Learning Forum

[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:https://optics.ansys.com/hc/en-us/articles/360041567754 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);
imagesc(abs(fftshift(Y))),

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]

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