FEEM solver - Simulation object

General tab

• SIMULATION REGION:  Simulation region that the solver will use.

Mesh tab

Global Mesh Constraints

• EDGES PER WAVELENGTH:  The minimum number of edges per wavelength of a triangle (in 2D) used in the mesh.
• REFINE BASED ON MATERIAL PROPERTIES:  If checked (default setting), the effective wavelength in the material (\(  λ_0/n \) ) is used. Otherwise, the solver will use the wavelength of light in vacuum for all material regions.
• POLYNOMIAL ORDER:  Set the order of the basis function in the finite-element solver. A higher order basis function allows to resolve nonlinear variations in the electric field better even with a coarser mesh.

Advanced Options (2D simulations only)

• Geometry Options
  • DEFLECTION TOLERANCE (UM):  Controls how curved surfaces are broken up into multiple linear segments.  A smaller deflection tolerance will force the geometry builder to break up a curved surface into smaller segments.
• Mesh Options
  • TRIANGLE QUALITY: The quality of mesh triangle, defined the minimum angle used in the triangular mesh cells. The higher the angle, the higher the quality of the triangle.

Modal Analysis tab

• SWEEP TYPE:
  • SINGLE: calculates the modes at a single frequency or wavelength.
    - FREQUENCY: the frequency at which the modes are solved for.
    - WAVELENGTH: the wavelength at which the modes are solved for.
• NUMBER OF TRIAL MODES: the number of modes to be calculated.
• SEARCH:
  • NEAR N: Allows you to look for modes near a desired effective index.
    - USE MAX INDEX: Search for modes near the maximum refractive index found in the meshed cross section (real part only).
    - N: Specify the target effective index (complex).
• BENT WAVEGUIDE: This checkbox is used to specify whether the waveguide is bent.
• BEND RADIUS: The radius of curvature of the bend.
• BEND LOCATION: The location of the point used to define the bend radius. Often the center or outer edge of the waveguide. See Solving bent waveguides overview for more information. There are two options:
  • SIMULATION CENTER: The center of the FEEM simulation region, not including the boundary conditions.
  • USER SPECIFIED: The user can select the bend location, using the coordinates BEND LOCATION X, BEND LOCATION Y, and BEND LOCATION Z. A bend location outside of the simulation region plane would be projected in the plane (e.g. a bend location with non-zero Z location would be projected to Z=0 if the simulation region is located on the X-Y plane)

Advanced tab

Global Solver Controls

• MULTITHREADING:  If enabled, the user can choose to divide up and run the simulation over multiple threads.
• AUTO REMOVE PML MODES: When this is checked, un-physical modes that have their energy primarily in the PML are removed and discarded.
• THRESHOLD FOR PML MODE REMOVAL: When PML mode removal is on, modes are discarded if the fraction of the energy in the PML is larger than this threshold.

Results returned

Once the simulation region has been meshed, the FEEM simulation object returns the mesh grid as a dataset that shows the area of the mesh cells, a unique ID of the partitioned regions, and the material index.

After the simulation has been run successfully, the fields and fundamental properties of the calculated modes are returned as unstructured datasets. The FEEM solver returns the result containing the outlined mode properties with frequency/wavelength and the mode number (1, 2, 3...) as parameters:

The modes are sorted based on the complex effective index values according to:

• If the real part of the effective index is larger than the imaginary part, then the modes will be sorted based on descending real part.
• If the real part of the effective index is smaller than its imaginary part, then the modes will be sorted based on ascending imaginary part.

The definitions of the TE polarization fraction, waveguide TE/TM fraction, and effective area used by the FEEM solver are the same as the definitions used by the FDE solver. These definitions, along with more background information on these mode properties, are given on the FDE solver analysis - Mode List and Deck page.

In addition, the FEEM solver returns the unprocessed mode and mesh data as matrix datasets. This data can be used to reconstruct the modes and mesh of the FEEM calculation. The data is relevant to the FEM modeoverlap and modeexpansion script command.