Sujeet K. Chaudhuri

The finite-difference vector beam propagation method: analysis and assessment

The newly developed finite-difference vector beam propagation method (FD-VBPM) is analyzed and assessed for application to two-dimensional waveguide structures. The general formulations for the FD-VBPM are derived from the vector wave equations for the electric fields. The stability criteria, the numerical dissipation, and the dispersion of the finite-difference schemes are analyzed by applying the von Neumann method. Important issues regarding the implementation, such as the choice of reference refractive index, the application of numerical boundary conditions, and the use of numerical solution schemes, are discussed. The FD-VBPM is assessed by calculating the attenuation coefficients and the percentage errors of the propagation constants of the TE and TM modes of a step-index slab waveguide. Several salient features of the FD-VBPM are illustrated. >

A finite-difference time-domain method for the design and analysis of guided-wave optical structures

A CAD tool employing the finite-difference time-domain (FDTD) algorithm is developed for the design and analysis of optical waveguide structures. The basic formulation of the algorithm is given, and practical conditions for its application are briefly outlined. The accuracy of the numerical scheme is investigated through a study of a canonical parallel-slabs coupling structure. Both the coupling length and the field distribution are in good agreement with results in the literature. The use of the method is illustrated by an analysis of a directional coupler. >

A hybrid technique based on combining ray tracing and FDTD methods for site-specific modeling of indoor radio wave propagation

The paper presents a hybrid technique based on combining ray tracing and finite-difference time-domain (FDTD) methods for site-specific modeling of indoor radio wave propagation. Ray tracing is used to analyze the wide area and FDTD is used to study areas close to complex discontinuities where ray-based solutions are not sufficiently accurate. The hybrid technique ensures improved accuracy and practicality in terms of computational resources at the same time since FDTD is only applied to a small portion of the entire modeling environment. Examples of applying the method for studying indoor structures and penetration of wave from outdoor to indoor are given at 2.4 GHz. Numerical results are compared with known exact solutions or results of the full wave analysis or traditional ray model to demonstrate the accuracy, efficiency, and robustness of the novel method. Numerical results are also compared with reported measurement results for waves at 1.29 GHz penetrating an external wall with metal-framed windows. Cumulative distributions of field envelope obtained from the hybrid method show close resemblance to the Rayleigh distribution, which conforms to the reported measurement results.

Efficient and accurate vector mode calculations by beam propagation method

An in-depth study of the beam propagation method for the vector mode calculation of optical waveguides is presented. It is established that the imaginary-distance propagation method may be generalized to vectorial modes for arbitrary structures by combining it with the finite-difference vector beam propagation method (FD-VBPM). A simple, unified theory and analysis are developed. An assessment of the accuracy and efficiency is carried out by comparing the simulated results with the analytical solutions for well-known structures. >

A scalar finite-difference time-domain approach to guided-wave optics

A finite-difference time-domain approach that solves the scalar wave equations is proposed and validated. The propagation, reflection, scattering, and radiation of electromagnetic waves in weakly guiding optical devices are described explicitly in the time domain. The method is applied to the simulation of guided-wave devices such as directional couplers and distributed feedback reflectors. A comparison to known analytical solutions shows good agreement.<<ETX>>

A full-vectorial beam propagation method for anisotropic waveguides

An extension of the full-vectorial beam propagation method to anisotropic media is presented. Optical waveguides made of anisotropic materials can be modeled and simulated. The polarization dependence and coupling due to both the material and the geometric effects are considered. >

A True Elliptic-Function Filter Using Triple-Mode Degenerate Cavities

A six-pole triple-mode filter capable of a true elliptic-function response has been synthesized and experimentally realized. This was achieved by using a new intercavity iris structure that can control three intercavity-mode couplings simultaneously.

A finite-difference vector beam propagation method for three-dimensional waveguide structures

A finite-difference vector beam propagation method (FD-VBPM) for three-dimensional waveguide structures is developed. The polarization dependence and coupling of the optical guided-waves in the 3-D structures can be modeled and simulated.<<ETX>>

A semivectorial finite-difference time-domain method (optical guided structure simulation)

A semivectorial finite-difference time-domain method (FDTD) that solves the vector wave equations for the transverse electric fields is presented and validated. By taking into consideration the boundary conditions for the transverse, electric fields in the finite-difference scheme, the polarization effect of the electromagnetic waves can be modeled. In comparison with the full vector FDTD, the present approach requires less memory and is more computational efficient. The method is validated by a comparison with the exact analytical solutions as well as the full vector FDTD results and is shown to be very accurate.<<ETX>>

Simulation and analysis of waveguide based optical integrated circuits

Abstract The employment of single-mode fiber technology, the potentials of coherent optical communication systems, and the novel sensor applications have emphasized the need for integrated optical components, such as couplers, modulators, switches, filters, etc., that are reliable, precise, wavelength selective, and even polarization selective. The design of optimized integrated optical components requires a detailed understanding of the various electromagnetic propagation characteristics of the structures defining the devices. Typical optical structures such as dielectric slab waveguides with junctions, rib waveguides, grating structures, and other dielectric waveguiding geometries could also be made from anisotropic materials, and their properties could be electro-optically altered. In addition to providing optimized design, an accurate method that can simulate the operation of the device allows ways of exploring new concepts. The main objective of this paper is to present the use of these simulation techniques. Three methods for the simulation of the propagation of light through dielectric guiding structures have been considered here. These methods are the finite-difference time-domain (FDTD) method, the coupled-mode theory (CMT) and the beam-propagation method (BPM). The time-explicit FDTD method has been demonstrated to be a very powerful tool in the analysis of arbitrary shaped structures, which may contain abrupt discontinuities in both the propagation and the transverse directions. However, solving an optically long structure by the FDTD method will require a large amount of computer resource. Although the CMT and the BPM are not recommended to analyze a structure with large discontinuities in the propagation direction, they can analyze a long structure very effectively if the transition in the propagation direction is adiabatic. Thus, an optically large (thousands of wavelengths long) structure with bends, junctions, discontinuities, and long guiding structures can be partitioned and solved by a combination of these three techniques. After a review of the various simulation methods for optical circuits, this article focuses on the formulation and the implementation of the FDTD method. Examples are presented on simulations of structures of current practical interest.