Focusing surface plasmons via changing the incident angle

Cataloged from PDF version of article.We report a circular metallic aperture with a subwavelength circular slit in the microwave regime, in which we experimentally demonstrate that this aperture can excite and focus surface plasmons. Under normal illumination, there is no focusing of the surface plasmons. However, by changing the incident angle, it is possible to focus surface plasmons. We showed that under a 20 degrees illumination angle surface plasmons focus at 4 cm away from the center on the surface of the aperture. (C) 2008 American Institute of Physics

Highly directive radiation from sources embedded inside photonic crystals

Cataloged from PDF version of article.In this work, we have experimentally and theoretically studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal. Half power beam widths as small as 6degrees have been obtained. Our results also show that the angular distribution of power strongly depends on the frequency and on the size of the photonic crystal. (C) 2003 American Institute of Physics

Subwavelength resolution with a negative-index metamaterial superlens

Cataloged from PDF version of article.Negative-index metamaterials are candidates for imaging objects with sizes smaller than a half-wavelength. The authors report an impedance-matched, low loss negative-index metamaterial superlens that is capable of resolving subwavelength features of a point source with a 0.13 lambda resolution, which is the highest resolution achieved by a negative-index metamaterial. By separating two point sources with a distance of lambda/8, they were able to detect two distinct peaks on the image plane. They also showed that the metamaterial based structure has a flat lens behavior. (c) 2007 American Institute of Physics

Experimental demonstration of subwavelength focusing of electromagnetic waves by labyrinth-based two-dimensional metamaterials

Cataloged from PDF version of article.We studied focusing in a two-dimensional metamaterial that was based on a labyrinth structure. We theoretically showed that the labyrinth-based metamaterial exhibits negative indices of refraction between 6 and 6.4 GlIz. We experimentally studied the focusing effect by measuring electric field intensities on the output side of the metamaterial when the source was placed in front of the input side of the metamaterial. Our experimental results showed that it is in fact possible to focus the source field with half-widths as small as lambda/4 by using the labyrinth-based metamaterial. (c) 2006 Optical Society of America

Beaming of light and enhanced transmission via surface modes of photonic crystals

Cataloged from PDF version of article.We report beaming and enhanced transmission of electromagnetic waves by use of surface corrugated photonic crystals. The modes of a finite-size photonic crystal composed of dielectric rods in free space have been analyzed by the plane-wave expansion method. We show the existence of surface propagating modes when the surface of the finite-size photonic crystal is corrugated. We theoretically and experimentally demonstrate that the transmission through photonic crystal waveguides can be substantially increased by the existence of surface propagating modes at the input surface. In addition, the power emitted from the photonic crystal waveguide is confined to a narrow angular region when an appropriate surface corrugation is added to the output surface of the photonic crystal. © 2005 Optical Society of Americ

Off-axis beaming from subwavelength apertures

Cataloged from PDF version of article.Photonic crystal waveguides and metallic subwavelength apertures are promising tools for light manipulation. It is possible to obtain enhanced directional beams by using these structures via coupling to surface waves. In addition, these apertures can be designed to steer such directional beams by introducing asymmetrical gratings on the output surface. In the present paper, we report directional yet off-axis beaming from subwavelength apertures at microwave frequencies. The full width at half maximum of the beam is 10 degrees while the beaming angle is 15 degrees. Our results show that it is possible to steer the beam by the appropriate modification of the output surface. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2990063

Field-effect-assisted photoconductivity in PbS films deposited on silicon dioxide

Cataloged from PDF version of article.Lead sulfide (PbS) thin films were deposited from a chemical bath onto SiO2/Si (n-type) substrates. Pseudo-metal-oxide-semiconductor devices were obtained by evaporating source and drain gold electrodes on a PbS surface and aluminum gate electrode on a Si substrate. Field-effect-assisted photoconductivity in the PbS layer was investigated at room temperature, in the 800-2700-nm-wavelength domain for different values and polarities of the drain and gate voltages. The best results were obtained for a positive gate, when both semiconductors are in depletion. An enhancement of about 25% of the photoconductive signal is obtained compared with the case when the gate electrode is absent or is not used. A simple model is proposed that explains the behavior of the dark current and photoconductive signal in PbS film with changing the gate voltage. (C) 2002 American Institute of Physics

Experimental observation of subwavelength localization using metamaterial-based cavities

Cataloged from PDF version of article.We report subwavelength localization of electromagnetic fields within cavities based on metamaterials. Cavity resonances are observed in the transmission spectrum of a split-ring resonator and composite metamaterials cavity structures. These cavity resonances are shown to exhibit high-quality factors. Since the unit cells of metamaterials are much smaller than the operation wavelength, subwavelength localization is possible within these metamaterial cavity structures. In the present Letter, we show that the electromagnetic field is localized into a region of λ/8, where λ is the cavity resonance wavelength. © 2008 Optical Society of America

Experimental observation of cavity formation in composite metamaterials

Cataloged from PDF version of article.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

Dwell-time computation for stability of switched systems with time delays

Cataloged from PDF version of article.The aim of this study is to find an improved dwell time that guarantees the stability of switched systems with heterogeneous constant time-delays. Piecewise Lyapunov-Krasovkii functionals are used for each candidate system to investigate the stability of the switched time-delayed system. Under the assumption that each candidate system is stable for small delay values, a sufficient condition for dwell-time that guarantees the asymptotic stability is derived. Numerical examples are given to compare the results with the previously obtained dwell-time bounds. © The Institution of Engineering and Technology 2013