Research On Optical Fiber Temperature Sensing Characteristics Based On Interference Filter

With the wide application of temperature sensor in production automation,ocean exploration,aerospace industry and other fields,optical fiber temperature sensing technology has attracted extensive attention because of its strong anti-electromagnetic interference,high sensitivity and wide dynamic response range.In recent years,how to improve the temperature sensitivity and resolution of optical fiber temperature sensor has become a research hotspot.The sensing characteristics of the cascaded interferometers are different from the traditional optical fiber temperature sensing structure of single interferometer.In this paper,vernier effect and harmonic vernier effect are introduced into the traditional optical fiber temperature sensing structure to improve the temperature sensitivity,and the structure of parallel Sagnac interferometer(fiber Sagnacinterferometer,FSI)and Mach Zehnder interferometer(Mach-Zehnderinterferometer,MZI)and the structure sensing module of double Sagnac ring are designed and proposed.There are great innovation in the structure and principle.Firstly,the optical path of each sensor structure is analyzed in detail and simulated.Finally,the correctness of the theory is verified by experiments.The main research contents are as follows:The main contents are as follows:(1)The research background and significance of the subject are introduced,and then the classification and application of optical fiber temperature sensor are summarized.And the research status of cascade Vernier effect,parallel Vernier effect and harmonic Vernier effect of optical fiber temperature sensor in recent years,and the main contents of each chapter are summarized.(2)The basic principle and the free spectral range(Free Spectral Range,FSR)of Sagnac ring and MZI in the interferometric sensor are analyzed theoretically.The results of mathematical analysis show that the free spectral range of FSI will follow the polarization maintaining fiber(Polarization).The length of Maintaining Fiber,PMF)decreases with the increase of length,while the free spectral range of MZI decreases with the increase of the length difference between the two arms.Then the Vernier effect is introduced to improve the sensitivity of the optical fiber temperature sensor,and the cascade Vernier effect and parallel Vernier effect are theoretically deduced and simulated.Finally,under the expansion of Vernier effect,the harmonic Vernier effect is theoretically analyzed and simulated.(3)An optical fiber temperature sensing structure based on FSI and MZI in parallel is designed.Firstly,the optical path of the structure is analyzed theoretically,and then the simulation verification is carried out.Finally,it is proved by experiments that a single FSI only has the temperature sensitivity of 1.65nm/ ℃,while the structure with FSI and MZI in parallel can amplify the temperature sensitivity to 12.9nm/ ℃.The gain coefficient is 7.82,which is very close to the theoretical result 7.9.The correctness of the theory is verified.(4)A double Sagnac ring sensitized optical fiber temperature sensing structure based on harmonic Vernier effect is designed.firstly,the optical path of this structure is theoretically analyzed and simulated,and the temperature sensitivity of single FSI interferometer optical fiber sensing structure,double Sagnac ring optical fiber sensing structure with Vernier effect and double Sagnac optical fiber sensing structure with harmonic Vernier effect are compared.It is proved that the temperature sensitivity of the optical fiber temperature sensor with harmonic Vernier effect is up to 29.01nm/ ℃,which is 17.58 times higher than that of a single Sagnac interferometer and 1.74 times that of a double Sagnac ring with basic Vernier effect.