FemSIM Product Overview

FEM Generalized Mode Solver

FemSIM™ is a generalized mode solver based on the Finite Element Method (FEM) that can calculate any number of transverse or cavity modes of an arbitrary structure on a non-uniform mesh. FemSIM employs a full-vector implementation and has been enhanced with many features to compute complex modes. The tool is flexible and extendable to a wide range of problems such as high-index contract, plasmonic, and photonic bandgap-based waveguides.

Simulation mesh for aircore photonic crystal fiber


  • Advanced implementation of the FEM algorithm allows for a wide range of simulation and analysis capabilities for different types of devices.
  • Can be used in conjunction with other RSoft tools to solve for modes and then propagate them through a device.
  • Fully integrated into the RSoft CAD Environment.


FemSIM has applications for mode solving to a wide range of integrated and nano-optic devices including, but not limited to:

  • Structures with arbitrary profiles, including those with curved or uncommon shapes
  • Structures with high index contrast and/or small feature sizes
  • Air or solid core photonic fibers
  • Lossy structures
  • Silicon-based devices such as SOIs
  • Polarization rotators
  • Plasmonic waveguides
  • Laser and PBG defect cavities


  • Full-vector analysis for both Cartesian and cylindrical (azimuthally symmetric) structures.
  • Accommodates complex index for lossy materials and high index contrast profiles.
  • Robust meshing scheme which conforms to the index profile using hybrid triangular and rectangular mesh elements.
  • First and second order elements used to avoid spurious modes.
  • PML and symmetric/anti-symmetric boundary conditions.
  • Determination of propagating, leaky, and cavity modes.
  • Higher order modes can be found with minimal additional computational expense.
  • Computation of dispersion diagrams.
  • Output information includes field profiles, propagation constants, overlap integrals, confinement factors, and diagnostics.
  • Automated parametric studies and design optimization using MOST.

Simulation mesh for a rib waveguide with a tilted facet with a highly hybrid polarization both Ex and Ey components of the mode are shown

Application Gallery