  Optical phased array (OPA) is a promising beam-steering device for various
applications such as light detection and ranging (LiDAR), optical projection,
free-space optical communication and switching. However, the previously
reported OPAs suffer from either an insufficiently small number of resolvable
points, or a complicated control requirement due to an extremely large number
of phase shifters. This work introduces a novel array configuration for OPA
devices based on the non-redundant array (NRA) concept. Based on this design,
we can realize high-resolution OPA whose number of resolvable points scales
with N2. In contrast, that of traditional OPAs scales only with N. Thus, a
significant reduction in the number of required phase shifters can be attained
without sacrificing the number of resolvable points. We first investigate the
impact of employing the NRA theoretically by considering the autocorrelation
function of the array layout. We then develop a Costas-array-based silicon OPA
and experimentally demonstrate 2D beam steering with ~19,000 resolvable points
using only 127 phase shifters. This corresponds to the largest number of
resolvable points achieved by an OPA without sweeping the wavelength to the
best of our knowledge.
