Research Of Composite Film Special Fiber Temperature Sensor Based On SPR Effect

Special fibers are fibers with special properties and applications different from those of communication standard fibers.Its material doping,fabrication process,structural design,transmission wavelength,optical properties,mechanical and environmental properties all have particular characteristics.Therefore,in addition to being widely used as transmission medium of optical signal,special fiber also plays an unshakable important role in the sensing field.The no-core fiber and microstructure optical fiber involved in this study belong to the category of special fiber.The sensor that combines special fiber and surface plasmon resonance(SPR)technology has the advantages of wide detection range,high sensitivity,easy integration and support for real-time telemetry,which makes it show broad application prospects and potential research value.In this paper,an experimental study of temperature sensing by outer cladding of no-core fiber drawn in the laboratory based on optical waveguide and SPR principles.Based on the Finite Element Method(FEM),a composite film microstructure optical fiber temperature sensor is designed,and its temperature sensing characteristics are numerically analyzed.The main structure and research contents of this paper are as follows:Firstly,the transmission mechanism of light wave in fiber is given,and the theory of evanescent wave absorption and attenuated and total internal reflection in fiber is introduced.The generation of plasmons at the interface between metal and dielectric materials and the principle of SPR are analyzed.The simulation process and steps of the full vector FEM for microstructure optical fiber are mainly introduced,which lays the theoretical foundation for the research of special fiber temperature sensor based on SPR effect.Secondly,silver film was deposited on the outer surface of the no-core fiber made in the laboratory by silver mirror reaction,and then temperature sensitive materials ethanol and polydimethylsiloxane(PDMS)were wrapped on outside of the no-core fiber with silver film,respectively,for temperature sensing experiments.When light is transmitted from one end of the multimode fiber to the no-core fiber,evanescent wave formed interacts with silver film on the surface of the no-core fiber to produce SPR effect.The change of refractive index of temperature sensitive material with temperature will affect the movement of loss peak in transmission spectrum line.Further,the change of ambient temperature can be detected by the movement of sensor resonance spectrum line.The experimental results demonstrate that compared with ethanol,PDMS is more practical as a sensitizing material.When the temperature ranges from 30℃ to 100℃,the average temperature sensitivity is-2.0932 nm/℃(heating process)and-2.0729 nm/℃(cooling process),and the linearity is 0.9914 and 0.9809,respectively.Finally,in order to obtain higher sensitivity,a gold/PDMS composite film microstructure optical fiber temperature sensor based on SPR effect is designed.By analyzing the modulation effects of air hole size,hole spacing,temperature sensitive material thickness and gold film thickness on the amplitude of loss curve and corresponding wavelength,a temperature sensor with high sensitivity is obtained.Gold and PDMS are deposited on the outer surface of the microstructure optical fiber in turn,which improves the oxidation resistance and mechanical strength of the sensor.The simulation results show that when the temperature changes from-20℃ to 40℃,the average sensitivity of the sensor is 9.287 nm/℃,and the maximum sensitivity can reach 13.000 nm/℃.