Browsing by Subject "Photonic Crystals"

Now showing 1 - 8 of 8

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
Characterization of photonic crystals at microwave frequencies
(1996) Temelkuran, Burak
VVe investigated the surface reflection properties of layer-by-layer photonic crystals, for dielectric and metallic based photonic crystals. By using a FabryPerot cavity analogy with the reflection-phase information of the photonic crystals, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. The Fabry-Perot cavity analogy was also used to relate the quality factors of the planar defect structures to the transmission of the mirrors of the cavity. A simple model was used to simulate the transmission spectra of planar defect structures, which agreed well with the experimental data. We also investigated the transmission and reflection properties of two different metallic crystal structures (face-centeredtetragonal and simple tetragonal). We obtained rejection rates of 7-8 dB per layer from 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 of metallic structures. Planar defect structures built around metallic structures resulted in higher quality factors (2250). We observed high reflection-rejection ratios (-80 dB) at defect frequencies for planar defect structures, which was explained by using the Fabry-Perot analogy. Finally, the enhanced field inside the defect volume was measured, by using a monopole receiver antenna inserted inside the defect. The maximum observed enhancement with respect to the incident field was around 200 for a planar defect structure. By placing a Schottky diode detector inside planar and box-like defects, we built resonant cavity enhanced (RCE) detectors and measured the enhanced field inside the defect.
Open Access
Design of compact optical devices based on periodic meta-structures
(2013) Akosman, Ahmet Emin
Manipulation of the flow of light is demanded for several applications such as communication, data storage, sensor, photovoltaic cells, microscopy, lasers and light emitting diodes for the purpose of designing compact, high-throughput and high efficiency optical devices. Nevertheless, the control of the propagation of the light becomes much harder in devices with smaller geometries mostly because of diffractions, loss mechanisms and fabrication difficulties. Furthermore, materials that are already available in the nature do not provide unprecedented optical properties for nanoscale optical applications. Due to this fact that fabrication of artificial materials is needed for utilizing novel and intriguing optical devices. For this purpose, some relatively new research fields have emerged like photonic crystals, metamaterials and high contrast gratings. We propose several designs based on aforementioned meta-structures to achieve compact and practically realizable optical devices. We presented compact optical demultiplexer, diode-like device and electro-optic modulator designs that are based on photonic crystals. We also proposed two circular polarizer designs based on metamaterials and high contrast gratings. Further, we investigated unidirectional transmission and polarization manipulation properties in chiral metamaterials. For most of the proposed designs, we also experimentally verified the numerical and theoretical findings. In conclusion, we can claim that the utilization of artifically structured materials give opportunity to realize the control of light much more easily in nanoscale designs.
Open Access
Focusing of electromagnetic waves by a left-handed metamaterial flat lens
(Optical Society of America, 2005-10-31) Aydin, K.; Bulu, I.; Özbay, Ekmel
We present here the experimental results from research conducted on negative refraction and focusing by a two-dimensional (2D) left-handed metamaterial (LHM) slab. By measuring the refracted electromagnetic (EM) waves from a LHM slab, we find an effective refractive index of -1.86. A 2D scanning transmission measurement technique is used to measure the intensity distribution of the EM waves that radiate from the point source. The flat lens behavior of a 2D LHM slab is demonstrated for two different point source distances of ds = 0.5λ and λ. The full widths at half maximum of the focused beams are 0.36λ and 0.4λ, respectively, which are both below the diffraction limit. © 2005 Optical Society of America
Open Access
Hyperbolic metamaterials based on quantum-dot plasmon resonator nanocomposites
(Optical Society of America, 2014) Zhokovsky, S. V.; Ozel, T.; Mutlugun, E.; Gaponik, N.; Eychmuller, A.; Lavrinenko, A. V.; Demir, Hilmi Volkan; Gaponenko, S. V.
We theoretically demonstrate that nanocomposites made of colloidal semiconductor quantum dot monolayers placed between metal nanoparticle monolayers can function as multilayer hyperbolic metamaterials. Depending on the thickness of the spacer between the quantum dot and nanoparticle layers, the effective permittivity tensor of the nanocomposite is shown to become indefinite, resulting in increased photonic density of states and strong enhancement of quantum dot luminescence. This explains the results of recent experiments [T. Ozel et al., ACS Nano 5, 1328 (2011)] and confirms that hyperbolic metamaterials are capable of increasing the radiative decay rate of emission centers inside them. The proposed theoretical framework can also be used to design quantum-dot/nanoplasmonic composites with optimized luminescence enhancement. (C) 2014 Optical Society of America
Open Access
Optical properties of metamaterial-based devices modulated by a liquid crystal
(Springer Berlin Heidelberg, 2014) Karaomerlioglu, F.; Mamedov, A. M.; Özbay, Ekmel
Due to the fact that it is possible to manipulate light with photonic crystals (PCs), PCs hold a great potential for designing new optical devices. There has been an increase in research on tuning the optical properties of PCs to design devices. We presented a numerical study of optical properties of metamaterial-based devices by liquid crystal infiltration. The plane wave expansion method and finite-difference time-domain method for both TE and TM modes revealed optical properties in photonic crystal structures in an air background for a square lattice. E7 type has been used as a nematic liquid crystal and SrTiO3 as a ferroelectric material. We showed the possibility of the metamaterials for a two-dimensional photonic crystal cavity on a ferroelectric base infiltrated with a nematic liquid crystal.
Open Access
Sub-wavelength resolution in a photonic crystal superlens
(2003) Çubukçu, Ertuğrul
Materials that can bend light in the opposite direction to normal (’left-handed’ materials) reverse the way in which refraction usually works-this negative refractive index is due to simultaneously negative permeability and permittivity. Here we demonstrate negative refraction of electromagnetic waves in a two-dimensional dielectric photonic crystal that has a periodically modulated positive permeability and a permeability of unity. This experimental verification of negative refraction is a step towards the realization of a ’superlens’ that will be able to focus features smaller than the wavelength of light. Our structure consists of a square array of alumina rods in air. To obtain the frequency range within which the negative refraction and the other peculiar properties incorporated with it, we have calculated the the equal frequency contours of our photonic crystal with the photonic plane wave expansion method. We found out that 13.7 GHz is the optimum frequency for negative refraction. We took transmission measurements to confirm our structure’s predicted negative refraction: we used the the interfaces of the photonic crystal in the Γ − M direction. Our experiments were simulated with the finite-difference time-domain method (FDTD). The negative index of refraction was determined to be −1.94, which is close to the theoretical value of −2.06 calculated by the FDTD method. Since we know that we have a negative refractive material , we used our crystal to test the superlensing effect that was predicted for negative refractive materials. We have demonstrated that the image of two coherent point sources separated by a distance of λ/3 can be resolved. We have extended our approach to the case with two incoherent point sources, and we have achieved subwavelength resolution for this configuration as well. To our knowledge, this is the first demonstration of subwavelength resolution of electromagnetic waves in a negative index material.
Open Access
Tight-binding mechanism in slow light regime
(IEEE, 2011) Akosman, Ahmet Emin; Mutlu, Mehmet; Kurt, Hamza; Özbay, Ekmel
In this study, tight-binding formalism is applied to a photonic crystal coupled cavity structure in order to investigate the characteristics of ultra slow light modes. Eigen-mode splitting is observed and resulting group indices obtained from the tight-binding formalism and numerical results are compared. © 2011 IEEE.