This paper presents a miniature, all-fiber fiber optic twist/rotation sensor. The proposed sensor consists of polarization maintaining lead-in fiber (PMF), a short section of standard (fully circularly symmetric) single-mode fiber, which is exposed to twist/axial rotation, an all-fiber quarter-wave wave plate, and a reflective layer. This sensor exploits the inability of a short-section circular symmetric single-mode fiber to change the polarization state or spatial E-field vector orientation of an optical wave when exposed to mechanical twist/rotation. Thus, the twisting of a single-mode fiber in the proposed configuration causes displacement of the lead-in PMF and wave-plate axis. This enables encoding of the twist angle into a power ratio of the leadin PMF LP modes that is propagated in a backward direction by the application of a wave plate, which can be straightforwardly measured by a simple interrogation system. The proposed design allows for compact sensor design with sensors active lengths below 5 mm. The unambiguous angular measurement range of the proposed sensor is 45°. An angular resolution better than 0.0355° was demonstrated, while the temperature sensitivity proved to be less than 0.011 °/C. In order to achieve low temperature sensitivity of the sensing system, a combination of different PMFs was used to eliminate the temperature sensitivity of the PMF based wave plate, which is the main source of temperatureinduced errors in the presented setup.
Miniature, all-fiber rotation sensor based on temperature compensated wave plate
