Sharif Digital Repository

In this paper we introduce a coupled system of two quantum bits residing at the interface of a heterostructure device. The structure encompasses a reference quantum bit, a photonic/plasmonic crystal waveguide and an obedient quantum bit. Each quantum bit is an electronic device which is designed based on an anti-dot lattice of two-dimensional electron gas in heterostructures. By applying a potential gate in the aforementioned structure it is possible to control electronic tunneling rate and hence quantum bits' swapping frequency. Coupling through the plasmonic waveguide may be employed to entangle quantum bits. The waveguide has been designed by exploiting conducting islands of... 

A theory is presented for the quantum radiation emitted from a single exciton in a quantum dot. We assume that the quantum dot is in strong coupling to a slab photonic crystal cavity. A dielectric function of spatial coordinates is used to explain the effects of the macroscopic medium. It has been proved that the electric field in such a medium can be described using the so-called K-function. We derive a formula for obtaining the frequency spectrum, and present an analytical result for the optical spectrum, which is dependent on the K-function. We also have considered a slab photonic crystal configuration with hexagonal structure containing a cavity to evaluate the frequency spectrum in such... 

A method to simulate an open boundary problem within the finite difference time domain approach for the emission of photo-conductive antennas is presented here. For this purpose, we use convolutional perfectly matched layers (CPMLs). In these devices, the semiconductor region, where transient currents are present in simulation time, is considered to be an 'active' medium. This medium is extended virtually beyond its boundaries or the computational domain limits. We explain in this communication how to simulate the transient state of a semiconductor in a CPML region as well as the potential of the method developed to solve conventional practical applications  

Subradiant modes can exhibit sharper spectral response, and lower radiative loss compared to the super-radiant modes of plasmonic nanostructures. Selective excitation of these modes is challenging, and has practical importance. In this paper, a systematic procedure for determining, and individually exciting the subradiant modes of a plasmonic nanostructure is presented by utilizing our previously reported T-matrix formulation. As an example, we calculate various modes of a gold nanodimer, and determine the incident field required for exciting a subradiant mode of this nanostructure. This field is then generated by a modified zone plate lens. The expansion of scattered field, as well as the... 

Passive localisation of non-cooperative targets through their electromagnetic emissions is an attractive issue. This localisation task can be carried out using multitude of receiver sites being linked together. This multiplicity, however, brings about difficulties in organising and coordinating the sites. One can even claim that the method is no longer passive considering the necessary communication links between the sites. On the other hand, single-site localisation methods basically overcome these difficulties eliminating the need for inter-site communications. In this study, a single-site localisation method is presented and analysed. This method is applicable to scenarios with a large... 

An inverted organic solar cell (IOSC) with nanograting array as anode of the cell has been simulated and analyzed using a combined electrical and optical approach. We have used finite difference time domain (FDTD) method for optimizing device structure. We have compared the characteristics of the IOSC with grating structure with a reference IOSC without grating structure. As a result, an improvement of 11% and 26% in power conversion efficiency (PCE) and short circuit current (JSC) compared to the reference structure was achieved. An analysis is provided on the origin of reduced fill factor (FF) in the IOSC with grating structure. We also have discussed about disadvantage of using optical... 

A novel plane-wave-based approach for analytical treatment of dispersive relation is developed and applied to analyze the behavior of electromagnetic waves in plasmonic-photonic-crystal slabs. Here Drude model is used for describing frequency dependent permittivity of plasma rods in host dielectric medium. In the present work, dispersion relation below and above the light line is calculated approximately by means of Maxwell-Garnett effective medium and Revised Plane Wave Method (RPWM). The eigen-functions are then used in Revised Guided Mode Expansion (RGME) as the set of orthonormal bases. Following this procedure, the accurate band structure is obtained. In these kind of methods there are... 

Low power operation and high speed have always been desirable in applications such as data processing and telecommunications. While achieving these two goals simultaneously, however, one encounters the well-known powerbandwidth trade-off. This is here discussed in a typical bistable switch based on a two-dimensional photonic crystal with Kerr type nonlinearity. The discussion is supported by the nonlinear finite difference time domain (FDTD) simulation of a direct coupled structure with a home-developed code. Two cases of working near resonant and off- resonant are simulated to compare the power and the speed of the device in the two cases. It is shown that working nearresonance reduces the... 

In this paper, it is shown that non-reciprocity can be observed in time-varying media without employing spatiotemporal modulated permittivities. We show that by using only two one-dimensional Fabry–Perot slabs with time-periodic permittivities having quadrature-phase difference, it is possible to achieve considerable non-reciprocity in transmission at the incidence frequency. To analyze such a scenario, generalized transfer matrices are introduced to find the wave amplitudes of all harmonics in all space. The results are verified by in-house finite-difference time-domain simulations. Moreover, in order to have a simple model of such time-varying slab resonators, a time-perturbed coupled-mode... 

