| Surface Plasmon Resonance(SPR)is an emerging sensing and detection technology that integrates physical optics,biochemistry and other disciplines in recent years.It has many advantages such as strong electromagnetic interference ability,simple and convenient operation,etc.,and has been widely used in biochemical sensing fields such as biological detection,chemical reaction monitoring,environmental monitoring,and disease diagnosis.The traditional SPR sensor is formed by depositing a layer of highly conductive metal film such as gold or silver on the surface of the prism.Compared with traditional space prism SPR sensors,fiberbased SPR sensors have many unique advantages,such as: small size,high integration,remote telemetry,easy networking,etc.The development trend of online telemetry has received extensive attention in recent years.Due to the geometrical characteristics of the optical fiber,the incident angle of the optical fiber SPR sensor cannot be changed like the space prism structure,and the SPR resonance wavelength can only be slightly changed by controlling the side throwing depth of the optical fiber and the parameters of the metal film,and the resonance wavelength can be changed in a large range.There are few methods,which makes it difficult to realize multi-channel measurement in series.In order to solve the problem that the resonance wavelength of traditional fiber SPR sensors is not easy to adjust in a large range,so as to realize distributed measurement of multiple sensing channels on the same fiber,this thesis proposes a SPR sensing scheme based on helical core fiber.The resonance wavelength,dynamic range and sensitivity of the SPR sensor can be adjusted by changing the pitch of HCF,so we can use the cascaded helical core fiber SPR sensor to achieve distributed measurement,and realize ultrahigh sensitivity temperature detection based on the spiral core fiber SPR sensor.In this thesis,the theoretical analysis and experimental research on the helical core fiber SPR sensing technology is carried out,and the key technical problems in the preparation process of the helical core fiber SPR sensor are overcome.The main work includes the following contents:1.Study on the mechanism of helical core fiber SPR sensor.This thesis proposes to theoretically derive the helical core fiber SPR sensor by using the whispering gallery mode and the mode expansion transmission method,and establish a two-dimensional equivalent curved waveguide model for theoretical simulation calculation.Considering the transmission loss of the light wave in the helical core fiber,the effects of the fiber parameters such as the refractive index of the fiber,the geometric size,the torsional period size,and the thickness of the remaining cladding on the optical transmission and SPR excitation were explored.The resonance wavelength of the SPR sensor and the torsional pitch,Relationship between fiber parameters such as remaining cladding thickness.2.Research on the preparation method of helical-core fiber and its SPR sensor.The research on the preparation method of the helical core fiber was carried out,and the helical core fiber was prepared by the method of thermal fusion and twisting.The influence of temperature field,gravity field and other factors on the formation of the helical core fiber was discussed.The system realizes the preparation of helical core optical fibers with different pitches and different periods,carried out research on the optical fiber side polishing technology,developed a set of optical fiber side polishing system,and used the wheel polishing method to grind and polish the twisted area of the optical fiber.Realize the removal of the fiber cladding to expose the fiber core;the mechanism of ion sputtering coating is studied,and the parameters such as vacuum degree,sputtering current,sputtering target distance and sputtering time during sputtering coating are discussed.In view of the influence of quality,a low-cost method for quantitative plating of nano-gold films using a small ion sputtering instrument was proposed,and the film thickness accuracy reached ±1 nm.3.Fabricate a single-period helical core fiber SPR sensor,and build a fiber SPR sensing experimental system.The effects of the helical core fiber pitch,the refractive index of the surrounding medium,and the side throw depth on the helical core fiber SPR sensor are theoretically and experimentally studied.The results show that the resonance wavelength and sensitivity of the helical-core fiber SPR sensor can be tuned by changing the pitch of the helicalcore fiber.The SPR sensor fabricated with 1.9 mm pitch helical core fiber has an average sensitivity of up to 7400 nm/RIU in the refractive index range of 1.375-1.385.4.Prepare two helical core fiber SPR sensors with different pitches on the same fiber to realize cascaded multi-channel sensing.The interaction between the SPR resonance spectra of the helical core fiber SPR sensors with different pitches is studied when they are cascaded.When the pitch difference between the two cascaded helical core fiber SPR sensors is greater than 2.0 mm,the SPR resonance spectra of the two sensing channels can be obtained.It is completely separated and does not affect each other,and the two resonance valleys can be clearly obtained;on the contrary,when the pitch difference between the two cascaded helical core fiber SPR sensors is small,the resonance spectra of the two SPR sensing channels are mixed together and cannot be distinguished.In addition,the refractive index sensitive characteristics of the cascaded helical core fiber SPR sensor are studied,and the results show that the sensing characteristics of the cascaded sensor are not affected,and multi-channel simultaneous measurement can be achieved.5.The helical core fiber SPR sensor is used for temperature sensing to achieve ultra-high sensitivity detection of temperature.Since the SPR sensor is very sensitive to the change of the external refractive index,the high thermo-optic coefficient material PDMS is coated on the outside of the helical core fiber SPR sensor to construct an ultra-high sensitivity temperature sensor.According to the characteristics of the helical core fiber SPR sensor,the smaller the pitch,the higher the sensitivity to the external refractive index,so the temperature sensitivity of the helical core fiber SPR temperature sensor can also be adjusted by changing the pitch.With a pitch of 2.5 mm,the temperature sensitivity can reach 19.6 nm/℃ at 20 ℃In summary,this thesis proposes a new type of helical core fiber SPR sensor,which can adjust the SPR resonance wavelength and sensitivity by changing the pitch of the helical core fiber,which solves the difficult problem of adjusting the fiber SPR resonance wavelength and sensitivity.The spiral core SPR sensor is connected in series to realize the cascaded spiral core fiber SPR sensing structure,which can realize distributed measurement and multi-parameter measurement;using the high sensitivity of the fiber SPR sensor to the refractive index change,the spiral core fiber SPR sensor is coated with a high thermo-optic coefficient The material PDMS constitutes a high-sensitivity temperature sensor.The helical core fiber SPR sensor has the advantages of small size,high integration,high precision,and easy realization of distributed sensing. |
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