Microfiber Sensing Technology Based On Brillouin Optical Correlation Domain Analysis

Fiber sensing technology has become a hot research topic because its sensing medium is fiber,compared with conventional sensing technology,which has many advantages such as anti-electromagnetic interference,corrosion resistance and easy to layout.With the development of fiber sensing,the main research direction of fiber sensing is to expand new sensing mechanisms and research new sensing fibers.As a new type of fiber that has been studied in recent years,microfiber is characterized by a very small fiber diameter,which enhances the evanescent field of light transmission in the fiber,and enhances the coupling of light to the external environment,thus obtaining a lot of new sensing features.However,because it is limited by the process level,it is generally short.And it is not easy to perform distributed measurements.In this paper,the high spatial resolution Brillouin Optical Correlation Domain Analysis(BOCDA)and microfiber are combined to explore the variation of Brillouin frequency shift of microfiber in different liquid environments.The details are as follows:(1)Based on the relationship between Brillouin frequency shift and effective refractive index,the relationship between the Brillouin frequency shift of the tapered fiber and the refractive index of the external environment is established,which lays a foundation for subsequent experiments.(2)In this paper,we build a high spatial resolution BOCDA system.We notice and analyze the bad point problem of high spatial resolution BOCDA system.Then we improve the traditional coding as a new type of cyclic code to increase the signal to noise ratio at the dead point more than twice.It realizes distributed measurement of Brillouin frequency shift of tapered fibers with a diameter of 2-9 μm,and the spatial resolution is 2.5 mm.(3)Liquid refractive index sensing experiments were carried out using 6-9 μm microfibers.When the external refractive index is between 1.34-1.44,the Brillouin Frequency Shift of fiber is linearly changed with the external refractive index,and the highest density of refractive index sensing is 377MHz/RIU,and the lowest sensitivity is 248MHz/RIU,which provides new means of measurement for the distributed refractive index sensing.