M. A. Alsunaidi

Electromagnetic wave effects on microwave transistors using a full-wave time-domain model

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FETs) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwells equations to the active device model. The active device model is based on the moments of the Boltzmanns transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwells equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FETs. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies.

A General ADE-FDTD Algorithm for the Simulation of Dispersive Structures

A finite-difference time-domain general algorithm, based on the auxiliary differential equation (ADE) technique, for the analysis of dispersive structures is presented. The algorithm is suited for cases where materials having different types of dispersion are modeled together. While having the same level of accuracy, the proposed algorithm finds its strength in unifying the formulation of different dispersion models into one form. Consequently, savings in both memory and computational requirements, compared to other ADE-based methods that model each dispersion type separately, are possible. The algorithm is applied in the simulation of surface plasmon polaritons using the multipole Lorentz-Drude dispersion model of silver.

A time-domain algorithm for the analysis of second-harmonic generation in nonlinear optical structures

A time-domain simulator of integrated optical structures containing second-order nonlinearities is presented. The simulation algorithm is based on nonlinear wave equations representing the propagating fields and is solved using the finite-difference time-domain method. The simulation results for a continuous-wave operation are compared with beam propagation method simulations showing excellent agreement for the particular examples considered. Because the proposed algorithm does not suffer from the inaccuracies associated with the paraxial approximation, it should find application in a wide range of device structures and in the analysis of short-pulse propagation in second-order nonlinear devices.

A Simple FDTD Algorithm for Simulating EM-Wave Propagation in General Dispersive Anisotropic Material

In this paper, an finite-difference time-domain (FDTD) algorithm for simulating propagation of EM waves in anisotropic material is presented. The algorithm is based on the auxiliary differential equation and the general polarization formulation. In anisotropic materials, electric fields are coupled and elements in the permittivity tensor are, in general, multiterm dispersive. The presented algorithm resolves the field coupling using a formulation based on electric polarizations. It also offers a simple procedure for the treatment of multiterm dispersion in the FDTD scheme. The algorithm is tested by simulating wave propagation in 1-D magnetized plasma showing excellent agreement with analytical solutions. Extension of the algorithm to multidimensional structures is straightforward. The presented algorithm is efficient and simple compared to other algorithms found in the literature.

Electron irradiation induced reduction of the permittivity in chalcogenide glass (As2S3) thin film

In this paper, we investigate the effect of electron beam irradiation on the dielectric properties of As2S3 chalcogenide glass. By means of low-loss electron energy loss spectroscopy, we derive the permittivity function, its dispersive relation, and calculate the refractive index and absorption coefficients under the constant permeability approximation. The measured and calculated results show a heretofore unseen phenomenon: a reduction in the permittivity of ≥40%. Consequently a reduction of the refractive index of 20%, hence, suggests a conspicuous change in the optical properties of the material under irradiation with a 300 keV electron beam. The plausible physical phenomena leading to these observations are discussed in terms of the homopolar and heteropolar bond dynamics under high energy absorption. The reported phenomena, exhibited by As2S3-thin film, can be crucial for the development of photonics integrated circuits using electron beam irradiation method.

Vectorial FDTD Technique for the Analysis of Optical Second-Harmonic Generation

A vectorial time-domain simulator of integrated optical structures containing second-order nonlinearities has been formulated and tested. The technique is based on the direct time-domain representation of the coupled nonlinear Maxwells equations of the propagating fields. The proposed algorithm accounts for the full optical coefficient tensor, input depletion, and device-wave interactions, where the inaccuracies associated with the scalar and paraxial approximations are avoided. Error analysis associated with the proposed scheme is also given. The proposed model should find application in a wide range of device structures and also in the analysis of short-pulse propagation in second-order nonlinear devices.

A possible approach on optical analogues of gravitational attractors

In this paper we report on the feasibility of light confinement in orbital geodesics on stationary, planar, and centro-symmetric refractive index mappings. Constrained to fabrication and [meta]material limitations, the refractive index, n, has been bounded to the range: 0.8 ≤ n(r[combining arrow]) ≤ 3.5. Mappings are obtained through the inverse problem to the light geodesics equations, considering trappings by generalized orbit conditions defined a priori. Our simulation results show that the above mentioned refractive index distributions trap light in an open orbit manifold, both perennial and temporal, in regards to initial conditions. Moreover, due to their characteristics, these mappings could be advantageous to optical computing and telecommunications, for example, providing an on-demand time delay or optical memories. Furthermore, beyond their practical applications to photonics, these mappings set forth an attractive realm to construct a panoply of celestial mechanics analogies and experiments in the laboratory.

Generation of J 0 -Bessel-Gauss beam by a heterogeneous refractive index map

In this paper, we present the theoretical studies of a refractive index map to implement a Gauss to a J(0)-Bessel-Gauss convertor. We theoretically demonstrate the viability of a device that could be fabricated on a Si/Si(1-y)O(y)/Si(1-x-y)Ge(x)C(y) platform or by photo-refractive media. The proposed device is 200 μm in length and 25 μm in width, and its refractive index varies in controllable steps across the light propagation and transversal directions. The computed conversion efficiency and loss are 90%, and -0.457 dB, respectively. The theoretical results, obtained from the beam conversion efficiency, self-regeneration, and propagation through an opaque obstruction, demonstrate that a two-dimensional (2D) graded index map of the refractive index can be used to transform a Gauss beam into a J(0)-Bessel-Gauss beam. To the best of our knowledge, this is the first demonstration of such beam transformation by means of a 2D index-mapping that is fully integrable in silicon photonics based planar lightwave circuits (PLCs). The concept device is significant for the eventual development of a new array of technologies, such as micro optical tweezers, optical traps, beam reshaping and nonlinear beam diode lasers.

An explicit finite-difference scheme for wave propagation in nonlinear optical structures

In this paper, we present an algorithm that solves a time-domain nonlinear coupled system arising in nonlinear optics. The algorithm is an explicit nonlinear finite-difference method (NFDM) based on the exact solution of the nonlinear discrete equations. It enables simulations that preserve the characteristics of nonlinearity as well as coupling, and can be extended to arbitrary input waveform conditions.

High-frequency time-domain modeling of GaAs FETs using hydrodynamic model coupled with Maxwell's equations

A high frequency full wave model for microwave and millimeter wave GaAs Field Transistors (FET) is presented. The consists of two coupled models for the solid-state and electromagnetic parts of the problem. In the solid-state part, a hydrodynamic model consisting of the conservation equations for carrier density, energy, and momentum is utilized. All the conservation equations are solved with minimum simplifications. On the electromagnetic side, a 3D model consisting of Maxwells equations is used. The time domain simulation of the device is performed using finite difference method. Numerical results of the presented model for a 0.5 /spl mu/m MESFET show that wave effect plays a crucial role in modulating fields and electron velocities inside the active device. The wave propagation is detected and found to cause considerable variations in field distribution and electron velocities.<<ETX>>