Non-Contact Fiber Vibration Sensor Based on Intracavity Modulation of an Extrinsic Fabry–Perot Interferometer

This paper describes a phase-demodulated fiber-optic sensor suitable for non-contact vibration detection. The sensor is based on an extrinsic Fabry-Perot (F-P) cavity, formed by a capsulated sensor head and the probed surface. The sensor head, bonded on a piezoelectric (PZT) stack, is driven by a continuous sinusoidal wave, which introduces phase modulation in the interference signal. The varied small displacement induced by vibration of the surface under test is detected utilizing an improved phase-generated carrier technique. The configured F-P sensor is compact and highly sensitive, since neither extra optical path nor frequency modulation of light source is employed for demodulation. Characterization experiment is also conducted using a PZT vibration exciter. The sensor exhibits a high signal-to-noise ratio of 41 dB at 1 kHz and noise limited detectable phase level of 6.3 × 10
^-5
rad, corresponding to a minimum vibration sensitivity of 7.8 pm.