| Distributed optical fiber sensing technology integrates sensing and transmission,which can obtain multi-dimensional information along the optical fiber varying with time.The technology has the advantages of large capacity,high sensitivity,miniaturization,and can be used in a variety of special environments to achieve long-term and stable measurement,which paves a promising way in the field of precision manufacturing,medical health,environmental monitoring etc.In recent years,with the development of technology and society,it is necessary to improve the sening spatial resolution to centimeter or even millimeter for more precise multi-dimensional sensing information.The traditional distributed optical fiber sensing technologies mostly adopt common optical fiber as the sensing carrier.In order to improve the spatial resolution,lots of researches have been studied in the light source,optical detection and signal processing method,which have obtained great achievement,but also result in the complexity and cost of the system.The utilization of novel sensing fiber is another effective way to improve the spatial resolution.This method is more flexible for different applications,which can improve the spatial resolution as well as take into account the sensing capacity and sensing distance.This paper focuses on the high spatial resolution distributed optical fiber sensing technology,and carries out innovative research from the sensing fiber and signal analysis technology.Three kinds of longitudinal microstructured fiber were studied for ultra-high resolution,large capacity and long distance sensing application as well as the distributed sensing mechanism and the sensing system.The main contents and chapters are as follows:(1)For the requirement of high spatial resolution sensing,the theories and modification technology based on longitudinal microstructured fiber had been studied.The sensing mechanism and interrogation technologies of longitudinal microstructured fiber had been researched through the theories of fiber Bragg grating and scattering enhancement points.Aiming at the requirements of longitudinal microstructured fiber fabrication process,the core modules such as fiber release device,fiber collection device,and stress control device were designed to develop a multi-functional fiber microstructure continuous fabrication platform,which can realize continuous fabrication along the fiber axis and flexible control in space for uniform and non-uniform fiber grating,microcavity structure and local scattering enhancement points etc.The movement speed of the optical fiber can be precisely controlled with the range of 6 mm/min ? 10000 mm/min,and the fabrication accuracy of microstructure is 5 ?m.This platform can realize automatic manufacturing amd support the fabrication of ultra-long microstructured fiber up to 50 km.(2)According to the requirement of ultra-high spatial resolution distributed sensing in short-range,the continuous microstructured fiber grating were proposed and researched as well as its sensing technology.The continuous microstructured fiber grating was designed by layer peeling algorithm and group delay control method to separate the wavelength channels,and a 21-channel grating was fabricated by the seamless ultra-violet writing technology.The temperature characteristics of the grating were studied,and the demodulation method based on waveform tracking was proposed for temperature sensing.The uniform temperature field,gradient temperature field and radiation temperature field were studied experimentally,achieving a 3mm spatial resolution and 63 mm range real-time temperature field monitoring with the maximum temperature gradient of 7.85?/mm.(3)In order to meet the requriment of large capacity with high spatial resolution,a distributed optical fiber sensing technology was proposed based on weak reflection FP microstructured fiber.The weak reflection FP microstructure with wavelength and frequency encoding capacity was designed as well as its multiplexing scheme,achieving the multiplexing capacity of 243 in a single fiber under the condition of 10 mm spatial resolution.The detection range was up to 2430 mm,which was an order of magnitude higher than the one-dimensional wavelength coding technology.Further,for the requirement of high sensitivity pressure detection in gastrointestinal motility monitoring,the soft polymer package method was utilized to enhance the sensitivity of lateral pressure.The theoretical model was established and the finite element method was used to analyze the key parameters of package such as elastic modulus,Poisson's ratio and diameter.The pressure sensitivity of the sensing fiber was enhanced 700 times than the bare fiber.A sensing demodulation system based on tunable FP filter and spectrum Fourier transform method was developed for the static and dynamic pressure response experiments,achieving 120cm/min dynamic pressure wave detection with a 10 mm spatial resolution,2.2 MPa/nm pressure sensitivity,0.46 k Pa pressure resolution,and0?40 k Pa pressure sensing range.(4)In order to meet the requirement of ultra-long sensing distance with high spatial resolution,the scattering enhanced microstructured fiber was proposed as well as its distributed sensing technology.The local defects were introduced in single-mode fiber core to build up equidistant scattering enhancement points with increasing strength along the fiber,and the sensing distance can reach 90.5km by segmented regulation method.A 17 km backscattering enhanced microstructed fiber was fabricated through single-pulse laser exposure,which enhanced the backscattering signal around 5d B.A high-resolution distributed liquid level sensing technology based on scattering enhanced microstructured fiber was proposed for the demands of large dynamic range and high-precision liquid level monitoring in the fields of petroleum transportation and storage,wastewater treatment,etc.A large-scale liquid level monitoring technology was proposed based on the temperature mutation effect of the gas phase and the liquid phase on the gas-liquid contact surface,and the sensitivity and spatial resolution of the liquid level measurement were further improved through the winding package.Combined with coherent phase demodulation technology,the dynamic liquid level measurement was realized with the spatial resolution of 74?m experimentally.Based on the17 km microstructured fiber,the liquid level measurement range could reach up to 85 m. |
PDF Full Text Request