Optical fiber hydrogen sensor for concentrations below the lower explosive limit

We report a simple and inexpensive optical fiber hydrogen sensor which consists of a palladium-coated cladded multimode tapered fiber. The working mechanism of such a sensor is based on the absorption changes of the evanescent waves. With a conventional multimode fiber, a low-power LED operating at 850 nm, and a simple detection scheme we demonstrate some sensors. It was found that the sensor's performance can be adjusted with the taper diameter. The sensor is suitable for monitoring concentrations of hydrogen below 4% (the lower explosive limit) with fast response.