How to measure optical channel capacity for an optical system (say 4f optical correlator) assuming a free space propagation, can it be measured using the imaging detector at the output end of the optical system?
I do not know a formal answer to this, but I imagine a good route would be to determine the number of orthogonal channels (pixels or spatial frequencies) and multiply this number by channel capacity for each channel given by the Shannon theorem (I=Blog2(1+S/N) bits). I would use the 2D MTF as the orthogonal channels, using the variation in S/N with spatial frequency - since pixels are not very orthogonal.
I guess though an approximation using pixels would be to calculate the number of resolvable pixels using the Shannon limit given by diffraction and then use a constant SNR for each pixel. But neighbouring pixels are clearly not orthogonal communication channels.
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