Near-Visible Low-Power Tuning of Nematic-Liquid Crystal Integrated Silicon Nitride Ring Resonator

The development of compact, low-power, and high-performance integrated photonic phase shifters is critical for advancing emerging technologies such as light detection and ranging (LiDAR), optical information processing, and quantum applications. Liquid crystal (LC)-based phase shifters offer a promising solution thanks to their large refractive index contrast and low power consumption. However, it remains challenging to incorporate LCs into integrated photonics, and the operating wavelength has been limited to the near-infrared. Here, we demonstrate a liquid-crystal-based phase shifter operating at 780 nm, a relevant wavelength for cold-atom-based quantum applications, by incorporating nematic LCs (E7) into a silicon nitride (SiN) ring resonator. Our device achieves ∼2π phase modulation with a very low power of 2.1 nW and a low driving voltage of ∼7 V with an exceptionally low Vπ·L (half wave voltage·length) value of 0.014 V·cm, enabling precise control over light propagation in a compact footprint. This work marks a significant step toward realizing low-power, compact, and efficient LC-integrated photonic circuits based on the SiN platform for next-generation LiDAR and quantum optical systems.