Photonic chip packaging for extreme environments

Integrated photonic sensors have advanced significantly in the past decade for an ever-increasing range of applications, driven by the inherent scalability of integrated photonics combined with the precision of nanofabrication. Robust and ruggedized photonic fiber-to-chip bonding solutions are needed to develop photonic sensors that can operate in extreme environments. Here, we demonstrate a robust and high-efficiency method for photonic packaging that can operate in extreme environments ranging from cryogenic temperatures and high vacuum to high-dose radiation environments. Our packaging solution is also readily adaptable to high-temperature applications. In contrast to traditional polymer-based photonics packaging, we utilize direct chemical bonding of a V-groove optical fiber array to a photonic chip via hydroxide catalysis bonding to ensure operation across a wide range of extreme operating environments. The packaged chip is characterized from 360 K down to 3.8 K, demonstrating successful operation at cryogenic temperatures with 1 dB bandwidth of 50 nm per grating coupler in the telecom wavelength range, withstanding a cryogenic thermal shock of rapid submerging from ambient room temperature into a liquid nitrogen bath at 77 K. High-dose ionizing radiation testing is achieved by exposing the packaged chip to an electron beam corresponding to a cumulative radiation dose of 1.1 MGy. After irradiation, we do not observe degradation in insertion loss across the measured wavelength range from 1510 nm to 1630 nm. We bond several test dies and confirm the high-temperature compatibility of our bonding approach by measuring mechanical bond strength after annealing at 973 K. The annealed chips withstand 1 N/ mm 2 axial stress. Finally, we conduct a preliminary outgassing study to demonstrate high vacuum compatibility. Our packaging methodology can be readily adapted to different photonics applications, ranging from cryogenic circuits to extreme-environment in situ sensors.