Factors influencing the applications of active heterodyne detection

Abstract Heterodyne efficiency reflects the matching states of phase and amplitude between a local oscillator (LO) beam and a received signal beam and is, therefore, an indicator of system performance. Many factors can cause sensitivity degradation or decoherence in active heterodyne detection applications, such as target speckle, atmospheric turbulence, and optical system aberrations. This paper presents a method for calculating the heterodyne efficiency by mixing LO and customized signal beams in the plane of the detector surface. Results show that the heterodyne efficiency is fixed if the amplitude distribution of the signal light obeys a certain distribution, but the phase mismatches can significantly degrade the system sensitivity. Furthermore, a high-speed camera heterodyne system was developed to evaluate the effectiveness of genetic algorithms for correcting the spatial phase mismatch in applications involving active heterodyne detection. The array detector method improves the heterodyne system sensitivity and benefits active detection applications such as Synthetic Aperture Ladar, Laser Vibrometry, and Long-range Coherent Ladar.