Hi, Thank you so much for your quick reply! The figure below shows the structure of my 2D sinusoidal grating. The periods along the x and y directions are 8 microns. The index of my material at 550 nm is 1.62, while the background index is 1.47. There is a 10 microns thick layer below the 2D grating structure. Since I want to see the reflection and transmission in the background index, my current FDTD region is 8 um * 8 um * 14 um. The BC along x and y directions are bloch, the BC at z and -z directions are PML. I have 2 questions:
  1. Because the entire thick layer is included in the FDTD region, the simulation time will be very long. Do you have an equivalent method to replace this 10 microns thick layer in order to save simulation time?
  2. Since I need to do the simulation at oblique incidence, will the above equivalent way still be effective at oblique incidence?
I really appreciate your time and help!
structure schematic.png