Reg: simulation region FDTD



Respected Sir,

I am new to lumerical FDTD simulations. For any Bragg grating setup the substrate dimension is taken as in few hundreds of micrometer. In this case should i include this complete region for my simulation, or i can just take my interesting space. Here i attached two cases, please help me in this regard.

Simulation_region_case1.fsp (292.0 KB)
Simulation_region_case2.fsp (391.9 KB)

Thank you


Hi. you should enter the one period of your bragg grating in the simulation region. and in the FDTD boundary condition you should enter the “periodic” boundary condition for your region.



thank you for the reply and information, more on that i have one more doubt, if you check my sample cases, the FDTD y -axis region i have provided two lengths one is fully covering my Si substrate the other not, which one would be better?

Thank you


Hi @kanchana

I guess you inquiry was mainly in regard to y-min value of FDTD simulation region. We recommend leaving at least half distance between edge of critical objects and PML boundaries. In your case since the light that gets into substrate will be finally absorbed, you can bring the y-min of simulation region closer as is shown below:

If you are new to Lumerical, I recommend to taking the free online course and reviewing the application example below:
Lumerical University


Thank you for the support sir