Tantalum Pentoxide Integrated Photonics: A Promising Platform for Low-Loss Planar Lightwave Circuits with Low Thermo-Optic Coefficients
Zhenyu Liu, Wen Yao, Mingjian You, Xiaolun Yu, Ning Ding, Weiren Cheng, Zhengqi Li, Xingyu Tang, Fei Guo, Dan Lu, Qiancheng Zhao
Abstract
Photonic integrated external laser cavities are transformative components in laser frequency stabilization and linewidth narrowing applications. A key challenge in contemporary photonic integration is to realize low-loss waveguides while balancing the thermo-optic response of the cavities. Tantalum pentoxide (Ta 2 O 5 ) has emerged as a promising photonic platform due to its low thermo-optic coefficient (TOC) and low material loss. Incorporating Ta 2 O 5 /SiO 2 waveguides into a photonic circuit requires trade-offs among waveguide loss, device footprints, thermorefractive noise, optical I/O efficiency, and other desired functionalities. In this work, we present a Ta 2 O 5 photonic platform that emphasizes low propagation loss and low thermo-optic sensitivity. We demonstrate that the intrinsic Q factors of these resonators exceed 10 6, corresponding to a propagation loss of 0.27 dB/cm at 1550 nm, using our CMOS-compatible fabrication technique. The temperature-dependent wavelength shift (TDWS) of the Ta 2 O 5 resonators is merely 9 pm/K. The thermorefractive frequency noise of the Ta 2 O 5 microresonators is predicted to be half smaller than that of Si 3 N 4 resonators. Several key building blocks of integrated external laser cavities were demonstrated, including high- Q resonators, self-coupled microresonators, Vernier ring resonators, Sagnac loop mirrors, edge couplers, and Y-branch splitters, which contribute to a comprehensive suite of planar lightwave components on the Ta 2 O 5 platform. A narrow-linewidth hybrid-integrated laser has been demonstrated, utilizing a distributed feedback (DFB) laser diode self-injection locked to a Ta 2 O 5 microresonator. A fundamental linewidth of 1.6 kHz has been obtained. The distinctive optical characteristics of the Ta 2 O 5 waveguides could have a broader impact on high-capacity, temperature-robust, and multifunctional photonic integrated circuits, which are essential for the next-generation photonic computing systems, quantum photonic circuits, and beyond.