Heterodyne detection of partially coherent optical signal

Abstract

AbstractThe SN ratio is studied for heterodyne detection of partially coherent plane wave optical signals when they are focused by a lens after passing through a circular aperture and are added to a coherent Gaussian beam local oscillator signal. We treat the case in which the intensity distribution of the signal over the aperture is uniform and the natural logarithm of its spatial coherence is expressed as the vth power of the distance between two arbitrary points on the aperture. Using a two‐dimensional Fourier transform, we express the mutual coherence function of the signal on the detector surface in a series form. The results are used to present an expression for the SN ratio suitable for numerical calculations. The SN ratio is investigated numerically with the correlation length on the aperture and the detector radius as parameters. It is found that, regardless of the correlation length, the detector radius of the order of the Airy disk is sufficient for obtaining an SN ratio almost equal to the maximum value determined for each correlation length. We also find that the maximum SN ratio is approached in the case of partially coherent signals if we use the optimum beam parameter of local oscillator signals, which has already been determined.