Study On Thin-core Fiber Interferometer For Sensing Application

With the continuous development of China's economy and society,the progress of science and technology,researchers who launched a lot of research on the sensor that have an important impact on the industrial,environmental fields.Because of its small size,corrosion resistance and high stability,optical fiber sensor attracts more and more researchers' attention.Optical fiber sensor has good sensing characteristics for many traditional physical parameters,such as temperature,strain,bending and refractive index,and has good application in engineering field.In this paper,a novel fiber sensor based on optical fiber interferometer is introduced,and its sensing characteristics for different physical parameters are discussed in this paper.1.A thin-core fiber-based Mach-Zehnder interferometer(MZI)is proposed and a multi-parameter measurement sensor is developed.The two single-mode fibers are used to connect the thin-core fibers to form a MZI structure,and the external environment parameters are measured by the interference wavelength shift.The use of thin-core fiber doped with high concentration of germanium,so the core and cladding has a large refractive index difference.In ensuring a good free spectral range,the sensor size is greatly reduced.The temperature,refractive index,strain and bending were measured,and the high temperature sensitivity was obtained.2.This paper presents a microstructure M-Z dual parameter measuring sensor for writing Fiber Bragg grating(FBG)on high germanium doped fiber.The GeO2 content of high germanium doped fiber core is as high as 98%,and the refractive index difference between the core and cladding is great.The excellent photosensitive property makes FBG writing very easy.It can get the extremely short grating length and higher reflectivity,thus the size of the sensor is greatly reduced,in the field of fiber Bragg grating sensors have potential applications.The temperature,refractive index,strain and bending were measured simultaneously by the sensor.3.A microstructure PH measurement sensor based on germanium doped fiber is proposed.The tapered structure of the M-Z interferometer is formed by pulling the high germanium-doped fiber by using the fiber pulling cone technology.The PVA/PAA solution was prepared by making a mixture of polyvinyl alcohol(PVA)and polyacrylic acid(PAA),which was then coated onto the tapered structure via layer-by-layer technique.The PVA/PAA membrane structure in different pH values of the solution,the result of expansion effect will change the refractive index around the sensor,resulting in interference wavelength or intensity changes.By measuring the interference wavelength shift or optical intensity of the sensor,the measurement of PH value is realized.