-cavity structures in photonic crystals(Materials Research Society, 2002) Bayındır, Mehmet; Özbay, EkmelWe investigate the localized coupled-cavity modes in two-dimensional dielectric photonic crystals. The transmission, phase, and delay time characteristics of the various coupled-cavity structures are measured and calculated. We observed waveguiding through the coupled cavities, splitting of electromagnetic waves in waveguide ports, and switching effect in such structures. The corresponding field patterns and the transmission spectra are obtained from the finite-difference-time-domain (FDTD) simulations. We also develop a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation.Item 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, EkmelWe 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.Item Open Access Experimental demonstration of negative refraction and subwavelength imaging by left-handed composite metamaterials(Cambridge University Press, 2006) Özbay, Ekmel; Aydın, Koray; Özkan, Gonca; Bulu, İrfanWe report a true left-handed (LH) behavior and focusing 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 and the experimental results agree extremely well with the theoretical calculations. By measuring the refracted electromagnetic (EM) waves from a LHM slab, we found an effective refractive index of -1.86. A 2D scanning transmission measurement technique was used to measure the intensity distribution of the electromagnetic (EM) waves that radiate from the point source. The flat lens behavior of a 2D CMM slab was demonstrated for two different point source distances of ds = 0.5λ and λ. The full width at half maximum of the focused beams is 0.36λ and 0.4λ, respectively, which are both below the diffraction limit. © 2006 Materials Research Society.Item Open Access Experimental observation of left-handed transmission in a bilayer metamaterial under normal-to-plane propagation(Optical Society of American (OSA), 2006) Guven, K.; Caliskan, M.D.; Özbay, EkmelWe demonstrate experimentally the double-negative (ε < 0, μ < 0) transmission band of a one-dimensional metamaterial structure under normal-to-plane propagation in the microwave regime. The structure consists of stacked bilayers of metal cutwire and wire pairs, which are separated by a thin dielectric layer. The existence of the negative index of refraction is inferred from the transmission and phase spectra obtained by using multilayer metamaterial samples. Another metamaterial structure incorporating non-magnetic (electrically shorted) cutwire pairs does not exhibit the corresponding transmission band, which supports the true lefthanded behavior of the metamaterial. © 2006 Optical Society of America.Item Open Access Extracting power from sub-wavelength apertures by using electrically small resonators: Phenomenology, modeling, and applications(IEEE, 2012) Bilotti F.; Di Palma L.; Ramaccia, D.; Toscano, A.; Vegni L.; Ateş, Damla; Özbay, EkmelIn this contribution, we review our recent work on the extraction of the electromagnetic power from electrically small apertures by using metamaterial-inspired resonators. First, we present an antenna interpretation of the power transmission through sub-wavelength apertures and discuss the questioned concept of 'enhanced transmission'. Then, we present the so-called 'connected bi-omega particle' and the related analytical model. After that, exploiting proper numerical and experimental examples, we also show that the electromagnetic response of such a particle is not influenced by the surrounding environment. This unique property makes the particle a suitable candidate for the implementation of microwave components based on the selective power extraction from electrically small apertures. Finally, the application of the proposed concepts to the design of innovative microwave components, such as waveguide filters, diplexers, power-splitters, modal filters, horn antennas, etc. will be considered and demonstrated through proper numerical and experimental results. © 2012 IEEE.Item Open Access Fabry-Perot-type resonances in metallic photonic crystals(IEEE, 1998) Serpengüzel, Ali; Savran, KerimA metallic photonic crystals (MPC) with a face-centered cubic (FCC) Bravais lattice is investigated in the microwave regime. It was found that the transmission below and above the stop band is unity, which is quite remarkable since the metallic surface would have reflected 99.97% of the incident radiation in the given microwave frequency range. The effect of the incidence angle on the transmission of the MPC was also studied.Item 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, EkmelWe 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.Item Open Access Investigation of AlGaN buffer layers on sapphire grown by MOVPE(SPIE, 2004) Van Gemmern, P.; Dikme, Y.; Bıyıklı, Necmi; Kalisch, H.; Özbay, Ekmel; Jansen, R. H.; Heuken, M.In this work, AlGaN layers were grown on sapphire by metal-organic vapor phase epitaxy (MOVPE) on (0001)-oriented