Practical in-situ beamforming method for optical phased array LiDAR monitoring a single far-field point

Efficient and rapid beamforming methods are essential for calibrating phase errors in optical phased array (OPA) technology, particularly for LiDAR applications. Maintaining a stable beamformed state amidst environmental fluctuations poses a significant challenge, requiring frequent recalibration whenever the state is disrupted. To address this, we propose a practical in-situ beamforming approach utilizing a single photodetector (PD) positioned at the end of the OPA chip to monitor a segment of the reflected light from the included optics. Employing the rotating-element electric-field vector method, we identify initial phase errors on each waveguide channel by analyzing power fluctuations on the PD in response to phase modulation. To validate the proposed beamforming method for its practicality and efficiency, we fabricated a 32-channel OPA device through the monolithic integration of silicon nitride and polymer waveguides. Beamforming was completed within 40 seconds, primarily constrained by data communication speeds. The OPA output exhibited a side mode suppression ratio of -10.7 dB and a horizontal scanning angle of 52°, with the beamformed state remaining stable across the entire scanning range.