Unidirectional transmission in non-symmetric gratings containing metallic layers

Cataloged from PDF version of article.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. (C) 2009 Optical Society of Americ

Isolation and one-way effects in diffraction on dielectric gratings with plasmonic inserts

Cataloged from PDF version of article.Diffraction of plane waves on dielectric gratings with planar plasmonic inserts is studied with the emphasis put on the anomalous selectivity of diffraction orders. It is shown that some formally propagating orders can be suppressed within a wide frequency range. The effect of suppression is more general than the isolation effect observed earlier in zero-permittivity and (near-)zero-index slabs and sensitive to the frequency dependent peculiarities of the field distribution within the plasmonic layer. It is required that the real part of the permittivity of this layer is positive less than unity. The wideband features of the suppression effect, i.e., one-way transmission and diffraction-free reflection are demonstrated. Narrowband selectivity effects are also studied. The structures suggested can be used for extending the potential of technologies that are based on multibeam operation and field transformation. (C) 2008 Optical Society of Americ

One-way Rayleigh-Wood anomalies and tunable narrowband transmission in photonic crystal gratings with broken structural symmetry

Cataloged from PDF version of article.In photonic crystal (PC) gratings whose structural symmetry is broken owing to one-side corrugations, the Rayleigh-Wood anomalies can appear in a one-way manner. In the combination with the vanishing coupling to the lowest Floquet-Bloch mode at the upper band edge, these anomalies lead to the appearance of the defect-mode-like, i.e., very narrow one-way transmission, peak, which cannot appear in the corresponding slab of PC without corrugations. Such a sole peak can be transformed into a one-way transmission band with a desired width by varying angle of incidence. The nonoverlapping and thus switchable one-way (higher-order) and two-way (zero-order) transmission bands can be obtained in both the frequency and incidence-angle domains. Adjustment of PC lattice and corrugation parameters allows one to obtain two subsequent one-way bands, every being connected with a certain higher diffraction order. Conditions required for the appearance of a narrow one-way transmission band in the vicinity of a Rayleigh-Wood anomaly are well consistent with typical dispersion features of a very large class of PCs and do not need unusual performances

Toward photonic crystal based spatial filters with wide angle ranges of total transmission

Cataloged from PDF version of article.Spatial filters with steep switching between wide ranges of total transmission and total reflection can be obtained by using two-dimensional dielectric photonic crystals, which are a few wavelengths thick. The guidelines for engineering bandpass and bandstop filters are given. The flatness of isofrequency contours that are localized around a periphery point of the first Brillouin zone is a necessary but insufficient condition for the existence of wide angle ranges of total transmission at intermediate and large angles of incidence. Such ranges that are wider than 20 degrees are demonstrated

Multichannel optical diode with unidirectional diffraction relevant total transmission

Cataloged from PDF version of article.We will show that broadband unidirectional optical transmission with a total transmission maximum inside the band can be obtained for linearly polarized incident waves in the nonsymmetric photonic crystal gratings made of isotropic linear materials at a fixed nonzero or zero angle of incidence. Being based on the merging of diffraction and dispersion effects, the basic physical mechanism studied exploits the transmission channels associated with higher orders, for which asymmetry in the coupling conditions at the two grating interfaces appears when spatial inversion symmetry is broken. Total transmission in one direction and zero transmission in the opposite direction can be obtained due to hybridization of Fabry-Perot type resonances with a diffraction anomaly that yields a diode-like operation regime. Single-beam deflection and two-beam splitting can be obtained, for which transmission can be (nearly) total, if the corrugated side is illuminated. In contrast to the previous studies, it is also shown that unidirectional transmission can appear only at a fixed frequency and only due to diffractions, when total transmission occurs at the noncorrugated-side illumination, being in agreement with the Lorentz Lemma. (c) 2012 Optical Society of America

Near-field light localization using subwavelength apertures incorporated with metamaterials

Cataloged from PDF version of article.We report strong near-field electromagnetic localization by using subwavelength apertures and metamaterials that operate at microwave frequencies. We designed split ring resonators with distinct configurations in order to obtain extraordinary transmission results. Furthermore, we analyzed the field localization and focusing characteristics of the transmitted evanescent waves. The employed metamaterial configurations yielded an improvement on the transmission efficiency on the order of 27 dB and 50 dB for the deep subwavelength apertures. The metamaterial loaded apertures are considered as a total system that offered spot size conversion ratios as high as 7.12 and 9.11 for the corresponding metamaterial configurations. The proposed system is shown to intensify the electric fields of the source located in the near-field. It also narrows down the electromagnetic waves such that a full width at half maximum value of λ/29 is obtained. © 2012 Elsevier B.V. All rights reserved

PID controller design for fractional-order systems with time delays

Cataloged from PDF version of article.Classical proper PID controllers are designed for linear time invariant plants whose transfer functions are rational functions of s(alpha), where 0 < alpha < 1, and s is the Laplace transform variable. Effect of input-output time delay on the range of allowable controller parameters is investigated. The allowable PID controller parameters are determined from a small gain type of argument used earlier for finite dimensional plants. (C) 2011 Elsevier B.V. All rights reserved

LSPR enhanced MSM UV photodetectors

Cataloged from PDF version of article.We fabricated localized surface plasmon resonance enhanced UV photodetectors on MOCVD grown semi-insulating GaN. Plasmonic resonance in the UV region was attained using 36nm diameter Al nanoparticles. Extinction spectra of the nanoparticles were measured through spectral transmission measurements. A resonant extinction peak around 300nm was obtained with Al nanoparticles. These particles gave rise to enhanced absorption in GaN at 340nm. Spectral responsivity measurements revealed an enhancement factor of 1.5. These results provided experimental verification for obtaining field enhancement by using Al nanoparticles on GaN. © 2012 IOP Publishing Ltd

Organic semiconductor-based photonic crystals for solar cell arrays: band gap and optical properties

Cataloged from PDF version of article.Photonic crystals (PCs) hold great potential for designing new optical devices because of the possibility of the manipulation of light with PCs. There has been an increase in research on tuning the optical properties of PCs to design devices. We design organic semiconductor-based PC structures and calculate optical properties using the plane wave expansion method and finite-difference time-domain method in an air background for a hexagonal lattice. We showed the possibility of the solar cell arrays for a 2D PC cavity on an organic semiconductor base infiltrated with a nematic liquid crystal. E7 type has been used as a nematic liquid crystal and 4,4-Bis[4-(diphenylamino) styryl]biphenyl as an organic semiconductor material