Research On Material Thermo-optic Properties Based On Fiber-optic SPR Sensor

Since Otto and Kretschmann proposed the prism coupling structure to realize surface plasmon resonance?SPR?in the 1960s,SPR technology has attracted the attention and research of many scholars with its outstanding advantages and extremely broad application fields.After years of research and development by researchers,prism SPR sensors based on Kretschmann structure have been widely used in life science,clinical diagnosis,environmental monitoring and other fields.However,as the demand for applications continues to expand and increase,the drawbacks of prism SPR sensors are increasing.Therefore,compared with the prism structure,the optical fiber SPR sensor has become a research hotspot with its irreplaceable advantages.In this paper,the thermo-optical properties of fiber-optic SPR sensors are studied and theoretical simulations are carried out.A new method for measuring the thermo-optic coefficient?TOC?of materials is also proposed.The full text of the specific research work is as follows:1.According to the N-layer transfer matrix model,the refractive index sensing characteristics of the fiber SPR sensor were theoretically simulated using matlab software.2.Firstly,three kinds of fiber SPR sensors with mismatched core type,400?m core and 600?m core were fabricated and the refractive index sensitive characteristics were studied experimentally.Then,a fiber optic SPR temperature sensor was fabricated.The temperature sensing performance of the three fiber SPR sensors in the range of 25°C-200°C was studied by coating polydimethylsiloxane?PDMS?materials in the sensing region of the fiber SPR sensor.Experimental results of refractive index measurement and temperature measurement show that the refractive index sensitivity(S_RI)of the mismatched core structure SPR sensor and the temperature sensitivity?S_T?in the low temperature linear range are slightly higher than the other two.In addition,the experimental results show that the mismatched core structure has higher surface plasmon excitation efficiency than the other two.3.The mismatched core structure was chosen to study the effect of the length ofthe sensing region?L?on the temperature sensing performance of the fiber SPR sensor.A mismatched core structure SPR sensor of L=4mm,8mm,and 12mm was fabricated,and the repeated measurement was performed using the temperature measurement system built in the previous step.Finally,the L has almost no effect on the temperature sensitivity of the mismatched core structure SPR sensor,but it will affect the consistency of the sensor,and the consistency is better when L=4mm.4.A new method for measuring the thermo-optic coefficient of materials is proposed.A series of refractive index glycerol solutions were measured by using an L=4 mm mismatched core structure SPR sensor,giving a functional relationship n=f???_R?as a function of the refractive index n and the resonance peak shift??_R.The temperature sensing characteristics were measured by coating PDMS,absolute ethanol and saturated brine in the core mismatch structure sensing area of L=4 mm.According to the above functional relationship,the thermo-optic coefficients of the three materials were calculated as?dn/dT?_PDMS=-4.19×10-4RIU/°C,?dn/dT?_24%NaCl=-2.62×10-4RIU/°C,?dn/dT?_Ethanol=-5.99×10-4 RIU/°C.To the best of our knowledge,this is the first time that a thermo-optic coefficient has been detected by a fiber-optic SPR sensor.This miniaturized sensor will bring new life to the analysis of the thermal state and performance of materials based on its real-time and multi-channel detection capabilities,compactness and highly flexible implementation requirements.