[aifer4]

The Optical Fourier Transform (OFT) in [2] is a way to compute the Discrete Fourier Transform (DFT), and is an alternative to the Fast Fourier Transform (FFT). The OFT basically does a matrix-vector multiplication, where the matrix has a special form, which is accomplished physically using the diffraction of light as it propagates from one plane to another. Although the paper claims constant time for this operation, it’s likely that when the optical array gets bigger, the light has to propagate further for the diffraction pattern to emerge, meaning the time gets longer too. But the coefficient of this scaling is extremely small, because light travels fast. This also accelerates linear algebra using physical dynamics, but can only be used to multiply one particular matrix (the DFT matrix) by an arbitrary vector.