Development and Applications of Finite-Element Time-Domain Beam Propagation Method
|Keywords:||有限元素法;光波導分析;時域分析;時域波束傳播法;finite-element method (FEM);optical waveguide analysis;time-domain analysis;time-domain beam propagation method (TD-BPM)||Issue Date:||2005||Abstract:||
Traditionally, the beam propagation method (BPM) assumes only the forward propagating waves exist. It is difficult to take into account backward reflecting waves in the BPM. In this research, a time-domain beam propagation method (BPM) based on the finite-element scheme is described for the analysis of non-forward-propagating pulses of both transverse-electric and transverse-magnetic modes in waveguiding structures containing arbitrarily shaped discontinuities. In order to avoid nonphysical reflections from the computational window edges, the perfectly matched layer boundary condition is employed. The present algorithms use two kinds of approximations, the paraxial approximation and the Pade approximation, which can treat the narrow-band and the wide-band optical pulses, respectively. After validating this method for a simple slab waveguide and an optical grating with modulated refractive indexes, various optical waveguide structures, such as the bent waveguides, and the microcavity ring and disk resonators are simulated. The calculated results show that the Pade approximation can successful simulate a short pulse with only several femtoseconds. Besides, the method is employed to study several two-dimensional high-index-contrast 90-degree waveguide bend structures previously reported in the literature regarding their TE mode propagation characteristics. The device structures considered include the simple 90-degree-bend waveguide, the 90-degree-bend waveguide modified by a square resonator, the 90-degree-bend waveguide with a 45-degree-cut at its outer corner, and the 90-degree-bend waveguide modified by a quarter disk. The waveguide structure is assumed to have the core width of 0.2μm, the core index of 3.2, and the cladding index of 1.0, and the wavelength range is from 1.48μm to 1.62μm. By adding some resonator structure at the waveguide bend, the transmittance performance can be significantly improved. We also show that there are some differences in the numerical results compared with those calculated by using the finite-difference time-domain method for the 90-degree-bend waveguide with a 45-degree-cut at its outer corner and the 90-degree-bend waveguide modified by a quarter disk which have the curved/oblique shaped dielectric interfaces.
|Appears in Collections:||光電工程學研究所|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.