Power-referenced and self-calibrated PM-FBG vibroscope

A compact vibration sensing probe, in which a short section of polarization-maintained (PM) fiber stub containing a normal straight fiber Bragg grating (FBG) is spliced to another single-mode fiber without any lateral offset, is proposed and experimentally demonstrated. Two groups of well-defined resonances with ~ 7 nm wavelength separation have been achieved in reflection. Among them, the recoupled cladding modes at short wavelength side are extremely sensitive to fiber bending and provide the real-time vibration information by cost-effective power detection. Meanwhile, the unwanted power fluctuations and temperature perturbations can be referenced out by monitoring the core mode resonances at the longest wavelength.