This video is taken from the FDE 100 course on Lumerical University.

## Transcript

MODE Solutions supports modelling of linear dispersive materials as well as more complex

materials including nonlinear, spatially-varying refractive index, and anisotropic materials.

The FDE solver, being a frequency-domain solver, does not support any of the nonlinear material

models.

Nonlinear material models in MODE Solutions can only be used with the varFDTD solver.

There are two general types of material models: permittivity models and conductivity models.

Permittivity models are most common.

The type of model that can be used depends on the type of structure.

Most structures are compatible with the permittivity models, while 2D structures (2D rectangle

or polygon) require a conductivity based material model.

Materials are set as a property of a structure object.

Structure primitives have a “material” property with a drop down menu allowing you

to select a material to assign to the object.

For 3D primitives, the material of the object is represented in the simulation by a permittivity.

You can choose to set the material to and specify the refractive

index of the material in the “Index” field.

In the “Index” field, it is possible to type a single number to represent a uniform

isotropic material, or, you can type three values separated by semicolons to represent

diagonal anisotropy where the first value is the refractive index in the x-direction,

the second value is the refractive index in the y-direction, and the third value is the

refractive index in the z-direction.

You can also type an equation as a function of variables x, y, and z to define a refractive

index profile that varies over space.

For example, here we have an equation which sets the refractive index to be a linear function

of x, a sin function along y and a constant along z.

The limitation of the material is that it can only be used to define

a real refractive index that is constant over frequency.

To represent a dispersive material where the index is a function of frequency, you’ll

need to choose a different material from the drop down.

SLIDE: Material property field – 2D For 2D structure primitives (2D rectangle

and 2D polygon), the material of the object is represented in the simulation by a surface

conductivity.

2D structures are used to represent thin films of conductive materials where the film can

be approximated as being infinitely thin.

The material supported for 2D structures is Perfect Electrical Conductor (PEC).

You can also use 2D rectangle structures to represent a lumped RLC load by setting the

material to .

You can then type in the values of resistance (R), impedance (L), and capacitance (C), as

well as a current flow direction, and the structure will effectively represent a load

with a sum in parallel of R, L, and C.

Most imported objects added from the Import drop down menu in the main toolbar use the

Materials drop down menu to set the material of the imported object similarly to 3D structure

primitives, except for the (n,k) Material object.

The (n,k) Material import object is used to specify a 3D object with spatially-varying

refractive index.

This is done by specifying the refractive index (which can be anisotropic) over a 3D

rectangular grid of positions.

Note that this is meant for single frequency simulations only and it cannot be used to

specify a spatially-varying refractive index that is also dispersive.

The material database which can be opened from the Materials button in the main toolbar

includes the full list of materials that you can choose from in the Materials list of an

object and lets you add and edit materials.

The Material Explorer which can be opened from the Check menu in the simulation toolbar

allows you to plot the material data and fit as a function of wavelength or frequency.

In the following subsections the Material Database and Material Explorer will be covered

in more detail.