Hello,
I have a problem that has been already reported in this discussion forum a few years ago with no solution. I report it here https://www.comsol.ch/forum/thread/80041/light-reflectivity-and-transmitivity-of-periodic-surface-structures
In the wave optics model I get high and meaningless fluctuation when I simulate the total reflectance, the 0 order and 1st order diffractions in 2D a grating of 1 um periodicty, 500 nm step width and 150 step height. It looks like the solution does not converge.
I have tried several things: I have increased the PML layers of my structure. rounded off the edges of the step Increased abruptly the mesh size being careful to copy the mesh on the right and left edges of the domain.
What puzzle me most is that I experience the same issue when using the tutorial provided by comsol in the ray optics module called diffraction grating. there I remove the study with the ray optics and consider only the one done with the wave optics. If I increase the size of the step I get fluctuations of the reflectance studies and I don't understand how to solve this.
Anybody willing to help?
Best, Marco