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

Here we propose and report a novel fiber optic hydrogen sensor which is constructed by depositing palladium over an exposed core region of a multimode fiber. 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. This is not possible in so called micromirror sensors due to a restriction imposed on their active area of interaction by the fiber optic cross- sectional area. 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 and it is only possible to have one sensor per a fiber optic strand. On the other hand, since many evanescent field-based sensors can be deposited over a single fiber optic strand, multiplexing can be easily accomplished using both time- domain and wavelength-domain methods. Using a 100 angstroms thick palladium with 1.5 cm interaction length, we could detect hydrogen in the 0.2% to 0.6% range with corresponding response times of 30 s to 20 s at room temperature. At -10 degree(s)C, these response times increased by a factor of only 2 which is impressive.