Self-heated all-fiber sensing system for cryogenic environments

We present a new design of an all-fiber sensor system to enhance the low-temperature sensing performance of cryogenic fuel. Fiber Bragg gratings (FBGs) are inscribed in high attenuation fibers (HAFs), which absorb in-fiber light to raise the local sensor temperature in a cryogenic environment. The heated sensor displays improved sensitivity and response time to measure multiple parameters. Two sensing applications are described in this paper. First, a HAF-FBG sensor coated with palladium is used to detect hydrogen concentration well below the 4% explosion limit at 173 K. Second, an array of three aluminum-coated sensors is capable of measuring the liquid level at 77 K. In addition, through the selection of the length and attenuation coefficient of HAF, numerous FBG sensors can be multiplexed on a single fiber for multipoint sensing using a single fiber feedthrough.