Stress Solver

The Stress Solver for FIMMWAVE allows the FIMMWAVE user to calculate the stress fields in a waveguide and the consequential perturbation of the waveguide modes. The Solver supports thermally-induced stress fields – typically generated during cooling of a device constructed from materials with different thermal expansion coefficients. The model is a two dimensional model based on the plane strain assumption The device is considered to be long along its z axis in comparison to it’s cross section and the strain in the device along the z axis is considered to be zero. The Solver is based on the finite element method.

The Solver operation is straight forward – the user enters thermal expansion coefficients, Poisson’s ratio, Young’s modulus data and the photo-elastic constants for each material in the device, via the usual FIMMWAVE Material Database. The user then enters two temperatures – the first temperature at which the device is assumed to be at zero stress, and the second usually lower one, the temperature at which the stress calculation is desired.

• 2D-FEM based algorithm, with automatic mesh generation
• Fully integrated with FIMMWAVE waveguide definition interfaces – so users can calculate stresses on RWG, MWG or FWG waveguides.
• Support for stress-induced birefringence coefficients, to determine the perturbation of the waveguide refractive index due to stress. The output is a diagonal dielectric tensor.
• All FIMMWAVE mode solvers may be used on the resulting stressed waveguide to calculate the waveguide modes; the FDM and FEM Solvers support an arbitrary diagonal permittivity tensor.

• Modelling of multicore and PANDA fibres – circular stress-inducing elements create birefringence in the optical fibre.
• SOI waveguides – calculate the stress on an SOI waveguide due to manufacture cooling and the differential thermal expansion of silica and silicon.