Athermal micro-ring resonators based on LN–TiO2 hybrid waveguides over a wide wavelength range

We propose and experimentally demonstrate a hybrid waveguide combining lithium niobate (LN) and titanium dioxide (TiO2) to mitigate temperature-induced wavelength shifts in ring resonators. By leveraging the negative thermo-optic coefficient of TiO2, we experimentally demonstrate a significant reduction in temperature-dependent wavelength shift (TDWS) in micro-ring resonators. Over the temperature range of 15°C to 75°C, the TDWS is reduced to −0.8 pm/°C, which is two orders of magnitude lower than the 18.6 pm/°C experimentally measured in the LN micro-ring without TiO2. We also demonstrated stable performance over a wide wavelength range from 1500 to 1600 nm, with temperature-induced wavelength shifts between −3 and 2 pm/°C. This represents the best performance for temperature drift compensation based on structural adjustments on the lithium-niobate-on-insulator platform. The fabricated ring resonator exhibits a high extinction ratio up to 15 dB and maintains low loss despite a slight decrease in the quality factor (Q-factor) attributed to the non-uniform TiO2 deposition, given that TiO2’s absorption spectrum is mainly concentrated in the ultraviolet and part of the visible light range. This design offers promising applications in temperature-stable, low-loss optical devices, with potential for optical communication.