Fourier Transform, Optical Computing, Free Space Optics.
the case N₁ = N₂ = 2​. Then, the input is a square matrix of size two, of the form The FT of this matrix will also be a square matrix of size 2​, given by: (There is no imaginary part because the exponentials are all integer powers of exp(πi), which is equal to -1. The exponential factors are thus