Hydrogen Sensor Based on Palladium Coated Side-Polished Single-Mode Fiber

This paper reports a fiber-optic hydrogen sensor based on a side-polished single-mode fiber coated with a palladium (Pd) thin film whose optical characteristics change as it absorbs hydrogen. The optical transmission loss of the sensor depends on the hydrogen gas concentration through the complex electric permittivity of the Pd film. An optimal design for the sensor has been pursued to obtain both high sensitivity and short response time. When exposed to 4% hydrogen gas, the optimal change output power obtained in this experiment was 1.2 dB (32%) with a rise time of 100 s.