We have been using Lumericals in the past year to simulate photonic crystal devices, but recently we notices that we are unable to reproduce meaningful results. As an example I have attached two simulation files:
FSP File1: Source oriented in x y z are placed on top of a silicon substrate, source emit at 1.13 micron, monitor above the source records the power spectrum in the z direction
FSP File2: Same as file 1 except a SiO2 layer of quarter wavelength lamda/4n is inserted on top of silicon, designed to have a Bragg reflection at the boundary and constructive interference at the design wavelength of 1.13 micron.
The images have the monitor’s power measurement in Visualizer 1 and the source power in visualiser 2. We notice the following observations that do not make sense:
monitor transmission produces a sloped line, We know from an earlier post that this is because there is a normalization with the source power, but why does the slop change sign when we add a silicon dioxide layer?
Looking at lamda=1.13 on visualizer 1 in both images, The design with bragg reflection (source on SiO2/Si) shows T=0.15 whereas without bragg reflection (Source on Silicon directly) T=0.185! Lumerical seem to tell us that the Bragg reflection does not work!
I am sure there’s something wrong with our simulation parameters but we can’t figure out what that might be, we have tried a lot of different simulations with SiO2/Si that does not seem to make sense at all.
Please help us figure out what the problem is,