The layer description consists of two lines. The first line is the material sequence of the structure, starting from the
substrate and moving outwards. The second line describes the corresponding film thicknesses.
The format is:
| First Film Material | Second Film Material | Third Film Material | .... | Last Film Material |
| First Film Thickness | Second Film Thickness | Third Film Thickness | .... | Last Film Thickness |
The material names must exist in the refractive index database. This database contains several predefined materials (such as SiO2, MgF2, TiO2 etc..), but users can define their own materials as well. It is also possible to specify a constant index by specifying the material as nXXXjYYY where XXX is the real part of the refractive index and YYY is the imaginary part. If jYYY is omitted, the imaginary part is assumed to be zero. For example, n1.75 will have a constant refractive index of 1.75 for all wavelengths. n1.75j0.05 will have a constant complex refractive index of 1.75+j0.05.
In the second line, layer thicknesses should be defined in nanometers. They can also be defined as a fractional thickness of the reference wavelength. The following notations are allowed:
For example, if the reference wavelength is 650nm, and the film index is 1.75, specifying its thickness as Q will make its thickness equal to 650/1.75/4 = 92.8nm.
Multiple thickness values can be specified for a single layer by enclosing an array of values inside square brackets, such as [100 Q 150]. This will iterate the computation for each value in the array. Only one parameter is allowed to have an array of values. If there are more than one array in the layer description, only the first array will be used, and all subsequent ones will use the first value in that array. If there are multiple incident angles, then the iteration will be done over the angles, and none of the layer thickness arrays will be executed. In that case, only the first values inside the brackets will be used.
Standard thin film notations can be used to describe repeating layers. For example, (MgF2 TiO2 MgF2)^5 followed by (E H E)^5 will repeat five unit cells of (MgF2 TiO2 MgF2), producing a structure with 11 layers.
If there are no layers (i.e., bare substrate), then leave the text box blank.
Example
Si3N4
[Q 90 100]
This structure has only one Si3N4 film. Its thickness values are looped over three values: a quarter wave thickness, 90nm, and 100nm.
Example
Al2O3 MgF2
50.3 140.2
This is a two-layer structure. The first layer on the substrate is a 50.3nm thick Al2O3, and the second layer is a 140.2nm thick MgF2.
Example
(TiO2 SiO2 TiO2)^5
(E Q E)^10
This is a sequence of 10 repeating unit cells of TiO2, SiO2 and TiO2, with thicknesses of an eighth, quarter and eighth of the reference wavelength.
Since the adjacent layers of the same material are effectively merged into a single layer, this is really a 21-layer structure. This type of structure
is typically used as the starting point of a long-pass filter.
Example
n1.87 (GaAs (GaAs AlAs GaAs)^20 GaAs )^2
Q ( E ( E Q E )^20 E )^2
This is a VCSEL cavity enclosed by 20 repeating unit cells on both sides. The layer thicknesses are specified in fractional thicknesses at the reference wavelength. The
first layer is a synthetic material with a fixed refractive index of 1.87.