Low-loss, fabrication-tolerant, and highly-tunable Sagnac loop reflectors and Fabry-P\'erot cavities on thin-film lithium niobate

TL;DR

This paper introduces low-loss, highly tunable Sagnac loop reflectors and Fabry-Pérot cavities on thin-film lithium niobate, enabling efficient, fabrication-tolerant photonic components for scalable integrated circuits.

Contribution

It presents a novel approach using self-calibrated Sagnac loop reflectors to build low-loss, high-Q cavities and demonstrates power-efficient thermo-optic phase shifters with thermal isolation.

Findings

Achieved intrinsic quality factor of 2 million for Fabry-Pérot cavities.

Reduced power consumption of thermo-optic phase shifters by over 10 times.

Demonstrated fabrication-tolerant, highly tunable photonic components.

Abstract

We present low-loss ($<1.5\%$) and power-efficient Mach-Zehnder interferometers (MZIs) on thin-film lithium niobate. To accurately measure low MZI losses, we develop a self-calibrated method using tunable Sagnac loop reflectors (SLRs) to build cavities. Fabry-P\'erot cavities constructed from these fabrication-tolerant SLRs achieve an intrinsic quality factor of $2 \times 10^6$. By implementing thermal isolation trenches, we also demonstrate a $>10\times$ reduction in power consumption for thermo-optic phase shifters, achieving a $\pi$-phase shift ($P_\pi$) with just 2.5 mW. These tunable and efficient components are key for scaling up to complex photonic integrated circuits.