Fourier Transform, Optical Computing, Free Space Optics.
​ nx² independent 1D FTs (one for each line of the input). We will also make use of several sets of integers. For each positive integer n​, we denote by Iₙ​ the set of all integers between ​1 and n​ (included). Let us call A​ the original array. The first step of the Cooley-Tukey algorithm is to