High-precision beam array scanning system based on Liquid Crystal Optical Phased Array and its zero-order leakage elimination

Abstract

In order to improve the scanning efficiency of lidar, a set of high precision scanning system with 40 × 40 sub-beams is established, in which a liquid crystal optical phased array is used to load the phase calculated by Gerchberg–Saxton(GS) algorithm to split the incident plane wave. Technically, the imperfections of GS algorithm often lead to problems such as sidelobes and uneven intensity of output spots, which eventually result in poor pointing accuracy of sub-beams and low scanning resolution of lidar. To solve those problems, we propose an optical method rather than the classical algorithm optimization methods, which restricts the preset sub-beams to the diffraction limit to unify the actual sub-spot morphology and ensure high pointing accuracy. In this way, the standard deviation of pointing error eventually decreases from 42 μrad to 16 μrad. In the aspect of eliminating zero-order leakage, the zero-order light leakage cannot be separated by the conventional tilt method in the case that the spatial spectrum span of the generated beam array exceeds the cut-off frequency. Concerning this issue, a novel zero-order leakage elimination method is proposed to avoid zero-order leakage by splicing two half beam array of adjacent diffraction orders on both sides of the cut-off frequency. Meanwhile, the intensity correction is carried out to achieve leakage avoidance without damaging the intensity uniformity of the beam array.