Research On The Integrated Fiber Fabry-perot Interferometers And Its Sensing Application

The miniaturization,integration and high sensitivity of optical fiber sensor is one of the important development directions in the field of optical fiber sensing technology.With the improvement of fiber microstructure and special fiber preparation technology,fiber microstructure interferometer has made great progress.Compared with other optical fiber sensors,Fabry-Perot(F-P)can more effectively enhance the interaction between light and matter by introducing micro-cavity structure into the optical fiber or using integrated air cavity formed by natural flow channels in microstructure special optical fiber,thus attracting much attention.Based on this,this paper uses the unique advantages of multi-core fiber and large air hole microstructure fiber to design a variety of integrated fiber F-P interferometers.Through cutting,splicing,tapering and other processes,the preparation of F-P interferometers is carried out,and its sensing characteristics are measured and systematically analyzed.The main research work of this paper is as follows:(1)The research status of large air microstructure fiber,single fiber F-P interferometer and integrated fiber F-P interferometer are summarized.Based on the principle of light coherence,the theoretical model of F-P multi-beam interference of optical fiber is constructed,and several important parameters affecting the reflectance spectrum characteristics are simulated.The structure classification of F-P interferometer is introduced.The general theoretical formula is deduced for the sensor characteristic analysis.(2)A kind of parallel F-P interferometer with double-closed air cavity is designed and manufactured by using seven-core fiber and double-hole fiber and combining with special fiber fusion technology.According to the requirements of the sensors parallel integration,improve the welding technology,build the theory model and the bend sensor of measuring principle at the same time,stress,and bending direction,temperature sensing characteristics,such as the experimental measurement and analysis,the experimental results show that the parallel air-cavity F-P interferometer can eliminate cross-sensitivity of temperature,measurement of stress and bending with good repeatability and linear effect.(3)In order to solve the problem of low bending sensitivity of parallel F-P interferometer with double-closed air cavities,a cascade F-P interferometer is designed and manufactured by taking advantage of the sensitivity enhancement characteristic of optical cursor effect and combining with eccentric-core fiber and hollow-core fiber.The cause and influence factors of Vernier effect are analyzed and deduced systematically.By designing three combinations of different cavity lengths for experimental comparison and analysis,vector bending sensors with different sensitivity and amplification multiples are obtained,and the main sources of errors are analyzed.(4)Using the structural characteristics of the parallel integrated F-P interferometer that can be used for ‘point' measurement,combined with the melting tapering technology,a parallel F-P interferometer with a single closed air cavity was designed and manufactured for temperature compensation of high sensitivity liquid refractive index measurement.This is the use of its closed cavity and external isolation to achieve a single temperature measurement,open cavity introduced microstructure channel can be more effective to enhance the interaction between light and matter to achieve high sensitivity liquid refractive index measurement.In general,the thermal light coefficient of liquid is two orders of magnitude larger than that of air,so it is of practical significance to realize temperature compensation through integrated method.