Research On Photonic Crystal Fiber Temperature Sensor Based On Surface Plasmon Resonance

Photonic crystal fiber（PCF）has been widely used in optical devices due to its unique structure,which exhibits excellent performance such as high birefringence,infinite single mode transmission,tunable dispersion,and so on.Currently,various types of PCF temperature sensors have emerged.The application of SPR technology has opened up a new avenue for temperature sensing in PCFs.Its high resolution,real-time and fast characteristics perfectly match the compact and flexible design of PCF.SPR-PCF temperature sensors have become one of the important research directions in the sensing field.In this paper,two high sensitivity sensing models are designed,and finite element calculations are performed using Comsol Multiphysics software to deeply optimize and analyze the proposed structural parameters for the purpose of improving the sensing performance parameters.The main tasks are as follows.Firstly,a D-shaped high-sensitivity and high-figure of merit SPR-PCF temperature sensor is designed,which can reduce the complexity of air hole coating and liquid filling.A gold film is coated on the polished D-shaped photonic crystal fiber plane to enhance the effect of plasmon resonance.On the outside,a mixture of ethanol and chloroform with high thermal optical coefficient is used as a temperature sensitive material.The arrangement of air holes is only two layers,simplifying the structural design.The sensing characteristics of temperature sensors are analyzed by simulation and the optimal structural parameters are selected.The results show temperature detection range for this sensor is-5 to 60℃,with a maximum sensitivity of 6.36 nm/℃and an impressive figure of merit of 0.3440/℃.Compared with various PCFtemperature sensor,This SPR-PCF temperature sensor has a significant improvement in both sensitivity and FOM value,which can greatly enhance the detection efficiency and accuracy of the sensor.A new type of D-shaped SPR-PCF temperature sensor structure has been proposed to address the issues of narrow temperature detection range,high limiting loss,low birefringence and sensitivity.The introduction of elliptical air holes in the PCF cladding destroys the symmetrical structure of the optical fiber,resulting in higher birefringence.The flexible design of elliptical air holes allows for adjustable birefringence,which better distinguishes the direction of the mode field.The transmission characteristics of the sensor,such as mode loss and sensitivity,as well as the influence of sensing material and structural parameters on the sensing performance were analyzed by finite element method.The results show that when the temperature decreases from 60℃to-50℃,the resonance peak of the sensor moves towards the long-wavelength direction.At a temperature of-50℃,the core fundamental mode loss was found to be only 5.07d B/cm,with a maximum sensitivity of 10nm/℃and a resolution of 4.85×10^-3RIU.In addition,the index fitting of temperature and resonant wavelength is great.The temperature sensor has a high sensitivity response in the near-infrared region,and its low limitation loss characteristic can improve the transmission distance of the optical fiber.It can be widely used in geological exploration,water quality monitoring and other fields.