Investigation On Optical Fiber Twist Sensing Based On Polarization Characteristic

Owing to the characters of high sensitivity, compact and the application in the tough environment, fiber sensors have been widely applied in sensor field. This paper demonstrates the fiber twist sensors based on the polarization character of the fiber. The theoretical principles, sensor fabrications and applications of sensors are discussed in this work. The main contents are shown as follows:1. The development of the polarization character of the fiber was introduced. And the applications of polarization character in the field of the fiber twist sensing were simply presented.2. In this work, the polarization character of polarization-maintaining optical fiber(PMF) and tilted fiber Bragg grating(TFBG) was clearly studied. Because of the tilted plane of the TFBG, the circular symmetry of the fiber is destroyed, which results into the polarization of the cladding modes. Because of the refractive index difference between the orthogonal axis, the PMF can keep the polarization with no varies. When the fiber twists, the polarized direction of the input light will change between different polarized directions.3. A twist sensor based on tilted fiber Bragg grating of polarization properties was presented. This sensor was fabricated with a 1cm long TFBG characterized by an internal tilt angle equal to 10o. In the experiment, the transmission intensity on the strong loss wavelength cladding modes showed a quasi-sinθ changing with the twist angle varying for S- polarized or P-polarized input light. A sensitivity of 0.299 d B/o is achieved with the angle ranging from-180o to180o. On this basis, the twist sensor based on the polarization properties of the gold-coated TFBG was demonstrated. The sensitivity of 0.2957 d B/o was obtained with the angle ranging from-180o to180o.4. A twist sensor based on the Mach-Zehnder interferometer(MZI) with PMF was presented. By using the core-offset fusion splicing method, the MZI was constructed with PMF between two single mode fibers. The interferometer fringes of the fast axis or the slow axis will periodic change with the fiber twisting.