Browsing by Subject "Photonic band gap"
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Item Open Access All-chalcogenide glass omnidirectional photonic band gap variable infrared filters(AIP Publishing, 2009) Kondakci, H. E.; Yaman, M.; Koylu, O.; Dana, A.; Bayındır, MehmetWe report on the design, fabrication, and characterization of spatially variable infrared photonic band gap filter that consists of thermally evaporated, high refractive indexcontrast, amorphous chalcogenide glass multilayers. Due to graded thickness structure, the filter exhibits a position dependent stop band and a cavity mode ranging from 1.8 to 3.4 μm3.4 μmwavelengths. Reflection measurements on the variable filter agree well with theoretical calculations. These results pave the way to low-loss infrared mirrors, filters, spectral imaging, and miniaturized spectrometers at infrared region.Item Open Access All-chalcogenide variable infrared filter(SPIE, 2009) Kondakcı, H. Esat; Köyle, Özlem; Yaman, Mecit; Dana, Aykutlu; Bayındır, MehmetWe present the design, fabrication, characterization of spatially variable infrared filter and a demonstration of the filter as a simple infrared spectrometer. A varying photonic band gap filter which consists of thermally evaporated, high refractive index contrast amorphous chalcogenide glass multilayers, makes the structure suitable to be used as spectrometer. Due to graded thickness structure, the filter exhibits a position dependent stop band and a cavity mode ranging from 2 to 8 μm wavelengths. It is demonstrated that the filter can be used to detect absorption peaks of common gases in the cavity mode range of the filter. © 2009 SPIE.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 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.Item 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.Item Open Access Photonic band gap in the triangular lattice of Bose-Einstein-condensate vortices(2007) Taşgin, M. E.; Müstecaplioǧlu Ö. E.; Oktel, M. Ö.We investigate the photonic bands of an atomic Bose-Einstein condensate with a triangular vortex lattice. Index contrast between the vortex cores and the bulk of the condensate is achieved through the enhancement of the index via atomic coherence. The frequency-dependent dielectric function is used in the calculations of the bands, resulting in photonic band gap widths of a few megahertz. © 2007 The American Physical Society.Item Open Access Photonic band gap via quantum coherence in vortex lattices of Bose-Einstein condensates(The American Physical Society, 2005) Müstecaplioǧlu, O. E.; Oktel, M. Ö.We investigate the optical response of an atomic Bose-Einstein condensate with a vortex lattice. We find that it is possible for the vortex lattice to act as a photonic crystal and create photonic band gaps, by enhancing the refractive index of the condensate via a quantum coherent scheme. If high enough index contrast between the vortex core and the atomic sample is achieved, a photonic band gap arises depending on the healing length and the lattice spacing. A wide range of experimentally accessible parameters are examined and band gaps in the visible region of the electromagnetic spectrum are found. We also show how directional band gaps can be used to directly measure the rotation frequency of the condensate.Item Open Access Slow surface plasmons on Moiré surfaces(IEEE, 2009) Şenlik, S. Seçkin; Kocabaş, A.; Aydınlı, AtillaIn this report, the authors present the design, fabrication and realization of coupled plasmonic cavities using metallic Moire structures. The phase shifts at the nodes of Moire pattern enable localization of SPPs resulting in a mini band in the band gap region. The authors find group velocities around V g =0.44c at the center of the mini band and approaches to zero at the edges of mini band.Item Open Access Two-dimensional ferroelectric photonic crystals: Optics and band structure(Taylor & Francis Inc., 2013-09-20) Simsek S.; Mamedov, A. M.; Özbay, EkmelIn this report we present an investigation of the optical properties and band structure calculations for the photonic structures based on the functional materials- ferroelectrics. A theoretical approach to the optical properties of the 2D and 3D photonic crystals which yields further insight in the phenomenon of the reflection from different families of lattice planes in relation to the presence of photonic gaps or photonic bands. We calculate the photonic bands and optical properties of LiNbO3 based photonic crystals. Calculations of reflection and transmission spectra show the features correspond to the onset of diffraction, as well as to additional reflectance structures at large values of the angle of incidence. © 2013 Copyright Taylor and Francis Group, LLC.Item Open Access Vortex lattice of a Bose-Einstein condensate as a photonic band gap material(IOP Institute of Physics Publishing, 2009) Taşgin, M. E.; Müstecaplioǧlu, Ö. E.; Oktel, M. Ö.Photonic crystal behavior of a rotating Bose-Einstein condensate with a triangular vortex lattice is reviewed and a scheme for getting much wider band gaps is proposed. It is shown that photonic band gaps can be widened an order of magnitude more by using a Raman scheme of index enhancement, in comparison to previously considered upper level microwave scheme.