Low-loss and Thermorefractive-stable Tantalum Pentoxide Integrated Photonics

Photonic integrated external laser cavities have the potential to significantly enhance laser frequency stabilization and narrow linewidth applications. One of the foremost challenges in the field of photonic integration today is achieving low-loss waveguides while effectively managing the thermo-optic response of the cavities. Tantalum pentoxide $\left(\mathrm{Ta}_{2} \mathrm{O}_{5}\right)$ stands out as a promising photonic material, thanks to its low thermo-optic coefficient (TOC) and minimal material loss. Incorporating $\mathrm{Ta}_{2} \mathrm{O}_{5} / \mathrm{SiO}_{2}$ waveguides into photonic circuits requires careful consideration of waveguide loss, device footprint, thermorefractive noise, optical input/output efficiency, and other critical functionalities. In this work, we present a Ta2O5 photonic platform designed to minimize propagation loss and thermorefractive noise. Using our CMOS-compatible fabrication technique, we demonstrate that these resonators possess intrinsic Q factors exceeding $10^{6}$, which corresponds to a propagation loss of $0.27 \mathrm{~dB} / \mathrm{cm}$ at 1550 nm. The temperature-dependent wavelength shift (TDWS) for the Ta2O5 resonators is merely $9 \mathrm{pm} / \mathrm{K}$. The thermorefractive frequency noise in the Ta2O5 microresonators is reduced by $\mathbf{5 0 \%}$ compared to $\mathrm{Si}_{3} \mathrm{~N}_{4}$ resonators.