Polarization-maintaining fiber-optic-grating vector vibroscope

A fiber-optic vector vibroscope based on orthogonal polarization cladding-to-core recoupling is demonstrated. A compact structure in which a short section of polarization-maintained (PM) fiber stub containing a straight fiber Bragg grating (FBG) is spliced to another single-mode fiber. Two well-defined orthogonally polarized cladding modes reflected by the PM-FBG are recoupled at the junction and the coupling intensity shows an extremely high sensitivity to bending in the corresponding orthogonal directions. Both the orientation and amplitude of the vibrations can be determined unambiguously via dual-path power detection of these recoupled orthogonal-polarimetric cladding modes (LP1;12 and LP1;13). Since spectral information is not required, temperature changes do not affect the sensor response, and power fluctuations can be referenced out by monitoring the power in the core mode (LP0;1) resonance.