some questions about the EDG device

dear all
Recently I have learnt the etched diffraction grating(EDG)with the Bragg structure and I have built the model by using varFDTD.But when I run the programm,I found the transmission of the output is too low.I doubt whether I have set something wrong with my programm.Can you help me check it.Thanks in advance.
1.lms (514.7 KB)

Hi, @jbwei

I wonder is the grating parameters have been thoroughly calculated by somewhere or it is entirely your try?
If the first, could you provide more information.

P.S.: I am running your script and this seems to take quite a time.

I mentioned that in the position of the point that used to calculate the mode profiles is out of the simulation region.
Change the position to a proper one in the VarFDTD - > Effective index -> Slab mode position.
Otherwise the input field does not even enter the grating body.
I simulated the device with coarser mesh and the transmission obtained was much better (~5-10%) than used to be with incorrect point.
Try simulation once again this way.

dear msaygin
In fact you can have found that I built the model by inserting the GDS file. The structure of EDG have been simulated by theoretical calculation and the result of the varFDTD must be wrong.
I will have a try as your guidance of the second reply.Thanks.

dear msaygin
I have a try by change slab mode position to a proper one ,but the transmission of the output is still very low.I dont know how to modify the simulation programm.Do you have any other idea to modify the programm.
Hope to get your feedback. Thanks in advance.


I would first simulate the structure with the frequency monitor that occupy it all.
Doing this, it is more convenient to look at the field distribution in case of anything going wrong.

By the way, why do you use 4-micron-wide waveguide? It is multimode and the input bend generally maps it into a mixure of higher-order ones.

P.S.: I am having some troubles with my computer and can not run simulations. Try to simulate just the first bend before the grating body.