Ultra-Low-Loss Silicon Nitride Optical Beamforming Network for Wideband Wireless Applications

Three optical ring resonator (ORR)-based integrated ultra-low-loss silicon nitride 1 × 4 optical beamforming networks (OBFNs) for millimeter-wave (mmW) beamsteering are reported. The group delay ripple of multi-ORR delay line was theoretically optimized and quantitatively studied by applying a genetic algorithm. The optimized 3-ORR delay true time delay (TTD) responses were experimentally achieved with 208.7 ps and 172.4 ps of delay tuning range for bandwidth of 6.3 GHz and 8.7 GHz, corresponding to a phase shift of 17.1π and 14.1π for 41 GHz mmW signal. The TTD performance of the 3-ORR delay line was also verified by controlling the delay of 3 Gbps data stream. A 22° beamsteering angle equivalent OBFN delay distribution was achieved for 41 GHz half-wavelength dipole antenna array. Both the theoretical analysis and experiments exhibit that the topology with one ring shared could balance the system complexity and TTD bandwidth well. Using heterodyne up-conversion technology and a single delay path, 41 GHz mmW signal with 3 Gbps OOK NRZ data modulation was generated and delayed.