Optical fiber-tip Fabry–Perot interferometer for hydrogen sensing

A novel optical fiber-tip Fabry–Perot interferometer (FPI) coated with Pt/WO3 film was demonstrated as a hydrogen sensor. The air-cavity of FPI was formed by inserting a single mode fiber (SMF) into a partially polymer-filled glass capillary. A layer of Pt/WO3 was coated on the capillary of the FPI serving as a reaction heater upon hydrogen exposure. The heat locally raised the FPI temperature, which led to the length of air-cavity decrease due to the volume expansion of polymer. Thus, the dip wavelength of interference spectrum yielded a blue shift. The temperature compensation method based on an optical switch was proposed to eliminate the effect of ambient temperature fluctuation. Experimental investigations demonstrated a high sensitivity of −5.1 nm/% at a low hydrogen concentration ranging from 0% to 0.5%.