FIMMWAVE

The FDM Solver

A finite difference mode solver

FIMMWAVE includes an advanced finite difference mode solver: the FDM Solver. It is implemented in a fully vectorial way. It supports non-uniform meshes, with automatic refinement in regions where higher resolution is needed. Advanced techniques make Photon Design's implementation of the finite difference method substantially more accurate than has been available up until now from this method.

Modes of a hollow waveguide with silver walls. From left to right: intensity, Ex field, Ey field
These modes are highly absorbing and exhibit surface plasmon properties: see how they cling to the metal!

The FDM Solver is very fast on absorbing devices or metallic waveguides for which a complex solver is needed. PML layers are implemented, allowing one to model radiation or leakage.

The FDM Solver is also particularly well suited to model waveguides with high-step refractive index profiles, slanting/curved interfaces and gradient profiles. It is therefore a very good choice for applications in silicon photonics.

It can also be used in its complex version to calculate bend modes.

Features

Fully-vectorial and semi-vectorial versions
Real and complex versions
Uniform and non-uniform mesh, with automatic refinement
User-specified refinement in any area
Bend mode version (see an example here)
Speed and accuracy enhanced for horizontally and/or vertically symmetric structures
Anisotropic waveguides (diagonal tensor)
Fast: calculates many modes simultaneously
Mode analysis tools - compute confinement factor, group index, dispersion etc, see utilities.

The FDM Solver supports perfect electric wall and perfect magnetic wall boundary conditions, Impedance boundary conditions (anywhere between the perfect electric wall and the perfect magnetic wall), Transparent boundary conditions, periodic boundary conditions and Perfectly Matching Layers (PMLs).

Structures for which the FDM Solver is recommended:

High index contrast waveguides.
Bent waveguides.
Waveguides with slanting/curved interfaces.
Waveguides with gradient profiles.
Metallic structures, surface plasmon modes.

See also the Mode Solver Features Table for comparison with other solvers.