Mode solver

[Dr. MohammadMahdi Ariannejad]

Dear;
I am using the SOI, and I was wondering why bpm cannot show the mode for SOI, my waveguide I mean channel is 500nm and the height of silicon is 340nm and SiO2 thickness is 1um and 10um in width, therefor within this things so many people got mode and how my design cannot give me any mode?

[Damian Marek]

Hello,

I can find a mode in your design using the FD mode solver. I also upped the number of mesh points to 150 for each dimensions (probably worked with 100 anyways).

Attached is the first mode, which mode solver did you use?

[Dr. MohammadMahdi Ariannejad]

Wow, seriously?
why I do not have FD mode solver? I am using bpm version 11, and I used the ADI mode solver. would you please guide me how to use FD mode in case because I cannot find the FD mode solver!!!! thanks

[Dr. MohammadMahdi Ariannejad]

and one more thing if I run the anlso solve mode it would give me mode!!!
is there anything behind of this?
many thanks
why still I do not have FD! and I do not know why ADI solver cannot solve would you please describe me what is the different between these solvers and which one is better? I want to study about mode solvers many thanks about your help.

[Ravil]

Hi Mohammad,

Although I didn’t have this issue myself, one of my colleagues also faced similar problem. And at the end, as it was shown by Damian, FD mode solver works much better for him in this case!

[Dr. MohammadMahdi Ariannejad]

Dear ravil can you please let me know how to choose FD mode? why I do not have this option

[Damian Marek]

The finite difference mode solver was introduced into OptiBPM 12, unfortunately it is not available in OptiBPM 11.

[Dr. MohammadMahdi Ariannejad]

why I cannot Find FD solver any idea?

[Steve Dods]

“and one more thing if I run the anlso solve mode it would give me mode!!!
is there anything behind of this?”

Yes, there is something behind it. Both the aniso mode solver and the FD mode solver search for modes as eigenvectors in a Krylov subspace using the Implicitly Restarted Arnoldi Method (IRAM). The ADI mode solver, on the other hand, uses BPM with the propagation going in an imaginary direction. The imaginary direction is to promote exponential growth of the fundamental mode (a circular function in the real direction). Imaginary direction BPM would be described, in mathematical terms, as a power method. IRAM is a more sophisticated method than the power method, so it is not surprising that FD and aniso mode solvers can sometimes get it right when ADI gets it wrong.

In fact, this property of the aniso mode solver was noted before we developed the FD mode solver. I guessed the reason for aniso’s success was IRAM, so I developed an isotropic mode solver that uses IRAM instead of imaginary BPM. The result: FD mode solver! Introduced in OptiBPM 12 and found in recent releases of OptiFDTD too!

[Author]

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