Tips for S parameters in a high Q metamaterial in near IR

I want to do S-parameter analysis on my metamaterial that has a periodicity around 1um, and the spectral range is 1um-2um. I want to do S-parameters analysis, and I have put the simulation span, as well as the span of S-analysis to be 2.4um, and it gives me that the monitors are too close. This could be because there are multiple orders. How to check what is the minimum z-span in order to trust the parameters? And, more importantly, since my FDTD simulation region has one end in a glass, how to treat the phase compensation in the S paratemers?
Thanks in advance

Hi Emilija,

These are some comments and suggestions regarding your questions about the S-parameter analysis group:

If the monitor is too close to extract the S parameters directly from the near field, you can increase the span of the analysis group in the propagation direction until the script does not return the warning about the spatial variation. However, if you suspect multiple grating orders then you can use a far-field analysis by enabling the “gratingAnalysis” variable in the analysis script. When this option is enabled only the zeroth grating order is used to find the S parameters.

For the phase correction the S-parameter analysis group assumes that the regions before and after the metamaterial region are filled with homogeneous materials; they don’t have to be the same though. Therefore, if your structure has a semi-infinite layer of glass extending from the metamaterial all the way to one end of the simulation region, it should be OK for the anlysis. However, I am not sure if this is what you meant, maybe you could share your simulation file to get a better idea of the structure and I could provide more specific feedback.

Hope this helps!