Research On Temperature Sensor Based On Polarization-maintaining Fiber

Optical fiber temperature sensor has unique advantages such as small size,light weight,high sensitivity,and anti-electromagnetic interference.It has a wide range of applications in aerospace,marine environment detection,and biomedicine,which need to obtain temperature information.In this paper,the birefringence characteristics of polarization-maintaining fiber are simulated theoretically.On this basis,using the structural characteristics of Panda polarization-maintaining fiber,two kinds of temperature sensors based on Long Period Fiber Grating（LPFG）and Mach-Zehnder Interferometer（MZI）are prepared,respectively.By using a CO₂ laser to periodically etched the stress-applied part of the polarization-maintaining fiber,a polarizing-maintaining fiber long period fiber grating（PM-LPFG）temperature sensor with the ability to resist the interference of refractive index,strain,and bending is fabricated.In this paper,the formation principle of PM-LPFG is analyzed theoretically,and its temperature,refractive index,strain and bending sensitivity are measured experimentally.The temperature sensitivity of PM-LPFG is 83.1 pm/℃,while the refractive index sensitivity and strain sensitivity are-19.06 nm/RIU and 0.32 pm/με,respectively.The maximum bending sensitivity in the different directions is only 3.33 nm/m^-1.The experimental results show that the sensor is sensitive to temperature change but insensitive to refractive index,strain,and bending change.In addition,the length of the sensing structure is only 1 cm,so PM-LPFG has a good application prospect in the temperature monitoring of complex environments.A polarization-maintaining fiber interferometer（PMI）is proposed and experimentally verified for temperature measurement using the Vernier effect.The PMI is fabricated by inserting a section of polarization-maintaining fiber between two pieces of multimode fiber.Due to the birefringence of polarization-maintaining fiber,there are two orthogonal polarization modes with different transmission characteristics in polarization-maintaining fiber.The cladding mode interferes with two orthogonal polarization modes whose polarization directions are parallel to the slow axis and fast axis of the polarization-maintaining fiber,thus forming MZI-X and MZI-Y.By demodulation of the Vernier envelope generated by two orthogonal MZI,the temperature sensitivity of PMI reaches-757.27 pm/℃,which is close to the theoretically calculated temperature sensitivity（-657.44 pm/℃）.In addition,the length of sensor is only 15.4mm,which is much smaller than most Vernier effect-based fiber optic sensors.Therefore,PMI has great potential in temperature monitoring in a small space.In this paper,two kinds of temperature sensors with excellent performance and characteristics are designed based on polarization-maintaining fiber,which can be used in temperature measurement with different requirements and have good development prospects in practical applications.PM-LPFG has certain advantages in temperature sensitivity and measurement range and can avoid the interference of physical quantities such as refractive index,strain,and bending,it can be used in temperature measurement in complex environments.PMI uses two orthogonal MZI to form a Vernier envelope for temperature measurement,which improves the sensitivity and still have a relatively compact sensing structure.Therefore,it has potential application value in the field of temperature measurement.