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Progress toward instantaneous microwave photonic spatial-spectral localization

With emergent fifth-generation (5G) communications systems harnessing ever-higher carrier frequencies and wider instantaneous bandwidths to enable denser user-space and higher data throughput, the ability to address high numbers of users becomes paramount. Existing digital beam-forming technology does not break down gracefully in the presence of a large number of data channels, and high-speed digital-to-analog converters (DACs) are both expensive and power-hungry. The RF-Photonic approach to millimeter-wave (mmW) imaging offers alleviations to this problem by relying on a low-speed phase-locked loop to mitigate phase variations incurred through mechanical means. We present a photonic mmW imager with a fiber arrayed waveguide grating (FAWG), enabling quasi-instantaneous spatial-spectral localization of all incident signals in the array field of regard through optical processing of the up-converted RF field. This configuration additionally enables recovery of the data encoded upon the received carriers through the use of a tunable optical local oscillator, with high-fidelity detection of quadrature amplitude modulation (QAM) signals demonstrated up to a 16-point constellations, and the recovery of multiple signals at once over a wide spectral separation. Additional techniques are presented, using multiple fiber projections to remove the ambiguity between spatial and spectral locations of multiple sources in an RF scene, providing quasi-instantaneous detection of the spatial-spectral location in frequency- and angle-space for each source incident upon the array. In a complete implementation, we expect such a system to possess the capability of simultaneous signal identification and data recovery, contained in a portable form factor for rapid deployment.