Fiber-Optic Micro-Cavity Sensors With Enhanced Sensitivity By Vernier Effect

Fiber-optic micro-cavity sensor with enhanced sensitivity by Vernier effect not only inherits the advantages of fiber-optic interferometric sensor,such as anti-electromagnetic interference,corrosion resistance and remote measurement in extreme environment,but also makes up its deficiency of sensitivity.Currently,fiber-optic micro-cavity sensors with enhanced sensitivity by Vernier effect have become a research hotspot in the field of fiber-optic sensing,and widely applied in characteristic parameter measurement,such as temperature,refractive index,gas pressure and so on.However,there are still some limitations and technical problems to be solved in the application of high sensitivity and special environment.This thesis focuses on the fiber-optic micro-cavity sensors with enhanced sensitivity by Vernier effect,aims to solve the technical difficulties of the fiber-optic micro-cavity sensors with enhanced sensitivity by Vernier effect.Based on the theory of optical Vernier effect and the characteristics of fiber-optic interferometer,the schemes for integrating,sensitizing and eliminating temperature crosstalk of fiber-optic interferometric sensors have been proposed.Various fiber-optic micro-cavity sensors with enhanced sensitivity by Vernier effect have been designed and fabricated,and the sensing principle and sensing characteristics of the proposed sensors have been researched.In order to solve the temperature cross-sensitivity problem of the fiber-optic micro-cavity sensor with enhanced sensitivity by Vernier effect,the scheme of eliminating temperature crosstalk and realizing high-sensitive measurement by controlling the parameters of parallel fiber-optic interferometers and combining sensitive materials has been proposed.The fiber-optic gas pressure sensor with parallel dual-cavities based on Vernier effect has been designed and fabricated,which improves gas pressure sensing performance through the ultraviolet（UV）glue film,and eliminates temperature crosstalk through controlling the cavity length of sensing FPI and the thickness of UV glue film.The gas pressure sensitivity of the proposed sensor can reach-38.3 nm/MPa in the gas pressure range of 0.1 MPa to 0.7 MPa,and the proposed sensor is insensitive to temperature in the temperature range of 20℃ to90℃.On this basis,the fiber-optic temperature and gas pressure sensor with parallel polymer compound-cavities based on Vernier effect has been designed and fabricated,which realizes the high-sensitive measurement of temperature and gas pressure by using the different sensing characteristics of two fiber-optic FPIs and combining sensitive materials.Combining with the characteristics of polydimethylsiloxane（PDMS）glue,UV glue and optical Vernier effect,the proposed sensor exhibits a temperature sensitivity of 10.29 nm/℃ and a gas pressure sensitivity of-36.93nm/MPa.In order to improve the sensitivity of the fiber-optic micro-cavity sensor with enhanced sensitivity by Vernier effect,the secondary sensitization of traditional Vernier effect has been realized by using dual Vernier effect.The fiber-optic gas pressure sensor with parallel air-UV glue cavities based on dual Vernier effect has been designed and fabricated,which realizes the dual Vernier effect through the opposite gas pressure response of two fiber-optic FPIs.The gas pressure sensitivity of the proposed sensor can reach 131.88 nm/MPa through using the characteristics of UV glue and dual Vernier effect.The fiber-optic temperature sensor with parallel PDMS-filled cavities based on dual Vernier effect has been designed and fabricated,which realizes the dual Vernier effect through using the characteristics of two fiber-optic FPIs with opposite temperature response.Combining with the characteristics of PDMS glue and dual Vernier effect,the temperature sensitivity of the proposed sensor can reach 7.61 nm/℃.For the application requirements of high integration and sensitivity fiber-optic sensors,the scheme for integrating and sensitizing of fiber-optic interferometric sensor through combining the structural characteristics of hole-assisted fiber and optical Vernier effect has been proposed.The integrated fiber-optic gas refractive index sensor with cascaded air-silica cavities based on Vernier effect has been designed and fabricated,which realizes the gas refractive index sensing through using the air hole in the cladding of hole-assisted one-core fiber（HAOCF）as the transmission channel of the measured gas.Combining with the characteristics of HAOCF and optical Vernier effect,the gas refractive index sensitivity of the proposed sensor can reach-9462.4 nm/RIU,and the gas refractive index-temperature cross-sensitivity is only 8.7×10^-6 RIU/℃.The integrated fiber-optic temperature sensor with hybrid fiber-optic interferometers based on Vernier effect has been designed and fabricated,which realizes the structure of hybrid fiber-optic interferometers through combining the structural characteristics of hole-assisted suspended-core fiber（HASCF）and filling PDMS glue.The temperature sensitivity of the proposed sensor can reach-19.22 nm/℃ through using the characteristics of HASCF,the characteristics of PDMS glue,and optical Vernier effect.