Effect of FDE geometry on waveguide effective and group index

dharmatejapdharmatejap Member Posts: 6


I observed that when FDE width is reduced, I am getting a different (higher) group index. Everything else is same. What is the reason for this and how to arrive at a converged solution? First figure is with a wider (30um) FDE region and second one is 10um.

Best Answer

  • gsungsun Posts: 1,376Ansys Employee
    Accepted Answer

    As you can see from the screenshots, the effective index changes so does the group index, as you can find their relation formula. I am not sure what mesh have you used. Usually FDE does not need very fine mesh. It is also not necessary to set the whole simulation region with the same fine mesh size. I would suggest that you adjust the simulation region and mesh size to reach the fifth decimal digits constant. Further higher accuracy is challenge with too many efforts. The raw material data can be difficult to reach such accuracy.


  • dharmatejapdharmatejap Posts: 12Member


    Thanks for answering.

    Yes, of course, effective index changes and in turn group index changes. My design is a rib waveguide. I added mesh refinement for slab region with 0.01 on x,y and z. Also added another mesh refinement with 0.001 in x, y and z in core region. Now the result stays same between different simulation region widths.

  • gsungsun Posts: 1,376Ansys Employee

    Thank you for your information and I am glad to hear you get good result.

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