What is the best practice to check FDE convergence?

    • mukundsingh

      I am simulating a SOI waveguide in Lumerical FDE.


      1) When I change the FDE size, the number of propagating modes change. How to decide which size is best and accurate to the realistic operation of the device?

      2) Also, when testing the fabricated waveguide, does the laser beam spot size has to be similar to the FDE size?


      PS: I am trying to write a lumerical script for it using for loop. Is there a better/simpler way to do it using GUI?

      Thank you.

      Best Regards.

    • Guilin Sun
      Ansys Employee

      For question 1, I guess you used the default Metal boundary condition. So it is normal to have more number of modes in larger box (think it as a metal box partially filled with waveguide materials). But they do not affect the mode you desire. Most often, customers are only interested in the guided modes, or the fundamental mode, which needs to be identified, regardless all other higher "modes".  The FDE size should be ok, as long as the mode is not truncated to certain degree. You can view the mode amplitude in log scale and check the magnitude at the boundaries.

      for question 2, it all depends on what you want to do. If you want to get the best coupling from actual beam to the waveguide, you will need to know the experimental beam property, say the beam waist. Most often it is the laser beam passing through a microscope objective, with certain numerical aperture NA. Once you know the NA, or beam waist on the waveguide to be coupled, you can create a Gaussian beam from the GUI.


      NA beam

      Scalar beam:


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