Limitations of fringe-parameter estimation at low light levels*

Abstract

Fundamental limitations of estimating the amplitudes and phases of interference fringes at low light levels are determined by the finite number of photoevents registered in the measurement. By modeling the receiver as a spatial array of photon-counting detectors, results are obtained that permit specification of the minimum number of photoevents required for estimation of fringe parameters to a given accuracy. Both a discrete Fourier-transform estimator and an optimum joint maximum-likelihood estimator are considered. In addition, the Cramér–Rao statistical error bounds are derived, specifying the limiting performance of all unbiased estimators in terms of the collected light flux. The performance of the spatial sampling receiver is compared with that of an alternate technique for fringe-parameter estimation that uses a barred grid and temporal sampling of a moving fringe.