Research On Optical Fiber Twist Sensor Based On Polarization-maintaining Sagnac Ring Structure

Based on the difference of the orthogonal polarization modes in polarizationmaintaining fiber(PMF),a novel PMF Sagnac-loop interferometer(PSLI)is fabricated.PSLI has been paid much attention in the field of optical fiber sensing due to its merits of high stability,high signal-to-noise ratio,and ease of fabrication.In this thesis,the globaland local-torsion response characteristics of PSLI have been studied respectively,and a two-order Lyot-Sagnac filter based on angle-spliced PSLI is developed,which completes the simultaneous measurement of torsion and temperature with high discrimination.The main contents are as follows:(1)The transmission spectra of PSLI are analyzed by using the Jones matrix method.The wavelength and intensity responses of interference spectra are verified by the comprehensive global-torsion experiments.The response characteristics of local-torsion is deeply studied by varying twisting length and PMF length.The results show that the torsion sensitivity is negative proportional to the PMF length,and the wavelength sensitivity can be effectively improved by reducing the PMF length.When the PMF length is 7 cm,The torsion sensitivity as high as 852.1 pm/° is obtained in experiments.(2)The sensitive features of bias-twisted PSLI is studied based on the theory of twoorder Lyot-Sagnac filter.Then the wavelength responses of bias-twisted PSLI are theoretically and experimentally studied,and the linearity improvement and tunability of transmission spectra are strongly verified.The results show that,under bias-twisted PSLI,high linear response ?0.99 in the range from-360° ?360°is realized,with the sensitivity of 70.8 pm/°.Furthermore,the torsion responses at splicing point and single-mode fiber are studied.The experimental results show that in the range from-40°?40°,the linear responses of torsion in terms of wavelength and intensity are obtained,and simultaneous measurement of temperature and torsion is also completed.(3)A novel two-order Lyot-Sagnac is established by flexible and variable angleconnecting two segments of PMF with tiny difference of length.And the Vernier effect of interference spectrum is easily obtained and tuned.Then,a temperature sensing test is performed and the 14-time sensitivity improvement(22 nm/°C)is gotten.Moreover,the comprehensive experiments of torsion are performed.The results show that,when the splicing angle is equal to 45°,the fabricated two-order Lyot-Sagnac presents the most significant intensity modulation,and the sensitivity reaches 0.271 dB/° in the range from 135° to 175°,which can effectively eliminate the temperature crosstalk in a typical Sagnac interferometer.