Highly sensitive hydrogen sensors using palladium coated fiber optics with exposed cores and evanescent field interactions

A novel fiber optic hydrogen sensor which is constructed by depositing palladium over an exposed core region of a multimode fiber is reported. The sensing mechanism is based on evanescent field interaction with the palladium coating. Since the length, thickness, and composition of the palladium patch can be controlled independently of each other, it is possible to increase the speed of our sensor at lower temperatures while maintaining its sensitivity. In micromirror sensors such an optimization is not possible due to a restriction imposed on their active area of interaction by the fiber optic cross-section. Micromirror fiber optic sensors, studied in the past, take advantage of the reflection/absorption of a palladium film deposited at the end of a fiber resulting in one sensor per fiber optic strand. On the other hand, many evanescent field-based sensors can be deposited over a single fiber optic strand. Using a 100 Å thick palladium with 1.5 cm interaction length, we could detect hydrogen in the 0.2–0.6% range with corresponding response times of 30–20 s at room temperature. At −10°C, these response times increased by a factor of only 2.