Integrated multi-beam optical phased array based on a 4 × 4 Butler matrix.

We design and demonstrate the first, to the best of our knowledge, silicon-based multi-beam optical phased array (MOPA), incorporating a 4×4 Butler matrix beamforming network. The one-dimensional end-fire array consists of 16 emitters at a uniform pitch together with their corresponding phase shifters and is shared among the beams to realize large-scale aliasing-free beam-steering at reduced complexity. Experimental results show that the device is capable of individual beam aliasing-free operation with a field of view up to 46°. The steering envelope shows a plateau where the peak intensities fluctuate within 0.5 dB. The beamforming and beam-steering performance are also evaluated for simultaneous multi-beam operation. Our work validates the feasibility of beamforming-network-based MOPAs, which are promising for applications including light detection and ranging and free-space optical communication.