Modelling Study of a High Sensitivity Sagnac Temperature Sensor Based on Photonic Crystal Fiber

Optical fiber sensors are widely valued by scholars for their simplicity of manufacture, resistance to electromagnetic interference, chemical resistance and ease of distributed measurement. Interferometric fiber optic temperature sensors use the phase change of light to achieve sensing. Sagnac interferometer based temperature sensors are widely used in the sensing field due to their high sensitivity and ease of production. The change in the phase difference can lead to a shift in the interference spectrum, which can be analyzed as a function of temperature. It is an important research direction to design special fibers in Sagnac ring to improve the sensing performance of Sagnac-type temperature sensors. The flexible structural design and air-hole fill ability of photonic crystal fibers offer the possibility to achieve excellent properties of optical fibers. In order to improve the temperature range and sensitivity of Sagnac-type temperature sensors, a photonic crystal fiber design method with high birefringence and high temperature sensitivity properties is provided. The high birefringence of the fiber facilitates the demodulation of Saganc-type temperature sensors and the high temperature sensitivity of the fiber facilitates the sensing sensitivity of Sagnac-type temperature sensors. As the optical fiber itself has limited sensitivity to temperature, it can be made to have good temperature sensitivity by filling the air holes of the fiber with temperature sensitive liquid material. The electromagnetic field model of this photonic crystal fiber is developed in COMSOL and the fiber properties are analyzed and calculated. The effect of structure parameters on the birefringence and the temperature sensitivity of the fiber is analyzed using the finite element method, and the effect of the filling method and the type of filling liquid on the temperature sensitivity of the fiber is investigated on the basis of the determined structure. The optimal structure and filling method are determined. The results show that selective filling can achieve higher temperature sensitivity than full filling, and ethanol is the most suitable filling fluid compared to other temperature sensitive liquids. Under optimal conditions, the fiber achieves a temperature sensitivity of 2.050 7x10(-5)/degrees C and a birefringence of 5.96x10(-2) at 1 550 nm. The 2 mm length of this fiber is used in a Sagnac type temperature sensor to analyze the sensing characteristics by simulation, increasing in temperature from 0 degrees C to 75 degrees C in steps of 5 degrees C and using the trough of the transmission spectrum as a reference point to analyze the variation of the transmission spectrum with temperature. A polynomial fitting method is used to fit the wavelength and temperature in order to analyze the temperature sensitivity of the sensor, improve the accuracy of the fit and reduce the measurement error. The results show that the average sensitivity of the sensor can reach 11.28 nm/degrees C and the maximum sensitivity is 15.94 nm/degrees C in the range of 0 similar to 75 degrees C, with an average temperature measurement error of 0.126 9 degrees C. Compared to existing typical Sagnac temperature sensors, the Sagnac temperature sensor in this paper achieves a higher temperature sensitivity with a minimized fiber length, a larger temperature range and higher measurement accuracy. Therefore, the sensor has a promising application in the field of temperature measurement.