Highly Efficient Phase Change Material Assisted Reconfigurable Optical Delay Line Based on Cascaded Coupled-Resonator Optical Waveguides

Microwave-phased array antenna system plays a pivotal role in wireless communication in which a compact, power-efficient, fast, continuously tunable delay line with flexible broadband operation driving each antenna is a crucial component. This article reports the design of a novel reconfigurable true-time delay line (TTDL) in the low-loss Si3N4 TriPleX waveguide platform with two cascaded coupled-resonator optical waveguides (CROW), each consisting of only two racetrack ring resonators operating at resonance. Unlike conventional thermo-optic tuning, low-loss phase change material (PCM) GeSe is used to realize reconfigurable TTDL for the first time, offering several advantages. First, the localized tuning effect of GeSe and its strategic orchestration breaks the delay-bandwidth constraint in conventional ring resonators, enabling simultaneous and independent tuning of delay and bandwidth. Second, PCM stimulated through electrical pulses enables fast response (1.4 μs) and two orders of lower power consumption than the conventional thermo-optic tuning in Si3N4 platform, thanks to larger refractive index modulation. Utilizing multilevel operation of PCM, the delay tuning range is found to be 114.8 ps with a low loss-to-delay ratio of 0.03 dB/ps and a flat-top response having ripples <1 ps over a compact footprint of 2.52 mm2. Moreover, taking advantage of PCM's non-volatile nature, a compact optical beamforming network chip is designed through parallel arrangement of the proposed TTDL, enabling dynamic adjustment of bandwidth from 2 to 6.7 GHz with ripples <1 ps corresponding to a point of view of ±60°.