I’m trying to simulate a periodic array of dielectric square patterns and experience spikes at random wavelengths. The spikes show themselves as dips in the reflection spectrum and are usually only 1 datapoint wide. Following suggestions in this forum, I increased the distance of the PML layers from the grating which did not change the shape of the spectrum in any way. The spikes also do not extend below 0 and the simulation converges well.
I was wondering if this might be an artefact from the FFT, but could not find any documentation for such a case. I was hoping someone here could help me. Unfortunately my simulation is part of a confidential project, so I cannot attach the model or the resulting spectrum. I can say however that apart from those spikes the experimental spectrum is well matched.