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MZI modelling

    • Chinna Devarapu

      Hi everyone, I have some problems in the simulation results of a symmetric mach zehnder interferometer.
      It seems that the results change in base of the order in which I define the components or I put the output monitor, that's is very strange. 
      As I expect from theory, a symmetric MZI must be with output almost flat without fringes, really I have these.

      General settings are: varFDTD2.5, PML boundaries with anty-symmetry in ymin and silicon nitride Kishkat model as guided medium taking into account a thickness of 0.3um and width of the components 1um.

      First configuration:
      XY plane mzi4test

      in the two monitors after the MZI arms I have exactly 49 percent in both so seems that the splitter bezier works properly.

      If I change the position of monitor,near the more white part, I have:

      another point also if I change the order of definition of the components..but still fringes are avoided only in this last case sent.
      I can't find the reason why it happens.

      I already checked the index and the different simulation time of the varFDTD but it isn't the problem.


      I hope you can help me in finding the mistake, thank you in advance.

    • Guilin Sun
      Ansys Employee

      "the results change in base of the order in which I define the components ", if the geometries have overlap, then the result may change: by default they have the same mesh order. then the last geometry that is added has higher priority than the previously added geometry. Please refer to this article:

      to avoid this, you can modify the mesh order.

      The order of monitors, or the order of geometry and monitors should not matter. Please use an index monitor to check if the configuration is what you expect. 


      The screenshots and questions you posted later seem to be that, the posiztion of the monitor change the transmission? it mighe be due to mesh, if the monitor is about the same size, larger than the waveguide. Also make sure there is no radiation modes. You can use field monitor to check the field intensity, with log scale.





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