Sensing And Application Base On S Tapered Fiber Sensor

S-tapered fiber is a new kind of tapered fiber that has appeared in recent years and it is essentially a very compact fiber Mach-Zehnder interferometer.S-tapered fiber is very sensitive to external refractive index and axial stress.To realize the measurement of other parameters such as humidity,magnetic field,temperat ure and other variables,we usually coat or package S-tapered fiber with some special materials.The size of a S-tapered fiber is only about 1 mm.and its structure is stable.It is very simple to prepare a S-tapered fiber with low cost.S-tapered fiber is widely used in various field and has a very good application prospect.However,the research about S-tapered fiber is mainly focused on the measurement of physical and chemical parameters of external environment,progress in application on biosensor is rather slowly and an ordinary S-tapered fiber can only measure a single parameter at the same time.In this paper,we make discussion about the theoretical analysis,preparation process,sensing characteristics and biosensor of S-tapered fiber.We build the mathematical model of the straight-tapered fiber under a local cylindrical coordinates according to the structure of the straight tapered fiber.The distribution of electromagnetic field in the straight-tapered fiber is analyzed and the Rsoft software was used to simulate the light propagation in the tapered fiber.We find that straight tapered fiber can realize the coupling between core mode and cladding mode,but its ability to excite higher-order modes is weak.On this basis,we consider that S-tapered fiber is formed by a bending of straight-tapered fiber.Mode coupling in S-tapered fiber has been analyzed and Simulation of light propagation in S-tapered fiber is done with Rsoft software.Finally,we find that it is much easier for S-tapered fiber to excite higher-order modes than straight-tapered fiber.A customized industrial fusion taper machine is used to prepare S-tapered fiber and we prepare S-tapered fiber with different structural parameters by setting the taper parameters different.It was found that the axial offset was the main parameter affecting the spectrum of S-tapered fiber and it should be set between 120 ?m and 160 ?m.The waist diameter of S-tapered fiber decays exponentially with the stretched length.Temperature and refractive index sensing experiment are performed by using a S-tapered fiber prepared in the laboratory.In order to realize the simultaneous measurement of refractive index and temperature,we make the S-tapered fiber with a FBG.Its refractive index and temperature sensitivity are 656.2 nm/RIU and 0.106 nm/?.The S-tapered fiber is used for the detection of human immunoglobulin G(Ig G)as it can excite the cladding modes.The process of preparing S-tapered fiber biosensor is introduced in detail and a micro-flow solution circulating fiber sensing system is designed to realize the detection of Ig G,its sensitivity is 0.6038 nm/(?g/m L).