Optical phase measurement in real time

A method has been developed for the real-time measurement of optical phase. The optical wave whose phase is to be measured is interfered with a spatially coherent plane-wave reference on the face of a photodetector array. The irradiance is measured simultaneously at all array elements for each of three specific phase shifts of the reference, and the phase and magnitude at each array element are calculated from the three measured irradiances by a simple algorithm. The method can be used for hybrid optical-digital analog computation of 2-D Fourier transforms: information is introduced coherently into the front focal plane of a lens with a spatial light modulator, and the phase and magnitude are measured in the back focal plane. Experimental results of the Fourier transform technique are described.