Silicon-Integrated 8-Channel 6-bit Tunable Optical True-Time Delay Lines with High Switching Speed and Low Loss

Fast reconfiguration time of several nanoseconds is highly required for microwave photonic beamformers such as in 5/6G wireless communication systems. However, most previously reported integrated optical true-time delay lines (OTTDLs) have a response time of tens of microseconds. In this study, we propose and demonstrate silicon-integrated 8-channel 6-bit tunable OTTDLs with fast tuning speed for the first time. All the delay lines are identical with a delay step of 4.93 ps, and a maximum delay of 310.84 ps. With the overall optimized low-loss delay waveguides, 3-dB couplers, and electro-optic optical switches, we realize an OTTDL with an average fiber-to-fiber insertion loss of 11 (7) dB working in the electro-optic (thermo-optic) mode within a wavelength range of 1520-1580 nm. The electro-optic switching speed is 8 ns and 15 ns for the rising and falling time, respectively. By turning on PIN-diode-based variable optical attenuators (VOAs) to suppress leakages, the delay ripple can be suppressed to < 0.45 ps over a broad bandwidth of 20-43.5 GHz.