Enhancing Beamforming Performance of Microcomb-Based Optical True-Time Delay Systems

The true-time delay (TTD) system for phased array antennas (PAAs) addresses the beam-squint problem effectively. Harnessing broadband microcombs as light sources in optical TTD systems provides numerous channels essential for beam pattern control. To increase channel density within widely used optical bands like the C-band, low repetition rate microcombs are indispensable. Moreover, judicious selection from these channels enables detailed reconfiguration of beam properties including beamwidth, sidelobe level, and null position. As PAA application scenarios grow more flexible and complex, the task of reconfiguring beam patterns to meet diverse requirements becomes increasingly challenging. Here, we demonstrate a TTD-based beamforming system with two reconfigurable arrays, utilizing a 25 GHz low repetition rate microcomb to achieve a beam scanning range from 0 $^{\circ }$ to 60.7 $^{\circ }$ . With a high channel density, we establish a 90-channel uniform array, facilitating superior high-order sidelobe suppression suitable for far-field spatial beamforming scenarios. We further refine our approach by selecting 12 channels from the 90-channel array to construct a Golomb-ruler array, thereby minimizing mutual coupling and achieving narrower beamwidth and higher resolution for precise close-range beamforming. Additionally, longer optical fibers are deployed to attain the desired steering angle owing to the lower repetition rate, and we assess the impact of the Kerr effect on both arrays. The results indicate that the Golomb-ruler array better mitigates Kerr effect impacts. Our study underscores the potential of microcombs in providing flexibly selectable channels for reconfigurable beamforming applications.