Why does the mode loss fluctuate dramatically when reducing the mesh step?

xiaotuxiaotu Member Posts: 1


I am trying to obtain the loss level introduced by a gold(Au) strip in a waveguide. The schemetic diagram is shown in the following.

However, when I reduced the mesh step(from 50nm to 1nm) near the gold(Au) region ('mesh Au'), the simualted loss flucturate dramatically, shown in the above figure. Could you please help to find the causes for loss fluctuation and how to modify my setting to obtain a more accurate loss level? My FDE setting is shown in the following. Thank you so much.


  • kjohnsonkjohnson Ansys Employee Posts: 18

    Hello @xiaotu ,

    A very fine mesh is often required at metal/dielectric interfaces where the field amplitudes rapidly change over a short distance, so it's expected that the results won't converge until the mesh is on the order of nanometers. Have you tried reducing the mesh even further than 1 nm to see if the loss converges? It might help your testing to use metal BCs, so the only loss in the system is due to absorption in the Au and not radiation losses through the GaAs layer into the PML boundaries. You can also speed up your testing by using symmetry boundary conditions on the x min boundary, either anti-symmetric or symmetric, depending on the polarization of the mode you are interested in. Please try that and let me know if it helps.

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