Beamforming with Photonic Integrated Circuits for Millimeter Wave Communications and Phased Arrays

In this paper, two categories of 1 × 4 TTD-OBFNs are implemented within a 4 × 32 mm
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ultralow loss silicon nitride chip - switched delay line (SDL) based OBFN and optical ring resonators (ORRs) based OBFN. The SDL-OBFN is based on switches routing light among multiple physical paths. An improved ripple-free architecture is employed and 6 delay distributions with delay difference in range of 0-22.5 ps are achieved. The ORR-OBFNs employ three cascaded optical ring resonators as the tunable delay line for each channel with continuously tuned TTDs. For one delay channel, a dynamic tuning ranges of 209 ps for TTD bandwidths of 6.3 GHz are achieved, which corresponds to a phase shift of 37.57π for a 90-GHz signal. A 55° beam angle equivalent OBFN response for a 90 GHz half-wavelength pitch antenna array is achieved. Using the SDL-OBFN, the mmW beamforming experiment demonstrates 6 beamsteering angles in the range of -51° ~ 32°, and beam radiation patterns agree well with the simulations. To our best knowledge, this is the first TTD based beamforming experiment with Photonic Integrated Circuits for mmW signal.