Vibration Sensor Based on the Resonance Power Leakage in a Tapered Capillary Fiber

A compact all-fibre vibration sensor based on power leakage at resonance wavelengths of a tapered capillary fiber is proposed and experimentally demonstrated. A section of the capillary fiber was selectively etched by using hydrofluoricacid, which formed a tapered region in the capillary fiber. Two Fabry-Perot resonators are formed in the same capillary fiber due to the differences in cladding between the tapered region and original cladding. The leaky mode of the guided light can be achieved at resonant wavelengths of two Fabry-Perot resonators, which results in lossy dips in the transmission spectrum of the capillary fiber. The tapered region in the capillary fiber is supposed to be slightly bent due to the vibration, which results in a change of the resonance condition for one Fabry-Perot resonator due to the photoelastic effect. The experimental results show that a signal-to-noise ratio of 60 dB is achieved, and the fibre vibration sensor has a wide frequency response from 5 to 10 kHz. The tapered capillary fibre possesses high sensitivity and low temperature cross sensitivity.