It looks like I’m not getting through. OK, let’s take it more slowly, a little bit at a time, line-by-line:
1)OptiGrating cannot calculate the spectrum of a non-uniform grating. It knows the spectra of uniform gratings only.
2) OptiGrating can also calculate the spectrum of two or more gratings connected in sequence.
3) Therefore, when asked to calculate a nonuniform grating, it finds an approximation by dividing the non uniform grating into a specified number of uniform gratings connected in sequence. each of those gratings takes its parameters from the corresponding location on the nonuniform grating.
4) OptiGrating uses scattering matrix theory to combine the spectra of uniform gratings connected in sequence.
5) The number of uniform gratings is specified in the field labelled “Number of Segments” in the dialog box “Grating Definition”. It is user defined because there is a trade-off between simulation time and accuacy. The user makes the most practical choice for each case.
If you follow all of this, I believe I’ve answered your question. If not, can you tell me at what point you are no longer following me?
Regards, Steve