Fourier Transform, Optical Computing, Free Space Optics.
the 3D FT of a 3D array A with shape (N₁, N₂, N₃) can be computed in two steps: First, compute the 2D transform along the first two dimensions. This produces N₃ FTs with shape (N₁, N₂). Then compute the 1D transform of the result along the third dimension. This produces N₁ N₂ FTs with size N₃.