This paper is concerned with the investigation of an optical band-pass filter based on subwavelength surface plasmon polaritons. The transmission characteristics are numerically analyzed by the finite-difference time-domain method, and simulation results reveal that the structure has a band-pass filtering characteristic. The metal–insulator–metal plasmonic nanostructure is implemented by several vertical rectangular cavities across an optical waveguide. The metal and dielectric materials utilized for the realization of the filter are silver and air, respectively. Furthermore, the performance can be efficiently modified by tuning the geometric parameters such as the cavities’ length and width... 

We report the effect of the geometric parameters on transparency and conductivity in a metallic nanowire mesh as a transparent electrode. Today, indium tin oxide and fluorine-doped tin oxide are used as the transparent electrode for displays and solar cells. Still, there is a definite need for their replacement due to drawbacks such as brittleness, scarcity, and adverse environmental effects. Metallic nanowire mesh is likely the best replacement option, but the main issue is how to find the optimal structure and how to get the best performance. Since the interaction of light with nanowire mesh is complicated, there is no straightforward rule with a simple analytical solution. We developed a... 

The propagation of intense optical beams in a gas undergoing ionization is analyzed through a threedimensional finite-difference time-domain (3D-FDTD) scheme. The propagation dynamics include the effects of diffraction, nonlinear self-focusing, and ionization. For sufficiently intense optical beams the neutral gas undergoes ionization, generating a plasma which tends to defocus the beam. Balancing of diffraction, plasma defocusing, and nonlinear self-focusing may lead to self-guided results. In this paper, necessary relations have been introduced into the conventional FDTD formulation to account for the nonlinear behaviors. Furthermore, a concurrent utilization of computer memory and disk... 

Through using a three-dimensional finitedifference time-domain (3D-FDTD) scheme, we analyze nonlinear self-focusing in air as a Kerr medium. For sufficiently intense laser beams, the gaseous medium can behave as a strong positive lens which tends to focus the beam. Our simulations' major focus is on the propagation characteristics of an intense continuous-wave laser beam. Necessary relations have been introduced into the conventional FDTD formulation to account for the nonlinear behavior of air. The results clearly indicate that sufficient amounts of optical intensity may lead to self-focusing immediately in front of the laser aperture. ©2008 IEEE  

A rigorous, fast and efficient method is proposed for analytical extraction of guided defect modes in two-dimensional photonic crystals, where each Bloch spatial harmonic is expanded in terms of Hermite-Gauss functions. This expansion, after being substituted in Maxwell's equations, is analytically projected in the Hilbert space spanned by the Hermite-Gauss basis functions, and then a new set of first order coupled linear ordinary differential equations with non-constant coefficients is obtained. This set of equations is solved by employing successive differential transfer matrices, whereupon defect modes, i.e. the guided modes propagating in the straight line-defect photonic crystal... 

NMZ ferrites doped with rare earth having spinel composition Ni0.5Mn0.3Zn0.2X0.02Fe1.98O4, whereas X = Y, Pr and Gd were synthesized by sol gel auto-ignition method. XRD, FESEM, VSM and VNA were used to determine the phase, microstructural, magnetic and electromagnetic properties of rare earths doped NMZ ferrite. XRD analysis confirms the single phase of the rare earths doped NMZ ferrite. FESEM images shows Pr doped NMZ ferrite has less agglomerations and more porous structure as compared to NMZ and other rare earths doped NMZ ferrites. Magnetic analysis shows the enhancement in saturation magnetization and remanence with the doping of Y, Pr and Gd in NMZ ferrite. Dielectric properties were... 

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were... 

NMZ ferrites doped with rare earth having spinel composition Ni0.5Mn0.3Zn0.2X0.02Fe1.98O4, whereas X = Y, Pr and Gd were synthesized by sol gel auto-ignition method. XRD, FESEM, VSM and VNA were used to determine the phase, microstructural, magnetic and electromagnetic properties of rare earths doped NMZ ferrite. XRD analysis confirms the single phase of the rare earths doped NMZ ferrite. FESEM images shows Pr doped NMZ ferrite has less agglomerations and more porous structure as compared to NMZ and other rare earths doped NMZ ferrites. Magnetic analysis shows the enhancement in saturation magnetization and remanence with the doping of Y, Pr and Gd in NMZ ferrite. Dielectric properties were... 

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were... 

Plasmonic nanostructures have emerging applications in solar cells, photodynamic therapies, surface-enhanced Raman scattering detection, and photocatalysis due to the excitation of localized surface plasmons. The exciting electric field resulting from the collective oscillation of free electrons is highly dependent on the dielectric medium, shape, size, composition, and configuration of plasmonic nanostructures. From an engineering perspective, one can tune the optimal properties in the desired applications of geometrical parameters such as the shape, size, and nanoparticles' configuration. Such optimization should be performed analytically (with exact solutions) or numerically (with... 

In this paper a wave approach has been introduced to study the performance of a distributed amplifier. The time domain response of a FET is obtained by means of the fully distributed model. By applying the procedure to a pi-gate GaAs MESFET, the S matrix is computed from time domain results over a frequency range of 2-20 GHz. Scattering parameters of gate and drain lines are extracted from three-dimensional FDTD simulation. The result obtained by this wave approach is compared with device lumped model and Quasi static approach of transmission line. © 2007 IEEE