Research On Microcavity Of F-P Sensing Characteristics Based On Graded-Index Few Mode Fiber

In recent years,optical fiber sensors have many advantages,such as small size,high sensitivity,anti-electromagnetic interference and so on.It attracted the attention of domesic and foreign research scholars.The fiber Fabry-Perot(F-P)fiber sensor not only has high detection sensitivity and resolution,but also compact structure and simple demodulation,and it have been widely used in the measurement of temperature,refractive index,tension,strain and other physical quantities.Based on the research background of F-P sensors with different structures prepared by different fabrication methods at home and abroad,two kinds of F-P sensors with different structures are prepared by the method of chemical etched,and their transmission characteristics and sensing characteristics are deeply studied.The main contents are included as follows.Firstly,the basic principles of several interferometric fiber sensors are introduced,the interference principle of light and the principle of multi-beam F-P interference are studied in detail.Moreover the transmission principle of double-beam interference,three-beam interference and four-beam interference when multiple reflectors is mainly discussed.Secondly,the F-P sensor of single-cavity structure based on the few mode fiber is proposed and prepared.The theoretical model of three-beam interference in the single-cavity structure is established,the transmission characteristics are simulated.The transmission spectrum and the sensing characteristics of temperature and refractive index of the sensor are studied in experiments.Thirdly,the temperature sensitivity enhancement experiment of F-P sensor based on single-cavity structure of few mode fiber is proposed and carried out.The theoretical model of temperature sensitivity enhancement experiment is introduced in detail and the simulation is carried out.The influence of structural parameters of different sensors on the temperature sensitivity enhancement effect is studied in experiments.Finally,the F-P sensor of double-cavity structure based on the few mode fiber is proposed and prepared.The theoretical model of four-beam interference and five-beam interference is established,their transmission characteristics are simulated.The temperature sensing characteristics of the four-beam interference and five-beam interference sensors are experimentally studied,and the strain sensing characteristics of the four-beam interference sensor are studied according to its unique structural characteristics.