Liquid crystal-based phase modulators on low-loss silicon nitride photonic integrated circuit platforms

This work reports a unified liquid-crystal–integrated silicon nitride (LC–SiN) phase-tuning platform that operates efficiently at both near-visible (780 nm) and telecom (1550 nm) wavelengths, enabling low-loss, low-power, and highly efficient phase control for integrated photonics. At 780 nm, lithographically defined LC-filled trenches above SiN microring resonators with lateral electrodes provide strong overlap between the guided mode and a high-birefringence nematic LC, yielding continuous and reversible resonance tuning approaching one full free spectral range, corresponding to approximately 2π phase modulation with a record-low Vπ·L of 0.014 V·cm and static power consumption on the order of nanowatts. Time-resolved measurements reveal millisecond-scale electrically driven switching and multi-second relaxation dynamics, enabling quasi-static retention of the programmed optical state without continuous power, which is attractive for dense, reconfigurable circuits where configuration updates are infrequent. Extending this architecture to a multi-level SiN photonic platform at 1550 nm, the same LC–SiN integration scheme supports compact, voltage-controlled phase shifters and variable-tap amplitude modulators suitable for long delay lines, star couplers, and tunable couplers in complex dispersive circuits such as serial arrayed waveguide gratings. The combination of ultra-low-loss SiN waveguides and LC-based phase tuning addresses key limitations of conventional thermo-optic and carrier-based devices by simultaneously improving phase efficiency, reducing static power, and maintaining compatibility with both near-visible and telecom bands. Together, these results establish LC–SiN integration as a versatile, wavelength-agnostic platform for energy-efficient phase control in advanced photonic systems, including reconfigurable filters, programmable photonic signal processors, chip-scale LiDAR, and quantum and sensing architectures