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Unitary optical processors (UOPs) are task-specific computing units that can ultimately enable ultrafast and energy-efficient unitary matrix-vector multiplications based on the interference between coherent optical beams. The UOP using multiport directional couplers (MDCs) holds great promise in large-scale integration because of its unique robustness against fabrication errors. Here, we demonstrate a 10-port robust UOP on a silicon photonic chip, which is so far the largest-scale UOP using multiport directional couplers. We further show the unique flexibility of this architecture by demonstrating operations for both the transverse electric (TE) and the transverse magnetic (TM) polarizations, which has never been realized in previous UOPs. This flexible and robust architecture is suitable for various scenarios in deep learning, optical communication, and quantum information processing.

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Optical phased arrays (OPAs) are promising beam-steering devices for various applications such as light detection and ranging, optical projection, free-space optical communication, and optical switching. However, previously reported OPAs suffer from either an insufficient number of resolvable points, or complicated control requirements due to an extremely large number of phase shifters. To solve this issue, we introduce the non-redundant array (NRA) concept to the OPA devices. Based on this design, we can realize high-resolution OPAs whose number of resolvable points scales quadratically with the number of antennas N . In contrast, that of traditional OPAs scales only linearly 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. To the best of our knowledge, this corresponds to the largest number of resolvable points achieved by an OPA without sweeping the wavelength.

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