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Difference of index between the mode profile and effective index

    • Altair45
      Currently, I investigate the transmission, reflection, effective index, and group velocity in Bragg Grating optical waveguide using the FDTD simulation.
      Before running the simulation, I confirmed the calculated mode and mode profiles in the 'select mode' of Mode Source as the attached image below.
      After the simulation, I confirmed that the max index in the mode profile, attached second image below, was 6.01. But, the calculated effective index was about 2.5.
      Accordingly, I think that the index of the mode profile is the group index.
      I will appreciate your concern to tell the meaning of the difference in the indexes.


    • Guilin Sun
      Ansys Employee


      Somehow the middle figure shows index > 3.4, and the autodetected max index is 3.47175.

      ”Accordingly, I think that the index of the mode profile is the group index.” The first column is the mode number, and the group index is not shown in your case. Maybe you need to upgrade your software:

      Please check the material properties carefully.

      If you want to calculate the group index, you may need to check it here:

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