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A powerful waveguide mode solver

The FEM Solver

A finite element mode solver

The FEM Solver brings the finite-element method to FIMMWAVE and is offered as an optional add-on to the FIMMWAVE base module.

 Holey Fibre

Modelling a Holey Fibre: (left and centre) intensity profile of the fundamental mode
and (right) detail of the triangular mesh, showing the effect of automatic refinement at the interfaces. 

Using the FEM Solver you can automatically locate and analyse the eigenmodes of almost any waveguide supported by FIMMWAVE. The FEM Solver is ideal to solve complex waveguide geometries as its highly optimised mesh can adapt itself to virtually any arbitrary shape.

The FEM Solver features automatic mesh refinement techniques which allow it to increase the resolution exactly where it is needed, as shown in the picture above. This will allow you to obtain highly accurate results in a short amount of time.

It will model highly lossy materials and anisotropic materials and will do so rapidly and accurately.

The FEM Solver also supports fully arbitrary dielectric and permeability tensors, enabling the accurate modelling of optically active materials, biaxial materials at arbitrary orientation and magneto-optic materials; this allows the FEM to model optical isolators, PPLN and many others.


Real and complex versions
Bend mode version (see an example here)
Speed and accuracy enhanced for horizontally and/or vertically symmetric structures
Full arbitrary permittivity and permeability tensors
Fast: calculates many modes simultaneously
Mode analysis tools - compute confinement factor, group index, dispersion etc, see utilities.

First and second order elements
High quality, fast fully automatic mesh generator optimised for electro-magnetic problems
Automatic mesh refinement, allowing the solver to deal with high-index contrast, metal and small features very efficiently

The FEM Solver supports perfect electric wall and perfect magnetic wall boundary conditions, as well as perfectly matched layers (PMLs). 

Structures for which the FEM Solver is recommended

Circular or elliptical fibres, photonic-crystal fibres, polarisation maintaining fibers
Waveguides with mixed geometries: rectangles, ellipses, polygons
Waveguide with curved and/or slanted interfaces
Waveguides with both large and very small features

Metallic structures

Uniaxially and biaxially birefringent materials at arbitrary angles
Optically active materials: optical isolators, Faraday rotators etc.
Ferromagnetic, ferroelectric (e.g. PPLN) and magneto-optic materials


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