Optical fiber tip acoustic resonator for hydrogen sensing.

A microscale acoustic resonator fabricated on a standard single-mode fiber tip was demonstrated as a hydrogen sensor. The fabrication of the resonator involved standard fiber cleaving and splicing, radio frequency sputtering, focused-ion-beam patterning and deposition, and wet etching. A submicrometer layer of platinum was coated on the vibration arms of the resonator serving as a catalytic heater upon hydrogen exposure. The heat locally raised the resonator temperature, which led to an acoustic resonance frequency shift. The sensor's resonance frequency at 1.7 MHz shifted 1170.4 Hz upon exposure to 1% hydrogen concentration; the sensitivity of the sensor was estimated to be better than 0.1%.