Husain M. Masoudi

Modeling second-order nonlinear effects in optical waveguides using a parallel-processing beam propagation method

In this work, we present a simple efficient numerical solution for the three-dimensional coupled wave equations containing a second-order nonlinearity, using an explicit finite difference beam propagation method (EFD BPM). The linear EFD-BPM is known to be very efficient and to gain large speed up when implemented on parallel computers. The new nonlinear version of the EFD-BPM has the same features of the linear counterpart in using two separate computational windows, one for the fundamental field and the other for the second-harmonic field. We demonstrate the implementation and discuss the application of this method to a nonlinear rib waveguide using the quasi-phase-matching technique.

Efficient time-domain beam-propagation method for modeling integrated optical devices

A new efficient technique that models the behavior of pulsed optical beams in homogenous medium, metallic and dielectric waveguides, is introduced and verified using both linear nondispersive and dispersive examples that have analytical predictions. Excellent accuracy results have been observed. The method is called time-domain beam-propagation method (TD-BPM) because it is similar to the classical continuous-wave BPM with additional time dependence. The explicit finite difference and the Du Fort-Frankel approaches were used to discretize the TD-BPM equation. Comparisons between these techniques are also given with the application of the perfectly matched layers as spatial boundary conditions to the Du Fort-Frankel. Then the TD-BPM was successfully applied to model a two-dimensional dielectric Y-junction. It is concluded that the new technique is more efficient than the traditional finite-difference TD method, especially in modeling large optical devices.

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.

Parallel beam propagation method for the analysis of second harmonic generation

We extend the linear parallel explicit finite difference beam propagation method to model the nonlinear second harmonic generation process in three-dimensional waveguides. It has been concluded from testing this method that it is accurate as well as very efficient.<<ETX>>

Parallel beam propagation methods

We have implemented two explicit finite-difference beam propagation methods on a transputer array for analyzing three-dimensional optical semiconductor devices. Both methods, in their parallel form, can execute, per propagational step, a large problem that contains 10/sup 6/ discretization points in a few seconds. We compare the speed of the transputer implementations to the speed of connection machine implementation of the same methods.<<ETX>>

A Novel Nonparaxial Time-Domain Beam-Propagation Method for Modeling Ultrashort Pulses in Optical Structures

In this paper, a new nonparaxial time-domain beam-propagation method (TD-BPM) based on Pade approximant for modeling ultrashort optical pulses has been proposed and verified. The high efficiency of the technique in modeling long device interaction comes from solving the TD wave equation along one direction and allowing the time window to follow the evolution of the pulse. The accuracy of the method was tested in three different environments of homogenous and nondispersive medium, metallic, and dielectric waveguides and then was applied to model ultrashort pulse propagation in a directional-coupler device. The characterization of the technique shows excellent performance in terms of accuracy, efficiency, and stability, which the conventional paraxial TD-BPM failed to achieve. The new TD-BPM is particularly well suited for the study of unidirectional propagation of compact ultrashort temporal pulses over long distances in waveguide structures. [All rights reserved Elsevier].

Time-domain finite-difference beam propagation method

A new technique to model the behavior of pulsed optical beams in waveguides is proposed and analyzed. The technique is an extension of the traditional continuous-wave beam propagation method (BPNI) to include time dependence, therefore called the time-domain BPM (TD-BPM). The method was tested using different waveguide examples and it is concluded that the technique is simple and accurate. Compared with the finite-difference TD method, the new TD-BPM is more efficient in terms of computer memory and execution time especially for large optical devices.

Efficient Iterative Time-Domain Beam Propagation Methods for Ultra Short Pulse Propagation: Analysis and Assessment

The time-domain beam propagation method (TD-BPM) has been implemented and analyzed using several iterative numerical techniques to model the propagation of ultra short pulses in optical structures. The methods depend on one-way non-paraxial time domain propagation that use Pade approximant formulation. Several numerical tests showed that the iterative TD-BPM techniques are very stable and converge using few iterations. From accuracy assessment compared to the FDTD, it has been observed that the longitudinal and the temporal steps sizes can be a number of orders of magnitude larger than the FDTD step sizes with little percentage difference. Computer performance analysis showed the TD-BPM is well suited for long dielectric structures interaction of short and ultra short pulse propagation.

Spurious modes in the DuFort-Frankel finite-difference beam propagation method

In this letter, we analyze the DuFort-Frankel beam propagation method (BPM) which is a modification to the known explicit finite-difference beam propagation method (EFD-BPM) and found that there are some precautions that must he taken before using the method. The accuracy and the efficiency of this method has been shown and compared with the most popular FD-BPMs.

A Stable Time-Domain Beam Propagation Method for Modeling Ultrashort Optical Pulses

A new technique to model ultrashort optical pulses is proposed and verified. The technique uses Pade approximant to account for the fast pulse propagational variations. Numerical parameters of the technique have been tested and it was shown that the method is simple, very stable, and accurate in modeling ultrashort optical pulses in long propagation interaction