Fourier Transform, Optical Computing, Free Space Optics.
separate it into ​nx ny sub-arrays a⁽ʲ ᵏ⁾ with coefficients given by: We then take the 2D FTs of each of these sub-arrays, denoting the results with a ‘​~’. This defines ​nx ny arrays, each of them with shape ​(nx,ny). The third step is where the standard Cooley-Tukey algorithm and the one yielding