A system has been developed for the purpose of real-time rapid measurement of the optical path difference (OPD) between a reference wavefront and a measuring wavefront of an interferometer by measuring the phase difference between them. The system is capable of measuring accurately OPDs represented by interference patterns with any shape and degree of complexity within the spatial resolution limits of the detector. The interference pattern of the two wavefronts is modulated so that any given point in the interference plane has a sinusoidally varying light intensity with a phase that is proportional to the OPD between the two wavefronts. The individual diodes of an array camera detect the varying light intensity in the interference plane. The output voltage of each diode is digitized and stored. The phase is then computed from these data, and processed to obtain the OPD, peak-to-valley (P-V), and root-mean-square (rms) values of the measured wavefront.