Results 1 - 10 of 12092
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[en] In this paper, a miniaturized patch antenna (MPA) with Zero Index Metamaterial (ZIM) as Superstrate at 518 MHz is designed and fabricated. The proposed method is utilized for retrieving the effective properties, i.e., impedance, refractive index, as well as the permittivity, and permeability of the unit cell. We have investigated the effect of distance between the antenna and the Superstrate on performance of the antenna. Moreover, the performance of the antenna is evaluated by both simulations and measurements. The results of our study have shown more directional and higher gain patch antennas. Also, a good agreement between the measured and the simulation values is found. It is demonstrated that the gain of antenna, having the ZIM Superstrate, is much higher compared to the one without the ZIM superstrate. Furthermore, the mean value of the gain for the proposed Metamaterial antenna (which is Superstrate-based) is considerably improved from −1.9 to 3.97 dBi comparing to the patch antenna alone. In fact, the directivity of the antenna is dramatically improved based on the zero refraction properties of the Metamaterial. (paper)
[en] Topological insulators are materials that conduct on the surface and insulate in their interior due to non-trivial topology of the band structure. The edge states on the interface between topological (non-trivial) and conventional (trivial) insulators are topologically protected from scattering due to structural defects and disorders. Recently, it was shown that photonic crystals (PCs) can serve as a platform for realizing a scatter-free propagation of light waves. In conventional PCs, imperfections, structural disorders, and surface roughness lead to significant losses. The breakthrough in overcoming these problems is likely to come from the synergy of the topological PCs and silicon-based photonics technology that enables high integration density, lossless propagation, and immunity to fabrication imperfections. For many applications, reconfigurability and capability to control the propagation of these non-trivial photonic edge states is essential. One way to facilitate such dynamic control is to use liquid crystals (LCs), which allow to modify the refractive index with external electric field. Here, we demonstrate dynamic control of topological edge states by modifying the refractive index of a LC background medium. Background index is changed depending on the orientation of a LC, while preserving the topology of the system. This results in a change of the spectral position of the photonic bandgap and the topological edge states. The proposed concept might be implemented using conventional semiconductor technology, and can be used for robust energy transport in integrated photonic devices, all-optical circuity, and optical communication systems. (paper)
[en] This study presents active beam steering and afocal zooming of light by incorporating liquid crystals (LCs) with graded index photonic crystals (GRIN PCs). The GRIN PC structures are composed of low refractive index polymer annular rods with holes of gradually varying radii. To actively manipulate incident light, the annular rods are infiltrated with nematic LCs. By applying an external voltage to the infiltrated LCs, the effective index profile of the low-index GRIN PC structure is modulated without introducing any mechanical movement. The incident beam deflection and corresponding focal distance modulation are tuned only by controlling the applied bias voltage. In the present work, the hyperbolic secant refractive index profile is chosen to design GRIN PC structures. To design a GRIN PC structure with annular PCs, the Maxwell–Garnett effective medium approximation is employed. We analytically express the relation between infiltrated LCs and the gradient parameter to show the physical background of the tuning ability of the proposed devices. Beam steering and afocal zooming devices are analytically investigated via geometrical optics, and numerically realized with the help of a finite-difference time-domain method. A beam deflection with an angle change of Δθ out = 44° and a light magnification with maximum ×2.15 are obtained within operating frequencies of a/λ = [0.10–0.15] and a/λ = [0.15–0.25], respectively, where ‘a’ is the lattice constant and λ is the incident wavelength. The corresponding operating frequency bandwidths are calculated as 40% and 50% for the beam steering and afocal zooming applications, respectively. LCs are inexpensive materials and work under low voltage/power conditions. This feature can be used for designing an electro–optic GRIN PC device that has the potential for use in a wide variety of optical applications. (paper)
[en] We propose a variable-path interferometric technique for the measurement of the absolute refractive index of optical glasses. We use two interferometers to decide the ratio between changes in the optical path in a prism-shaped sample glass and in air resulting from displacement of the sample. The method allows precise measurements to be made without prior knowledge of the properties of the sample. The combined standard uncertainty of the proposed method is 1.6x10-6
[en] Highlights: • SPR discriminates and monitors two molecules simultaneously binding to a surface. • Accurate concentration determination of two different molecules simultaneously. • Deconstruction of a sum sensorgram into two molecular component sensorgrams. • Simultaneous measurement of binding constants of two binding molecules in a mixture. • Applicability to allosteric effects, bi-specific binders, and conformation changes. Surface plasmon resonance (SPR) is a well-established method for biomolecular interaction studies. SPR monitors the binding of molecules to a solid surface, embodied as refractive index changes close to the surface. One limitation of conventional SPR is the universal nature of the detection that results in an inability to qualitatively discriminate between different binding species. Furthermore, it is impossible to directly discriminate two species simultaneously binding to different sites on a protein, which limits the utility of SPR, for example, in the study of allosteric binders or bi-specific molecules. It is also impossible in principle to discriminate protein conformation changes from actual binding events. Here we demonstrate how Label-Enhanced SPR can be utilized to discriminate and quantitatively monitor the simultaneous binding of two different species – one dye-labeled and one unlabeled - on a standard, single-wavelength SPR instrument. This new technique increases the versatility of SPR technology by opening up application areas where the usefulness of the approach has previously been limited.
[en] An optical differentiator based on a three-layer resonant structure with a W-shaped refractive index profile is proposed. The differentiation operation is performed in reflection and is associated with the resonant excitation of an eigenmode of the structure localized in the central layer. The presented results of numerical simulations demonstrate the possibility of spatial differentiation of the transverse profile of an incident optical beam, temporal differentiation of the envelope of an incident optical beam, and simultaneous spatial and temporal differentiation with a high quality. The proposed structure can find applications in designing analog optical computing and optical information processing systems.
[en] In this work we investigate the ballistic transport of electrons through three-terminal graphene-based devices. The system consists of a Y-shaped junction formed by three armchair-edged graphene nanoribbons with a rectangular gate potential applied to one of the output branches, whereby current control can be established by the controlling of the refractive index in graphene p–n junctions. Transport properties are obtained by using the Landauer–Büttiker formalism and the tight-binding model within the nearest-neighbor approximation, which allows the calculation of the conductance as function of the Fermi energy, the applied potential, and the system size, as well as the current density. The results demonstrate that the applied electric field can tune the current transmission between the input and two output leads and, consequently, the proposed system acts as a current switch. (paper)