A large-scale integrated optical phased array with digital beamforming

Abstract

Abstract Digital signal processing has driven much of the capacity growth in coherent fiber-optic communications, but its use in free-space coherent imagers and sensors has so far been limited. We report a 128-element optical phased array with a fully parallelized readout that performs beamforming in the digital domain at 1550 nm. The photonic integrated circuit consists of an array of waveguide grating antennas, each routed to its own balanced coherent receiver, with a common on-chip local oscillator delivered to all 128 receivers through a 1:128 binary splitter tree. Since every channel is digitized independently, we recover the per-channel amplitude and phase without on-chip phase shifters and perform image reconstruction by computing the array factor in software. Using 6 of the 128 elements, we obtain digitally reconstructed beams with an average half-power beamwidth of $$1.23^{\circ }$$ and a field-of-view of $$8.30^{\circ }$$ for illumination angles between $$-4^{\circ }$$ and $$+3^{\circ }$$ . Across the full array, the median common-mode rejection ratio is 57 dB and the median noise floor is $$-118.9$$ dBm in a 1 Hz bandwidth, corresponding to a per-channel sensitivity of $$-121$$ dBm/Hz. The phases extracted from the digitized channels show sub-degree noise, indicating that the coherent detection and digital processing chain is working as intended. The architecture removes the need for on-chip phase shifters and points toward a practical route to large-format, high-resolution coherent receiver arrays for free-space sensing, ranging, and optical communications.