sapphire substrates, with the intention to investigate the effect of varying Al/MO and V/III ratios on the Al incorporation into the AlGaN layers. The parameters Al/MO and V/III describe the proportions of source material inside the reactor. With the help of optical transmission measurements, characteristic cut-off wavelengths of the Al xGa(1-x)N layers were determined. These wavelengths were used to calculate the Al content x of the layers, leading to values between 26.6% and 52.1%. Using the two process parameters Al/MO and V/III as input and the Al content of the AlGaN layers as a response variable, the experimental results were further investigated with the help of the software STATGRAPHICS. An estimated response surface for the variable x was generated. It was found that the Al incorporation is only tunable within a wide range for high V/III ratios of about 900. For constant Al/MO ratios and varying V/III ratios, two different growth characteristics were observed at high and low Al/MO values. This behavior is ascribed to the superposition of two oppositional effects.Item Open Access Kilometer-long ordered nanophotonic devices by preform-to-fiber fabrication(Institute of Electrical and Electronics Engineers, 2006) Bayındır, Mehmet; Abouraddy, A.F.; Shapira O.; Viens J.; Saygin-Hinczewski, D.; Sorin, F.; Arnold, J.; Joannopoulos, J. D.; Fink, Y.A preform-to-flber approach to the fabrication of functional fiber-based devices by thermal drawing in the viscous state is presented. A macroscopic preform rod containing metallic, semiconducting, and insulating constituents in a variety of geometries and close contact produces kilometer-long novel nanostructured fibers and fiber devices. We first review the material selection criteria and then describe metal-semiconductor-metal photosensitive and thermally sensitive fibers. These flexible, lightweight, and low-cost functional fibers may pave the way for new types of fiber sensors, such as thermal sensing fabrics, artificial skin, and large-area optoelectronic screens. Next, the preform-to-fiber approach is used to fabricate spectrally tunable photodetectors that integrate a photosensitive core and a nanostructured photonic crystal structure containing a resonant cavity. An integrated, self-monitoring optical-transmission waveguide is then described that incorporates optical transport and thermal monitoring. This fiber allows one to predict power-transmission failure, which is of paramount importance if high-power optical transmission fines are to be operated safely and reliably in medical, industrial and defense applications. A hybrid electron-photon fiber consisting of a hollow core (for optical transport by means of a photonic bandgap) and metallic wires (for electron transport) is described that may be used for transporting atoms and molecules by radiation pressure. Finally, a solid microstructured fiber fabricated with a highly nonlinear chalcogenide glass enables the generation of supercontinuum light at near-infrared wavelengths.Item Open Access Quantum correlated light pulses from sequential superradiance of a condensate(2009) Taşgin, M.E.; Oktel, M. Ö.; You L.; MüstecaplIoǧlu Ö.E.We discover an inherent mechanism for entanglement swap associated with sequential superradiance from an atomic Bose-Einstein condensate. Based on careful examinations with both analytical and numerical approaches, we conclude that as a result of the swap mechanism, Einstein-Podolsky-Rosen-type quantum correlations can be detected among the scattered light pulses. © 2009 The American Physical Society.Item Open Access Reflection properties and defect formation in metallic photonic crystals(IEEE, 1998-05) Özbay, Ekmel; Temelkuran, Burak; Sigalas, M.; Tuttle, G.; Soukoulis, C. M.; Ho, K. M.The reflection properties of layer-by-layer metallic photonic crystals were investigated using metallic photonic crystals with simple-tetragonal (st) structure. The observed properties were used to predict defect formation in these crystals. The reflection and transmission amplitude characteristics were measured by a network analyzer and standard gain horn antennas. Transformation matrix method was employed for the theoretical simulations.Item Open Access Resonant excitation of surface plasmons in one-dimensional metallic grating structures at microwave frequencies(Institute of Physics Publishing, 2005) Akarca-Biyikli, S. S.; Bulu, I.; Özbay, EkmelGrating-coupling phenomena between surface plasmons and electromagnetic waves were studied in the microwave spectrum using metallic gratings. Transmission measurements were carried out to observe the transmitted radiation around the surface plasmon resonance frequencies. Grating structures with subwavelength apertures were designed for transmission experiments. Measurements were made in the microwave spectrum of 10-37.5 GHz, corresponding to a wavelength region of 8-30 mm. The A1 samples had a grating periodicity of 16 mm. A 2 mm wide subwavelength slit was opened for