Advanced Capabilities in Ansys Lumerical FDTD — Lesson 5

Anisotropy

As we saw in the previous units, it’s possible to specify the diagonal anisotropy of materials.

For the <Object defined dielectric> material

In the material database

The grid attributes listed below can be used to represent more complex anisotropy.

Permittivity rotation grid attribute

Used to rotate the permittivity tensor by given Euler angles.

LC orientation grid attribute

Set the orientation of the extraordinary index of a liquid crystal.

Matrix transform grid attribute

Used to apply a unitary transform. This can be used to represent a permittivity tensor with off-diagonal components.

Index Perturbation

The local change in the refractive index of a material due to variations in charge carrier density or temperature can be simulated using the index perturbation material model together with the np density and/or temperature grid attributes.

The index perturbation material model:

An index perturbation material should be added for each different material whose refractive index should change as a function of charge carrier density or temperature. The model used to relate the change in refractive index to carrier density and temperature is specified in the material model.

np density grid attribute
The np density grid attribute imports the charge carrier density profile over space from a prior simulation using the CHARGE solver.

Temperature grid attribute
The temperature grid attribute imports the temperature profile over space from a prior simulation using the HEAT solver.

Material Plugin Framework

A material plugin framework is available which allows advanced users to create their own material models by coding them using C++ and compiling them as plugins that can be added to the materials database.

Users must be able to specify the material polarization update as described here.

Note: This is an advanced feature because the update equations are defined by the user, so the models may not necessarily be stable or accurately represent physical behaviors. Users must understand the models and their limitations.

The link to the demonstration video of generating a new material plugin is available in the Related Links.