The solvers currently implemented in FIMMWAVE are:

The FMM Solver. This solver, based on the mode matching method, is optimised for rectangular waveguide structures. It is fully vectorial, and there is either a generic version capable of solving structures with complex refractive index (such as metallic components and waveguides with gain), or a version optimized for real structures only. 

The Mode Matching Method models an arbitrary waveguide by a list of vertical slices, each uniform laterally, but composed vertically of a number of  layers. A 3D mode is built up from the TE and TM 2D modes of each slice. The method is theoretically exact for an infinite number of 2D modes. The modelled area may be bound by either perfect metallic or magnetic walls or with periodic boundary conditions. The method will happily deal with modes that are near cutoff in the lateral direction, without loss of accuracy or an increase in computation time. Such modes cannot be modelled accurately with finite element or finite difference methods. 

Speed: locating the zero order mode of a 4-slice ridge structure with a resolution of 30 2D modes will take about 2s on a 2GHz Pentium IV using the Molab (see below). If you had some idea of where it is, it might take 1s and regenerating it from an accurate eigenvalue will take a fraction of a second. The calculation time is proportional to the number of slices in your structure.

Effective Index Solver: This well known approximate method is both a fast and reliable way of finding estimates for 3D modes for near 2D waveguides (many ridge structures fit into this category). The solver  uses our home grown 2D solver (also used in the FMM solver) which makes it extremely robust. In particular it can deal with structures with completely decoupled cores. 
General Fibre Solver (Opt 06): This is a fully vectorial solver for generic circular waveguides with arbitrary refractive index. It will find all the modes of such structures using metallic or transparent boundaries. Although it is a fully vectorial solver it exploits the circular symmetry, thus making it extremely fast. A scalar version is also included.

Gaussian Mode Fibre Solver (Opt 06): This is a quick utility for getting the fundamental mode using the gaussian approximation. The user simply specifies the effective index and the spot size of the desired mode - useful where the fibre profile is not known.