Multiplexable Low-Temperature Fiber Bragg Grating Hydrogen Sensors

A palladium-coated fiber Bragg grating (FBG) inscribed in high attenuation fiber (HAF) capable of measuring hydrogen concentration at -150 C, well below the 4% explosion limit, is presented. The low-temperature performance of the sensor was improved by heating the gratings as much as 300 K above the ambient temperature with highly attenuated infrared laser light. The sensitivity and response time of the FBG hydrogen sensor were studied as functions of fiber temperature. Through the selection of length and the loss per meter of the HAF, the self-heating scheme demonstrated here enables numerous FBG hydrogen sensors to be multiplexed in a single fiber for multipoint hydrogen sensing using a single fiber feedthrough.