Learning Forum

[Kawshik]

I've simulated a structure using periodic, periodic, PML boundary condition with auto shutoff level 1e-06, min PML layer 12. But i found the reflectance more than 1 for which transmittance also go more than 1. Now how can i solve this problem. In below i've shared my configuration.

[Amrita Pati]

Hi Kawshik,

1. I will recommend you to make sure that the simulation reaches the auto shutoff level at the end of simulation time. You can either check it from the log file. Or check the "status" by clicking on FDTD and then looking at the Results Tab. The status of the simulation should be 2. If not, you will have to increase the simulation
   
2. If the status is 2, and you still see unexpected results, it could be due to reflections from PML. Increase the number of PML layers to 32, 64 etc. and see if the results improve. You can also use the "Steep PML Profile", which is specifically designed to be used with periodic BCs.
   
   

Let me know if none of these work.

Regards,
Amrita

[Kawshik]

I got the status 1. Now, how can i increase the simulation, which you mentioned in yoour reply?

[Kawshik]

Along this problem, I've also found out another problem that the autoshutoff level doesn't decrease from 1 to 1e-06 as long as the simulation proceeds. I actually don't understand where is the main problem here. I'll attach the screenshot of that here. And for that my simulation proceeds to full time.

[Amrita Pati]

Hi Kawshik,

At this point it is hard to say if this is expected or if there is an issue. In some devices, it can take a long time for the energy in the simulation domain to decay. What is the mesh accuracy that you are using? As a starting point I will recommed you to reduce the mesh accuracy to 1 or 2. Then increase the simulation time by 10 times, to see if you are able to reach the auto shutoff level.

Let me know what happens. 

Regards,
Amrita

[Kawshik]

okk, I'll check this