Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Question with RF module about system with diffraction
Posted Feb 5, 2017, 2:10 p.m. EST RF & Microwave Engineering 4 Replies
Please login with a confirmed email address before reporting spam
Hi all,
I'm trying to calculate reflection and transmission for a system where (structure attached) we have an periodic (both in x and y direction) system of Si pillars lies in a certain matrix. The periodicity is 400 nm. Light is coming in the z direction perpendicular to the xy-plane. I was using the (user defined) port boundary condition to define the incoming wave and measure the reflection and transmission.
However, the port setting works fine for the spectrum above 400 nm and shows wired wiggles (also attached) for below 400 nm, which is actually the region where diffraction start to make a difference for this system. I was wondering if anyone have seen such kind of problems before and can help me on what's going on and how to correctly simulate these diffractions?
The two labels in the transmission are results using two different automatic mesh where auto_1 is actually the densest auto mesh COMSOL could have so we can't to higher with auto mesh. If anyone have seen this problem and have confirmed that this is indeed something about mesh I may try a denser manually input mesh.
I'll be glad to provide more details about the simulation if needed.
Thanks a lot!
I'm trying to calculate reflection and transmission for a system where (structure attached) we have an periodic (both in x and y direction) system of Si pillars lies in a certain matrix. The periodicity is 400 nm. Light is coming in the z direction perpendicular to the xy-plane. I was using the (user defined) port boundary condition to define the incoming wave and measure the reflection and transmission.
However, the port setting works fine for the spectrum above 400 nm and shows wired wiggles (also attached) for below 400 nm, which is actually the region where diffraction start to make a difference for this system. I was wondering if anyone have seen such kind of problems before and can help me on what's going on and how to correctly simulate these diffractions?
The two labels in the transmission are results using two different automatic mesh where auto_1 is actually the densest auto mesh COMSOL could have so we can't to higher with auto mesh. If anyone have seen this problem and have confirmed that this is indeed something about mesh I may try a denser manually input mesh.
I'll be glad to provide more details about the simulation if needed.
Thanks a lot!
Attachments:
4 Replies Last Post Feb 7, 2017, 6:00 p.m. EST
Please login with a confirmed email address before reporting spam
Posted:
8 years ago
Hi Xiao,
Could you add the dimensions of your setup. Without I can't cancel out what I have in my mind which could be possible or not.
Regards,
Stefan
Could you add the dimensions of your setup. Without I can't cancel out what I have in my mind which could be possible or not.
Regards,
Stefan
Please login with a confirmed email address before reporting spam
Posted:
8 years ago
Hey Stefan,
Thanks for the reply! Sure you mean the dimension of the structure? So the top and bottom layers are air with thickness of 4000 nm. The middle layer is 1000 nm in thickness with the "box" is also air, whose width is 400 nm and with the pillar is silicon whose radius is 100 nm. The excitation port is on the top and the other port is at the bottom. Periodic boundary condition has been applied to all of the side boundaries.
What do you have in mind that may cause the problem? Thanks a lot for the help on this!
Best!
Xiao
Thanks for the reply! Sure you mean the dimension of the structure? So the top and bottom layers are air with thickness of 4000 nm. The middle layer is 1000 nm in thickness with the "box" is also air, whose width is 400 nm and with the pillar is silicon whose radius is 100 nm. The excitation port is on the top and the other port is at the bottom. Periodic boundary condition has been applied to all of the side boundaries.
What do you have in mind that may cause the problem? Thanks a lot for the help on this!
Best!
Xiao
Please login with a confirmed email address before reporting spam
Posted:
8 years ago
Hi Xiao,
Maybe it is a problem with the wall condition of the periodic structure. What if you expand your box e.g 800nm width and four wires? If you get sensible results than it could be that you had waveguide modes from the walls. But I am not sure because I didn't use periodic structures in Comsol yet.
Maybe it is a problem with the wall condition of the periodic structure. What if you expand your box e.g 800nm width and four wires? If you get sensible results than it could be that you had waveguide modes from the walls. But I am not sure because I didn't use periodic structures in Comsol yet.
Please login with a confirmed email address before reporting spam
Posted:
8 years ago
Hey Stefan,
Thanks for the suggestion. Actually that's exactly what we are testing right now. I think I also found that for these systems with diffraction, I may need to use periodic port setting but I haven't figured out how to get that to work yet. But anyway thanks a lot for the help.
Best!
Xiao
Thanks for the suggestion. Actually that's exactly what we are testing right now. I think I also found that for these systems with diffraction, I may need to use periodic port setting but I haven't figured out how to get that to work yet. But anyway thanks a lot for the help.
Best!
Xiao