electric field propagation in a bent gradient index WG via FDTD

diedrichdiedrich Member Posts: 1

I'm trying to simulate light propagating in a bent gradient index WG in FDTD. I managed to import the geometry of the WG by importing straight sections of "Spatial (n,k) data" and rotating them. But i just cannot seem to get the light to propagate from one end of the WG to the other end. What usually happens ist that the highest intensity of the E-Field can be observed above the Material and in a straight line away from the source.

Im particularly interested in the propagation loss. Is it possible to simulate this via FDTD? And if so, how do I need to set up my sources so that the light propagates within the WG?

Any help would be much appreciated!


  • kjohnsonkjohnson Posts: 91Ansys Employee

    Hello @Dietrich ,

    Does the waveguide have a circular bend? If it does, instead of using an FDTD simulation to calculate the bend losses you could just use a mode solver. It would be best to use the FDE solver in MODE, but you could also do this with the mode source's eigensolver. You can make the waveguide bent by checking "bent waveguide" (note the geometry in the simulation doesn't have to be bent to do this), then select "user select" and "Select Mode" to go to the mode solver:

    To calculate bend losses, you need to use PML boundary conditions for the mode solver:

    The losses for the modes will then be returned in the mode list results.

    Please let me know if this works for your simulation.

  • diedrichdiedrich Posts: 2Member

    First of all: Thank's a lot for your answer.

    Unfortunately this does not solve my problem since the s-bent WG im trying to simulate follows a sin path.

  • kjohnsonkjohnson Posts: 91Ansys Employee

    Hello @diedrich ,

    You're right, if the curves are following a sin path (or any curved path that doesn't have a constant radius of curvature) then we can't really calculate the bend losses with the bent waveguide solver. Can you please post some screenshots of your simulation geometry (including source, monitors, etc.) and the source edit window? Remember to use the "Add Image" option to place the image directly in your post instead of attaching the image, since Ansys staff can't download files from the ALF.

    For troubleshooting purposes, I would recommend you use an index monitor to check to see if the refracting index was import properly. It's also common to have issues with mode sources, so I would recommend you double check the mode profile being used by the source. You might also want to try replacing the S bend with a straight waveguide to see if that simpler simulation works properly, before moving on to the more complicated S bend simulation.

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