Miniature, All-Fiber Rotation Sensor Based on Temperature Compensated Wave Plate

This letter 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 lead-in PMF linearly polarized 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 0.03° was demonstrated, while the temperature sensitivity proved to be <;0.011 °/C. 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 temperature-induced errors in the presented setup.