Study On Special Optical Fiber Dual Parameter Sensor Based On Surface Plasmon Resonance

Surface Plasmon Resonance(SPR)fiber optic sensors have many advantages,such as high sensitivity,light weight,and small size,which show certain application potential in the sensing field.In actual operation,the complex environment makes it difficult for a singleparameter refractive index sensor to avoid the influence of temperature on it,and a dualparameter sensor capable of simultaneously detecting refractive index and temperature has been paid attention to.In order to improve the performance of dual-parameter optical fiber sensor,this paper studies the optical fiber dual-parameter sensor based on surface plasmon resonance from both theoretical and experimental aspects.The details are as follows:Firstly,a double D-type microstructured fiber(MOF)for measuring refractive index and temperature is theoretically designed and studied.Gold was chosen to excite surface plasmon resonance.This fiber has two D-polished planes.A gold layer and a gold/polydimethylsiloxane(PDMS)layer were deposited on the two polished planes,respectively.Due to the structure of the two heterofilms of the fiber,two loss peaks appear in the loss spectrum.Simultaneous detection of refraction index and temperature is achieved.Seawater was chosen as the analyte,and the sensitivity of the refractive index reaches 1371 and1228 nm/RIU,respectively,and the sensitivity of temperature reaches-0.3 and-1.06 nm/℃,respectively.Finally,we obtain matrix expressions that can characterize both the refractive index and temperature of seawater.Secondly,in order to improve the sensitivity of the sensor and the detection range of the measured parameters.The refractive index and temperature sensing characteristics of the D-type double-core microstructured fiber coated with gold film were theoretically designed and studied.A gold film was coated on the surface and inside the cladding air holes of the D-type double-core microstructured fiber.The air holes of the gold film were filled with ethanol as a temperature-sensitive material.There are two cores in the fiber are Core I and Core II.The light passing through Core I is used to detect the refractive index of the analyte,and the light passing through Core II is used to measure the temperature.By optimizing the sensor structure parameters,its refractive index and temperature sensitivity were increased by 4500 nm/RIU and 0.3 nm/℃,respectively.Thirdly,a special optical fiber sensor based on surface plasmon resonance is experimentally studied,which can be used to measure the performance of refractive index and temperature at the same time.The sensor is composed of multimode fiber(MMF)-no-core fiber(NCF)-multimode fiber.The outer surface of the no-core fiber was coated with a silver film to excite surface plasmon resonance.Coating PDMS on the outer half of the silver film causes two dips in the transmission spectrum.The sensitivity of dip I to refractive index and temperature was 2121.43 nm/RIU and-0.32 nm/℃,respectively,dip II has not change with the change of refractive index,and the temperature sensitivity was-2.21 nm/℃.Finally,We get matrices for index of refraction and temperature.