Introduction to OptiBPM

OptiBPM is a powerful, user-friendly software system that enables you to create designs for a variety of integrated and fiber optics guided wave problems on your computer. Beam Propagation Method (BPM) is a step-by-step method of simulating the passage of light through any waveguiding medium. An optical field can be tracked at any point as it propagates along a guiding structure in integrated and fiber optics. BPM allows computer-simulated observation of the light field distribution. You can examine the radiation and the guided field simultaneously. OptiBPM provides easy data entry for laying out waveguide devices. The layout environment contains waveguide blocks called primitives. You can design devices easily and configure various simulations. The graphical project layout is a user-friendly graphical interface for designing photonic devices. Designing tools are provided in toolbars and menu options. The tools include waveguide primitives, editing and manipulation tools, and special layout regions.

The OptiBPM program simulates light propagation in two-dimensional (2D) and three- dimensional (3D) waveguide devices.

The 2D dimensions are:

•     X-direction (vertical)—Transverse

•     Z-direction (horizontal)—Propagation

The 3D dimensions are:

•     X-direction (vertical)—Transverse

•     Y-direction—Depth

•     Z-direction (horizontal)—Propagation

Note: The simulated devices have a step-like effective refractive index distribution in the transverse dimension.

To obtain a 2D device from a real 3D device, apply the effective index method. The reduction from 3D to 2D consists of replacing the two-dimensional transverse cross- section of the device with a one-dimensional cross-section. The actual index cross- section is replaced by a one-dimensional effective index distribution. Although the effective index method is an approximate solution, it works for many devices.

BPM 3D provides all the tools you need for step-index waveguide design. In BPM 3D, the entry modeling data consists of the refractive index distribution, the starting propagation field, and a set of numerical parameters. The index of refraction distribution is provided by the waveguide structure laid out in the project layout. The starting field can be a waveguide mode, a Gaussian field, a rectangular field, or a user-defined field supplied from a file. The starting field and other simulation parameters are specified in the Global Data dialog box that is accessed through the Simulation menu. Output data consists of different files that can be displayed or used for other simulations.

Numerical Simulations

The OptiBPM processing environment contains the Beam Propagation Method (BPM) as its core element, as well as mode solvers that are compatible with the BPM algorithms. BPM is based on a numerical solution of equations that govern light propagation in dielectric media. BPM considers monochromatic signals and is related to solving the Helmholtz equation. Models of propagation based on approximations of the Helmholtz equation are used to:

•     simplify the simulations

•     reduce the processing time

•     manage computer memory better

 

 

2D BPM

The 2D BPM simulator is based on the unconditionally stable finite difference method algorithm of Crank-Nicolson. You can customize the following program options, depending on the design:

•     Algorithms giving a choice between TE and TM polarization

•     Wide-angle propagation based on Padé approximants, Padé (1,1) and Padé (2,2) up to Padé (4,4)

•     Starting field choice as a waveguide mode, a Gaussian field, a rectangular field, or a user field

•     Starting field can be launched at an angle

•     Reference refractive index choice as modal, average, or user-defined

•     Simple or full transparent boundary condition (TBC)

 

 

3D BPM

The full 3D BPM simulator is based on:

•     The Alternating Direction Implicit (ADI) scheme

•     Scalar algorithms

•     Semi–Vector algorithms giving a choice between quasi-TE and quasi-TM polarization

•     Full–Vector algorithms governing both transversal field components

 

 

Scan parameters automatically

The designer’s goal is to achieve the optimum device performance. To find the optimum conditions, you often need to repeat the simulations with different design parameters. OptiBPM enables you to perform automatic, loop-like calculations called parameter scan calculations. The program names the result data files sequentially and saves the files.

 

 

Mode solvers

In OptiBPM, the mode solvers are compatible with the 2D and 3D BPM algorithm. The solvers employ different methods:

•     Transfer Matrix Method (TMM) in 2D for multi-layer planar structures,

•     Alternating Direction Implicit (ADI) method in 3D

•     Correlation Function Method (CFM) in 2D and 3D

The program for planar structures is based on resolving multiple boundary conditions at dielectric interfaces between layers. During propagation of a user-defined field, the CFM calculates the correlation integral between the input field and the propagating field at every point. This creates the field amplitude correlation function for the waveguide. The correlation function provides all the information required for a complete modal description of the fields, including:

•     propagation constants

•     weights of each mode

•     mode eigenfunctions

The ADI method separates the X and Y derivatives into two parts of one iteration step. This method is superior to other finite-difference techniques because of its fast convergence. The ADI method also provides all propagation constants and mode eigenfunctions.

Graphics

OptiBPM has state-of-the-art graphics that enable you to view, manipulate, and print field amplitude, phase, effective index distribution, and other calculated data.

The graphical features include:

•     Topographical view of the 3D graphs

•     Color height coding

•     Solid modeling in 3D graphics

•     Adding customizable colors

A monitoring window allows you to track the signal along selected multiple paths in the waveguide circuit.