transmission samples. Samples with one/double-sided gratings displayed remarkably enhanced transmission and directivity with respect to the reference sample without gratings. The experimental results agreed well with theoretical simulations. ∼50% transmission at 20.7 mm, ∼25-fold enhancement, and ±4° angular divergence were achieved with a ∼λ/10 aperture.Item Open Access Structural, optical and electrical characteristics BaSrTiOx thin films: Effect of deposition pressure and annealing(Elsevier BV * North-Holland, 2017) Bayrak, T.; Ozgit-Akgun, C.; Goldenberg, E.Among perovskite oxide materials, BaSrTiOx (BST) has attracted great attention due to its potential applications in oxide-based electronics. However, reliability and efficiency of BST thin films strongly depend on the precise knowledge of the film microstructure, as well as optical and electrical properties. In the present work, BST films were deposited at room temperature using radio frequency magnetron sputtering technique. The impact of deposition pressure, partial oxygen flow, and post-deposition annealing treatment on film microstructure, surface morphology, refractive index, and dielectric constants were studied by X-ray diffraction, scanning electron microscopy, spectrophotometry, ellipsometry, photoluminescence, as well as capacitance-voltage measurements. Well-adhered and uniform amorphous films were obtained at room temperature. For all as-deposited films, the average optical transmission was ~ 85% in the VIS-NIR spectrum. The refractive indices of BST films were in the range of 1.90–2.07 (λ = 550 nm). Post-deposition annealing at 800 °C for 1 h resulted in polycrystalline thin films with increased refractive indices and dielectric constants, however reduced optical transmission values. Frequency dependent dielectric constants were found to be in the range of 46–72. However, the observed leakage current was relatively small, about 1 μA. The highest FOM values were obtained for films deposited at 0.67 Pa pressures, while charge storage capacity values increased with increased deposition pressure. Results show that room-temperature grown BST films have potential for device applications.Item Open Access Ultrafast and highly efficient resonant cavity enhanced photodiodes(SPIE, 2003-09) Özbay, Ekmel; Kimukin, İbrahim; Bıyıklı, NecmiIn this talk, we will review our research efforts on resonant cavity enhanced (RCE) high-speed high-efficiency photodiodes (PDs) operating in the 1st and 3rd optical communication windows. Using a microwave compatible planar fabrication process, we have designed and fabricated GaAs and InGaAs based RCE photodiodes. For RCE GaAs Schottky type photodiodes, we have achieved peak quantum efficiencies of 50% and 75% with semi-transparent (Au) and transparent (indium-tin-oxide) Schottky layers respectively. Along with 3-dB bandwidths of 50 and 60 GHz, these devices exhibit bandwidth-efficiency (BWE) products of 25 GHz and 45 GHz respectively. By using a postprocess recess etch, we tuned the resonance wavelength of an RCE InGaAs PD from 1605 to 1558 nm while keeping the peak efficiencies above 60%. The maximum quantum efficiency was 66% at 1572 nm which was in good agreement with our theoretical calculations. The photodiode had a linear response up to 6 mW optical power, where we obtained 5 mA photocurrent at 3 V reverse bias. The photodetector had a temporal response of 16 psec at 7 V bias. After system response deconvolution, the 3-dB bandwidth of the device was 31 GHz, which corresponds to a bandwidth-efficiency product of 20 GHz.Item Open Access Unidirectional transmission in non-symmetric gratings containing metallic layers(Optical Society of American (OSA), 2009) Serebryannikov, A.E.; Özbay, EkmelThe mechanism of achieving unidirectional transmission in the gratings, which only contain isotropic dielectric and metallic layers, is suggested and numerically validated. It is shown that significant transmission in one direction and nearly zero transmission in the opposite direction can be obtained in the same intrinsically isotropic gratings as those studied recently in A. E. Serebryannikov and E. Ozbay, Opt. Express 17, 278 (2009), but at a non-zero angle of incidence. The tilting, non-symmetric features of the grating and the presence of a metallic layer with a small positive real part of the index of refraction are the conditions that are necessary for obtaining the unidirectionality. Single- and multibeam operational regimes are demonstrated. The frequency and angle ranges of the unidirectional transmission can be estimated by using the conventional framework based on isofrequency dispersion contours and construction lines that properly take into account the periodic features of the interfaces, but should then be corrected because of the tunneling arising within the adjacent ranges. After proper optimization, this mechanism is expected to become an alternative to that based on the use of anisotropic materials. © 2009 Optical Society of America.