Reply To: Lumopt: Unable to calculate gradient after changing dielectric constant

[anna.wirth-singh]

Hi Fachien,

Thank you for the response; I'm glad the mesh override helped. To clarify, the most important part of the mesh override is not really to make the mesh finer (one tenth of a wavelength is probably higher resolution than necessary in most cases) but instead it is to force the simulation to use a consistent mesh grid in each simulation. 

That being said, your note that the simulation is successful as 1/3.4 but not 1/3.48 makes me think that the issue is still related to meshing. The reason is, for a high refractive index material (n = 3.48 is quite high), the wavelength of light is much shorter in that material than in the air. So if your wavelength is lambda in air, then it is lambda/n in the medium. Sampling the mesh at lambda/10 is very accurate for the air, but the sampling is effectively much less in the silicon because of the higher refractive index. 

I will get back to you about potential solutions to this problem. The benefit of adaptive meshing is that it automatically samples according to the refractive index to maintain the desired accruacy, but changing the mesh causes issues with lumopt. On the other hand, sampling the entire area at a very fine mesh greatly increases computation time. At the moment, I think that increasing the mesh sampling is the most likely solution.