Research On Interference-type Dual-core Curvature Optical Fiber Sensing Technology

In recent years,optical fiber sensors have developed into a large-scale industry and have widely used in many fields,such as national defense security,industrial production,information transmission,daily life,and scientific research.The reason why fiber optic sensors are so widely used is that they can use the structural characteristics of optical fibers to measure a variety of physical quantities.Compared with other types of sensors,optical fiber sensors have many advantages such as high sensitivity,not susceptible to electromagnetic interference,chemical resistance,simple structure,easy to implement and can work in harsh conditions.Curvature is an important physical parameter for engineering construction,bridges and rails measure.The demanding of curvature measurement accuracy is increasingly in daily life.Usually,the curvature of the surface is calculated by the relationship between the strain and the curvature.This method of indirect curvature estimation is relatively low and inaccurate.How to improve the measurement accuracy and sensitivity of the curvature sensor has becoming a research hotspot.In this thesis,based on the theory of mode interference,using the structural characteristics of two-core fiber designed a two-core curvature fiber-optic sensor.The main research contents of the thesis are divided into the following parts:First,a brief introduction to the research background and classification of optical fiber sensors is given.The research status of several different types of optical fiber sensors is described in detail.The theory of optical fiber mode and mode interference are discussed.Secondly,We given the specific steps of finite element method?FEM?analysis.In addition,the mode field characteristics and optical waveguide transmission of the fiber are analyzed by this method.An interferometer with an eccentric structure was fabricated using a dual-core fiber.The influence of the structural parameters of the twin-core fiber on the power transmission of the twinaxes was analyzed.Two core power coupling effects were studied with effect of the fiber core distance,refractive index difference,radius difference,and fiber length of the twincore fiber.The change of the optical spot of the optical waveguide with the length of the coreless optical fiber was also analyzed.Different lengths of the coreless optical fiber were selected according to different core spacings.Third,based on the above theory,using the characteristics of different core structure parameters of the dual-core optical fiber,a dual-core curvature optical fiber sensor based on interference principle is proposed.The sensor consists of two single-mode fibers,two coreless fibers and a dual-core fiber.The finite element method is used to simulate and analyze the core spacing of 12?m and 16?m within the curvature range of 0.556m^-1to 0.833m^-1.The sensitivity of the sensor obtained at 22?m is-18.4 nm/m^-1,-21.68 nm/m^-1,and-34.73 nm/m^-1,respectively.The results show that the sensitivity of the sensor is proportional to the core pitch of the dual-core fiber.And the sensitivity of the curvature sensor when the length of optical fiber is taken as 2cm and 3.5cm is-17.1976nm/m^-11 and-18.4nm/m^-1,respectively,indicating that the curvature sensitivity of the sensor is affected by the length of the optical fiber.