Fourier transform of field distribution of L3 cavity

    • Jiahui Huang

      Hello, I have a problem with the results of doing Fourier transform of the field distribution of a L3 cavity. The starting example I use is: and I change the cavity to a L3 cavity and obtain the field distribution of the fundamental mode from the mode monitor as below:

      and if I use log scale on the field magnitude, I notice that there is finite field at the edge

      Then I apply the 2D Fourier transform in Matlab using

      Y = fft2(X);

      where X is the field distribution of above image.

      I got the below result and I think the center bringth region is an artifact from the Fourier transfrom of a rectangle due to the finite field magnitude on the edge (see field distribution in log scale mentioned above):

      Then I decide to increase the amount of holes so that the field decays sufficiently on the edge and the resulting field distribution in log scale is below:

      And you can see that the field decays to smaller values on edge thanks to increased amount of holes. However when I do Fourier transform on this one, I still obtained a center bright region with even larger value

      I would appreciate if you have any comments on how to get rid of the center bright region!

    • Guilin Sun
      Ansys Employee

      Fourier transform requires the field intensity to be zero at the monitor edge. You will need to smoth the field data. Please refer this example: Equi-frequency contours of photonic crystal 


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