Thermo-optic modulator with ultra-high extinction ratio for low-loss silicon nitride integrated photonics

Extremely low-loss silicon nitride integrated circuits is a potential platform for a growing number of frontier applications in quantum technologies, high-performance and analog computing, nonlinear optics, light detection and ranging (LiDAR), and biotechnologies. However, efficient optical modulation with a wide frequency response, high contrast, low power and scalable manufacturing remains one of the key challenges for silicon nitride integrated photonics. Here, we propose an integrated thermo-optic phase shifter with isolation trenches operating in the C-band. The fabricated thermo-optic modulator capable to achieve a $\pi$-phase shift shift at a power consumption of 65 mW, bandwidth of 12 kHz, and extinction ratio (ER) over 80 dB. Moreover, we systematically demonstrate its compatibility with low-loss silicon nitride photonic integrated circuits with microring resonators exibiting an average quality factor more than $5.9 \times 10^{6}$, which correspond to propagation loss of 0.058 dB/cm.