Optical phased array receiver with mode diversity and coherent combination

Abstract

Optical phased arrays (OPAs) hold significant promise for low-cost, solid-state beam steering in LiDAR and free-space optical (FSO) communications. The field of view (FOV) is one of the key performance metrics in OPA for both optical beam transmitting (Tx) and receiving (Rx). Currently, people tend to use the same design for both the Tx and Rx parts under the hypothesis of reciprocity. In fact, Tx antennas typically generate well-controlled near-field profiles, whereas Rx apertures encounter randomly distributed incident waves due to uncontrolled reflection and propagation. This work demonstrates that leveraging mode diversity can effectively expand the FOV and enhance the receiving efficiency of Rx OPAs, irrespective of the antenna type. To efficiently utilize collected photons for coherent detection in LiDAR and FSO systems, we introduce an inversely designed mode splitter-converter and a coherent combination architecture. Unlike traditional methods, our approach effectively handles beams with varying amplitudes. As proof of concept, we designed and fabricated an 8-channel edge-emitting OPA receiver operating in TE0 and TE1 modes, employing a sparse array to suppress grating lobes within the ±90° range. Experimental results reveal an FOV of 133° for our multimode receiver, surpassing the 49° FOV of a single-mode counterpart with the same antenna array. Our approach, encompassing both mode diversity and coherent combination, introduces a new degree of freedom – higher-order spatial modes – with the potential to significantly advance OPA receiver design.