Optical homodyne detection

Abstract

This paper contains a theoretical treatment of optical homodyne detection applied both to radiometry and to scattering in the visible and near infra-red, together with some experimental comparisons. A signal estimator, corresponding to the difference in the detector output a.c. power when a given optical field is present or absent, is introduced. The accuracy with which the mean signal intensity can be measured is derived in terms of the inverse root relative variance (IRRV) of this estimator. It is shown that most conventional microwave-based analyses of this problem need revision since they ignore, or treat in an ad hoc manner, both signal fluctuations and photodetection quantum statistics. A rigorous analysis is given including both these effects. The predictions of this analysis compare favourably with existing experimental data. The results are then used to compare signal-intensity measurement by direct or homodyne detection under various operating conditions. Finally, going beyond the measurement of signal-intensity, the probability distributions of the signal estimator are derived and used in an analysis of the performance of optical homodyne systems in threshold signal detection.