Passive heterodyning method for dual-beam phase difference measurement and compensation

As a form of interferometric imaging, synthetic aperture optical imaging systems assume a pivotal role in the realm of optical imaging. The optical path difference (OPD) exerts a profound influence on the quality of interferometric imaging outcomes. Nevertheless, existing approaches for optical path correction predominantly rely on mechanical structures for compensation purposes. This paper presents a passive laser heterodyne measurement approach that utilizes a laser as the local oscillator (LO) signal. We have verified that upon the superposition of independent lasers and incoherent broadband light, beat frequency components emerge within the frequency domain. Leveraging the passive heterodyne theory, these components can be efficiently extracted and analyzed. By deploying two passive heterodyne units to detect the identical light source, the optical path difference between the two signals can be ascertained via the cross-correlation function of the two beat frequency signals. Furthermore, digital compensation techniques can be utilized to accomplish precise phase matching between the two light beams. This method surmounts the limitations of conventional dual-beam superposition techniques and puts forward a potential digital correction strategy for the optical path correction of synthetic apertures.