Millimeter-Wave and Sub-THz Phased-Array Imaging Systems Based on Electro-Optic Up-Conversion and Optical Beamforming

This article presents a class of phased-array systems that function as video-rate imagers in the millimeter-wave (mmW) and sub-THz bands. While the systems presented operate in the Ka-band (35 GHz) and W-band (77 and 86 GHz), the approach is scalable to the THz regime. Their operation is based on the upconversion of incident mmW and sub-THz signals to the optical domain using high-speed electro-optic modulators (EOMs) that are connected to each antenna element in a phased-array antenna. The output optical fiber from each EOM is relayed to a fiber bundle, or optical fiber array, from which the upconverted mmW/sub-THz signals are launched into free space. Because the upconversion preserves both the temporal and spatial coherence, through a spatial phase-control loop (SPCL), the launched sideband signals re-form the beamspace of the incident mmW or sub-THz signals, but in the optical domain. At this point, a lens performs a 2D spatial Fourier transform, to produce a real-time image of the mmW or sub-THz signals from the environment on a short-wave infrared (SWIR) camera, which renders the scene at video rates. The fundamental operating principles of these systems are presented, along with the historical progress in their development, and experimental demonstrations.