The Research On Refractive Index Sensing Based On The Optical Fiber Evanescent Field

The optical fiber sensing technology to measure the liquid refractive index has become a hot spot in fiber sensing applications in recent years. The fiber sensor probe of the refractive index can be designed for optical fiber grating, F-P cavity, multi-mode optical fiber and other micro-nano structure. It has small size, light weight, high sensitivy, anti-electromagnetic and some other characteristics. The optical fiber sensor shows attractive prospects in biological, medicine and food fields.In this paper, the PANDA type polarization maintaining fiber was studied as the researching object. Through the selective corrosion method, we prepare a polarization maintaining fiber structure without stress applying parts, and obtain the polarization dependent evanescent field.The use of orthogonal polarization mode interferometric techniques of polarization maintaining fiber has been studied for such stress applying parts missing fiber structure in refractive index sensing properties.The main work of this paper is carried out as follows:It analyzed the current typical optical fiber sensing technology used for measuring the liquid refractive index, and pointed out the significance and advantages of the optical fiber technology. The principle of the optical evanescent field for measuring the liquid refractive index was demonstrated theoretically. We analyzed transmission characteristics of the polarization maintaining fiber. Meanwhile we constructed a PANDA type polarization maintaining fiber with stress applying parts missing, and analyzed its evanescent field characteristics and test methods for key optical parameters.Combined with the etching process, we applied the different etching speed of the different materials to achieve selective etching for PANDA type polarization maintaining fiber. Experiment was conducted to study the preparation method of PANDA fiber without stress applying parts, as well as fiber birefringence changes during the stress applying parts missing. Based on orthogonal polarization mode interferential theory, we have studied the optical transmission characteristics with the changes of the external refractive index and temperature.The results show that the PANDA fiber without stress applying parts has obvious shape birefringence,which is a better performance refractive index sensing probe. The sensor has a high sensitivity, and the preparation process is simple and low cost. In the liquid refractive index sensing field,this structure has a high potential application.