Sensors Design And Application Research Based On Optical Microfiber Coupler

Optical microfiber coupler is a kind of passive optical fiber device made by fusing and stretching multiple optical fibers,which can realize the functions of optical coupling and beam splitting.Optical microfiber coupler not only has the advantages of low transmission loss,small size and strong anti-electromagnetic interference ability,but also has the remarkable characteristics of high nonlinearity and strong evanescent field of micronano fiber.Its transmission spectrum is very sensitive to the changes of coupler parameters and environmental parameters,so it becomes an ideal fiber sensor.In recent years,more and more research has been carried out on the sensing characteristics of optical microfiber couplers,and the related application is getting wider,which gradually extends to spectroscopy,nonlinear optics,biomedicine and other fields.Optical microfiber coupler has the unique advantages of ultra-high environmental refractive index sensitivity,multi-ports and thus makes it easy to integrate with other fiber device.The above advantages make it have high research value in high sensitivity,multi-parameter and multi-channel sensing.Based on the optical transmission and coupling theory of optical micro fiber coupler,this paper focused on the important issues such as high sensitivity temperature sensing,temperature and refractive index dual-parameter sensing and strain sensing with high sensitivity and large dynamic range.Sensing schemes based on different configurations of optical microfiber coupler are proposed,and the corresponding sensing characteristics are studied through theoretical analysis and experimental verification.Isopropanol has a high thermo-optic coefficient.Immersing the coupling region of optical microfiber coupler in isopropanol can effectively transform the environmental temperature change into refractive index change,thus transforming the ultrahigh sensitivity of optical microfiber coupler to refractive index into temperature sensitivity.Temperature sensing experiments were carried out in the temperature range of 30?-40?,and the obtained highest temperature sensing sensitivity is-6.20nm/?,which is at least one order of magnitude higher than the existing temperature sensing scheme of optical microfiber coupler.A dual-parameter temperature and refractive index sensor based on optical microfiber coupler is proposed,and its sensing characteristics are studied.A section of polarization maintaining fiber with high birefringence is used to connect two ports on the same side of optical microfiber coupler to form an optical fiber loop mirror based on optical microfiber coupler.Temperature and refractive index are sensed by polarization maintaining fiber and optical microfiber coupler,respectively.The temperature and refractive index response characteristics of the sensor were investigated experimentally.The temperature sensitivity of up to-1.33 d B/? was obtained by polarization maintaining fiber sensing area,and the refractive index sensitivity of up to 12020nm/RIU was obtained by optical microfiber coupler.A composite strain sensor based on optical microfiber coupler is proposed,and its strain sensing characteristics are studied.Optical microfiber coupler,Mach-Zehnder interferometer and Sagnac loop are cascaded based on the multi-port advantage of optical microfiber coupler.Optical microfiber coupler is used as strain sensing channel with high sensitivity and small dynamic range,while Mach-Zehnder interferometer is used as strain sensing channel with large dynamic range.The maximum strain sensitivity obtained by optical microfiber coupler is-9.70pm/??,and the strain sensitivity obtained by MachZehnder interferometer is-0.89pm/??.The strain sensor can meet the measurement requirements of high sensitivity,small range and low sensitivity,large range respectively.This work makes full use of the optical characteristics of optical microfiber coupler,constructs and implements a variety of new optical fiber sensors based on optical microfiber coupler,which provides an effective scheme for high-sensitivity temperature sensing,temperature and refractive index dual-parameter sensing and dual-channel strain sensing.The research work in this thesis improves the performance of optical fiber sensors based on optical micro fiber coupler,thus having a wider application space.