How to make FDTD 3D simulations faster

Hello,

at the moment I am simulating multimode interferometers using AlGaAs ridge waveguides. I need to do simulations being up to mm’s long. These take a very long time.
How can I accelerate these simulations?mmi3x3_1500um.fsp (3.5 MB)
Introducing symmetry boundary conditions is not always possible, changing the mesh size is not possible in 2 dimensions because of needed mode confinement.
The best workaround I have found until now is to do 2D simulations and verify the result in 3D, but the outcome is not always comparable.
The file I have uploaded is a(n) (rather extreme concerning simulation volume) example of the kind of simulations I am doing.

Best regards,
Bernhard

Hello @bernhard.unterlechn,

Thank you for the question. There isn’t much you can do to speed up a 3D FDTD simulation except for lowering the mesh density and using symmetry or metal boundary conditions. The 2.5D FDTD solver would probably produce better results than the 2D FDTD solver.

However, I would say the best solution would probably be to use the eigenmode expansion (EME) solver, which scales well with device length and is well suited for MMI couplers. To see how to do this you can take a look at our MMI coupler example.

I hope this helps. Let me know if you have any questions.

Thanks for your reply, I am now trying out the EME solver for these devices.

Unfortunately, the EME Analysis Window crashes every now and then when scrolling. I’m using the 2020a version of the program.

Can you give some more details on what leads to this crash? Also, can you post the simulation file you are using? Thanks.

It always occurs after running the simulation. If the EME Analysis Window is small enough to show scroll bars the whole program stops working when trying to scroll either by directly using the bar or by mouse wheel. Here’s one of my simulation files where this malfunction occurs: mmi_2x2.lms (6.8 MB)

I’m not able to replicate this crash, can you tell me which OS you are using?

As a workaround, I would suggest using a script to perform your simulations and extract your results if the GUI is causing problems. If you’re not sure how to do this, I would recommend taking the online scripting course to learn the basics. Let me know if you have any questions about this.

I am using Windows 10 Enterprise. Now that I resized that window to fit the whole content I can easily circumvent this issue.

I am glad to hear you found a workaround, let me know if you have any other questions!

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