Research On Sensors Based On Eccentric Core And Linear Array Multi-core Fiber

With the progress of science and technology and the rapid development of the Internet of Things,the demand for information acquisition is developing in a multidisciplinary way from production and processing to logistics convergence,from subtle control to the global Internet of things,from medical detection to national security.Fiber optic sensors have been widely used in engineering because of their advantages such as high sensitivity,fast response speed,excellent stability and adaptability to harsh environment.Traditional optical fiber sensors can no longer meet the requirements such as low crosstalk,high integration and multifunctionality,therefore the new type of optical fiber sensor is a key problem to be solved urgently.The work carried out in this dissertation is to design a variety of optical fiber sensors with different functions by use of the diversity of modes and structures in special optical fibers and comprehensively investigate the sensing characteristics based on theory and experiment.The properties of the sensor integrated inside the fiber have been explored.This work is of great significance to promote the development of optical fiber sensing technology.The main work of this dissertation includes:1.A Mach-Zehnder interferometer in the eccentric core few mode fiber has been propose using the core mode-core modes interaction.The LP₀₁ and LP₁₁ modes in the fiber core are simultaneously excited by the fiber fusion technology with displacement,and the cladding mode excitation is reduced by the fiber etched technology,thus the mode interference between the LP₀₁ and LP₁₁ modes in the fiber core has been realized.Compared with the core cladding mode interferometer constructed by the same fiber,the core mode-core mode dual-mode interferometer has higher refractive index sensitivity and lower temperature sensitivity.When the refractive index is 1.335?1.400,the average refractive index sensitivity of the interferometer is 1300.4 nm/RIU,and reaches the maximum value of up to 2565.2 nm/RIU when the environmental refractive index is about 1.400.At 20°C?200°C,the temperature sensitivity is only-9.6 pm/°C.The core-core mode Mach-Zehnder interferometer can be used as a high sensitivity refractive index sensor with low temperature crosstalk.2.A Mach-Zehnder interferometer has been designed based on few mode hole assisted eccentric fiber.The mode excitation characteristics of the fiber have been simulated and analyzed when the air hole is filled with and without liquid.The displacement distance of Mach-Zehnder interferometer has been determined when the optimal coupling occurs during the fiber splicing.The refractive index and temperature sensing characteristics have been simulated and verified by experiments.Because of the existence of the air hole,the hole assisted eccentric fiber few mode interferometer can be used as micro-channel refractive index sensor with low temperature crosstalk.A long period fiber grating with bending compensation has been proposed in hole assisted eccentric fiber.By means of optical fiber fusion technology with displacement,the core of hole assisted eccentric fiber is fused in the opposite radial direction and the long period grating is written symmetrically on both sides of the fusion junction.Since the gratings on both sides of the fusion junction have completely opposite bending responses during the radial bending,the fiber has an anti-bending effect.The bending sensitivity is only0.47 nm/m^-1.At the temperature of 30°C?210°C,the sensitivity of the structure to temperature is about 55 pm/°C.The Mach-Zehnder interferometer refractive index sensor based on the few mode hole assisted eccentric fiber can be used as an anti-bending temperature sensor.3.A Mach-Zehnder interferometer has been proposed in linear array 5-core fiber.The modal interference of the super-mode has been studied in a linear array 5-core fiber.The interference between the core mode and core mode is insensitive to the changes of axial strain and curvature,while the interference between the core mode and cladding mode is very sensitive to strain and bending perpendicular to the core alignment direction.The strain and bending sensitivities are-0.8 pm/??and 10.37 nm/m^-1,respectively.The proposed Mach-Zehnder interferometer can realize the sensing responses of different physical parameters by using different mode interferences.4.A fiber Bragg grating(FBG)has been proposed in heterogeneous double period linear array 6-core fiber.The super-mode characteristics of heterogeneous double period linear array6-core fiber have been discussed.Two independent super-mode groups are formed in two core groups with different sizes.In addition,fiber Bragg gratings have been written upon the six cores,respectively.The temperature sensitivity of fiber Bragg grating within each core is approximate 10 pm/°C and the axial strain sensitivity is approximate 1 pm/??.The proposed Bragg grating in heterogeneous double period linear array 6-core fiber can be integrated in the same plane,working at different resonant wavelengths,and it has potential applications in the fields of spatial division multiplexing,lasers and sensors.