Effective resolution enhancement of a passive optical phased array using a multi-input star coupler

Abstract Passive optical phased arrays (OPAs) based on the arrayed waveguide grating (AWG) principle enable beam steering without electrical phase shifters and are therefore attractive for low-power solid-state light detection and ranging (LiDAR) systems. However, conventional passive OPAs suffer from a limited number of resolvable points in one steering direction due to the free spectral range imposed by fixed path-length differences between arrayed waveguides. In this work, we propose and demonstrate a resolution enhancement technique for passive OPAs using a multi-input star coupler. By switching the input port of the star coupler, an additional constant phase offset is introduced between adjacent arrayed waveguides through a tilted optical wavefront at the star-coupler output. This phase offset discretely shifts the beam steering origin in the array direction, effectively subdividing the angular spacing defined by the AWG without increasing the wavelength tuning range or employing active phase shifters. A passive OPA with a four-input star coupler and 32 arrayed waveguides was designed and evaluated. Numerical simulations predict an approximately fourfold improvement in angular resolution in the limited steering direction. Experimental measurements of the far-field pattern confirm discrete beam shifts when the input port is switched, validating the proposed resolution enhancement principle. Over a wavelength range from 1480 nm to 1620 nm, the device achieves a field of view of 45° × 15.1°. The total electrical power consumption, including wavelength tuning and input-port switching, is 134 mW, corresponding to approximately 0.065 mW per resolvable point. These results demonstrate that the proposed multi-input star-coupler-based passive OPA provides a practical and power-efficient solution for high-resolution solid-state LiDAR applications.