Application Of Fiber Bragg Grating Devices Based On Cobalt Doped Fiber

As one of the fastest-growing fiber-optic passive devices,since their appearance,optical fiber gratings have seen more and more applications with the continuous improvement of its fabrication technology,and have gradually developed into one of the most advanced and the most promising fiber-optic passive devices,having broad application prospects in many fields such as optical fiber communication and optical fiber sensing due to their own unique advantages.In this thesis,starting from the novel fiber grating sensing technology,the application of fiber grating devices in the field of optical fiber communication and optical fiber sensing is deeply studied.A narrow-band filter with all-optical adjustment and two novel hot-wire type microfluidic flow sensors are developed.This thesis first gives a brief overiew of the background and significance of the research,together with the development history.Then it discusses the application status and market prospects of fiber gratings and cobalt doped fiber in the field of communications and sensing,and summarizes the curren research hotspots of fiber grating sensing technology.Theoretical analysis of the fiber grating structure model and the basic theoretical analysis tools,including ray theory,coupled mode theory and transmission matrix method for non-uniform fiber grating are given.From the photosensitivity of optical fiber,the thesis discusses the commonly used photosensitivity model and photosensitivity enhance technology.Then,the several existing methods of manufacturing fiber Bragg gratings are briefly described,as well as the hydrogen-loading equipment and grating fabrication system used in this thesis.After that,a tunable narrow-band filter based on a fiber Fabry-Perot cavity structure inscribed in a cobalt-doped fiber is developed.The grating structure based on a cobalt-doped fiber is a new type of optical fiber device.The cobalt-doped fiber has an excellent photothermal conversion mechanism,so that all-optical tuning of the resonant wavelength of the grating can be realized.The Fabry-Perot cavity structure composing of a fiber Bragg grating pair can greatly improve the fineness of the resonance peak,realizing high-precision and high-resolution sensing,and after reasonably design the fiber Bragg grating length and Fabry-Perot cavity length,single longitudinal mode operation of the fiber filter can be realized.Furthermore,this dissertation also proposes a novel hot wire flow sensor technology based on a cobalt-doped fiber.An integrated microfluidic flowmeter based on fiber grating Fabry-Perot interferometer structure was designed by software simulation calculation.The flow rate sensing characteristics,including wavelength response,time response,sensitivity,and working ambient temperature of the manufactured flowmeter were verified through specific experiments and high sensitivity,high resolution,and high stability microfluidic flow sensing is achieved.The experiment results also proves that by increasing the power of the pump laser and reducing the size of the microfluidic channel,the flow rate detection sensitivity of the flowmeter can be further increased and the flow rate measurement range can also be enlarged.Finally,a micro-structured fiber Bragg grating based microfluidic chip is designed.The fiber Bragg grating inscribed in a cobalt-doped fiber was combined with the microfluidic chip technology.The software simulation is carried out first and then a special fiber grating numerical analysis method is used to calculate the flow sensor response of the sensor structure.This theoretically confirmed the feasibility of the microfluidics sensing solution.The designed sensing structure increases the contact area between the sensing unit and the microfluid,and greatly enhances the flow detection sensitivity.At the same time,using the unique flow rate calibration method of the specific microfluidic chip can effectively compensate for the ambient temperature changes,and expand the application of the microfluidic chip.