Photonics

Photonics

negative loss for light propagation in

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    • diedrich
      Subscriber

      Im trying to get radiative loss for WGs with a refractive index distribution that I define via a n-k-material model.

      For the n-k-material model I can only define the real part of the refractive index. I use PML-boundaries.


      For some reason the second mode has a negative loss, no matter which simulation parameters (mesh-grading, simulation area) I choose.

    • Guilin Sun
      Ansys Employee
      Since your material is lossless, this negative imaginary part is due to numerical calculation error, which is already very small, 13 orders smaller than the real part. You can ignore it. Or you can use Metal BCs. When PML is used, and the material has no loss, the calculated beta and thus effective index will always have imaginary part, which can be positive or negative, from numerical errors.
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