Browsing by Subject "computer simulation"

Now showing 1 - 8 of 8

Open Access
Asymmetric light propagation in chirped photonic crystal waveguides
(Optical Society of American (OSA), 2012) Kurt H.; Yilmaz, D.; Akosman, A.E.; Özbay, Ekmel
We 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.
Open Access
Compact wavelength de-multiplexer design using slow light regime of photonic crystal waveguides
(Optical Society of American (OSA), 2011) Akosman, A.E.; Mutlu, M.; Kurt H.; Özbay, Ekmel
We demonstrate the operation of a compact wavelength demultiplexer using cascaded single-mode photonic crystal waveguides utilizing the slow light regime. By altering the dielectric filling factors of each waveguide segment, we numerically and experimentally show that different frequencies are separated at different locations along the waveguide. In other words, the beams of different wavelengths are spatially dropped along the transverse to the propagation direction. We numerically verified the spatial shifts of certain wavelengths by using the two-dimensional finite-difference time-domain method. The presented design can be extended to de-multiplex more wavelengths by concatenating additional photonic crystal waveguides with different filling factors. © 2011 Optical Society of America.
Open Access
Experimental observation of cavity formation in composite metamaterials
(Optical Society of American (OSA), 2008) Caglayan H.; Bulu I.; Loncar, M.; Özbay, Ekmel
In this paper, we investigated one of the promising applications of left-handed metamaterials: composite metamaterial based cavities. Four different cavity structures operating in the microwave regime were constructed, and we observed cavity modes on the transmission spectrum with different quality factors. The effective permittivity and permeability of the CMM structure and cavity structure were calculated by use of a retrieval procedure. Subsequently, in taking full advantage of the effective medium theory, we modeled CMM based cavities as one dimensional Fabry-Perot resonators with a subwavelength cavity at the center. We calculated the transmission from the Fabry-Perot resonator model using the one-dimensional transfer matrix method, which is in good agreement with the measured result. Finally, we investigated the Fabry-Perot resonance phase condition for a CMM based cavity, in which the condition was satisfied at the cavity frequency. Therefore, our results show that it is possible to treat metamaterial based cavities as one-dimensional Fabry-Perot resonators with a subwavelength cavity. © 2008 Optical Society of America.
Open Access
Influence of phase function on modeled optical response of nanoparticle-labeled epithelial tissues
(2011) Cihan, C.; Arifler, D.
Metal nanoparticles can be functionalized with biomolecules to selectively localize in precancerous tissues and can act as optical contrast enhancers for reflectance-based diagnosis of epithelial precancer. We carry out Monte Carlo (MC) simulations to analyze photon propagation through nanoparticle-labeled tissues and to reveal the importance of using a proper form of phase function for modeling purposes. We first employ modified phase functions generated with a weighting scheme that accounts for the relative scattering strengths of unlabeled tissue and nanoparticles. To present a comparative analysis, we repeat ourMCsimulations with simplified functions that only approximate the angular scattering properties of labeled tissues. The results obtained for common optical sensor geometries and biologically relevant labeling schemes indicate that the exact form of the phase function used as model input plays an important role in determining the reflectance response and approximating functions often prove inadequate in predicting the extent of contrast enhancement due to labeling. Detected reflectance intensities computed with different phase functions can differ up to ̃60% and such a significant deviation may even alter the perceived contrast profile. These results need to be taken into account when developing photon propagation models to assess the diagnostic potential of nanoparticle-enhanced optical measurements. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).
Open Access
Surface wave splitter based on metallic gratings with sub-wavelength aperture
(Optical Society of American (OSA), 2008) Caglayan H.; Özbay, Ekmel
We investigated the splitting of surface electromagnetic waves trapped at the output surface of a one-dimensional metallic grating structure. The output gratings of the structure asymmetrically such that the output surfaces at the different sides of the subwavelength aperture can support surface waves at different frequencies. The transmission amplitude as measured at the left side is 1,000 times of that at the right side at 16 GHz. At 24 GHz, the transmission measured at the right side is 20 times that of the left side of the structure. Therefore, surface waves are guided into the different sides of the aperture at different frequencies via metallic gratings. The experimental results are in agreement with the theoretical results. © 2008 Optical Society of America.
Open Access
Understanding the plasmonic properties of dewetting formed Ag nanoparticles for large area solar cell applications
(Optical Society of American (OSA), 2013) Günendi, M.C.; Tanyeli I.; Akgüç G.B.; Bek, A.; Turan, R.; Gülseren O.
The effects of substrates with technological interest for solar cell industry are examined on the plasmonic properties of Ag nanoparticles fabricated by dewetting technique. Both surface matching (boundary element) and propagator (finite difference time domain) methods are used in numerical simulations to describe plasmonic properties and to interpret experimental data. The uncertainty on the locations of nanoparticles by the substrate in experiment is explained by the simulations of various Ag nanoparticle configurations. The change in plasmon resonance due to the location of nanoparticles with respect to the substrate, interactions among them, their shapes, and sizes as well as dielectric properties of substrate are discussed theoretically and implications of these for the experiment are deliberated. ©2013 Optical Society of America.
Open Access
Unidirectional transmission in non-symmetric gratings containing metallic layers
(Optical Society of American (OSA), 2009) Serebryannikov, A.E.; Özbay, Ekmel
The 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.
Open Access
Unidirectional transmission in photonic-crystal gratings at beam-type illumination
(Optical Society of American (OSA), 2010) Cakmak, A.O.; Colak, E.; Serebryannikov, A.E.; Özbay, Ekmel
Unidirectional transmission is studied theoretically and experimentally for the gratings with one-side corrugations (non-symmetric gratings), which are based on two-dimensional photonic crystals composed of alumina rods. The unidirectional transmission appears at a fixed angle of incidence as a combined effect of the peculiar dispersion features of the photonic crystal and the properly designed corrugations. It is shown that the basic unidirectional transmission characteristics, which are observed at a plane-wave illumination, are preserved at Gaussian-beam and horn antenna illuminations. The main attention is paid to the single-beam unidirectional regime, which is associated with the strong directional selectivity arising due to the first negative diffraction order. An additional degree of freedom for controlling the transmission of the electromagnetic waves is obtained by making use of the asymmetric corrugations at the photonic crystal interface. © 2010 Optical Society of America.