Guilin Sun
Ansys Employee

It seems you are new to FDTD?

if so, please take some online courses in ALH for paid customers with registration: https://www.ansys.com/services/ansys-learning-hub

there are some open videos online:  https://optics.ansys.com/hc/en-us/sections/360007813194-FDTD100-List-of-videos

You will need to use mode source (usually the first mode, but you need to know which mode to use), PML bcs, Frequency-domain power monitors.

 

You will also need to make sure the length is the grating is "infinitely" over vertical direction, or small such as around 1um.

 

Please try to get some information from the videos and online explanations. If you have questions regarding to source, BCs, monitors please write a separate post for each of them.