Research On The Curvature Sensor And The Sensing Characteristics Based On The Hollow Core Fiber

As an important physical parameter,curvature can represent the structure and shape of the measured object,which is of great significance in civil engineering,aerospace,composite materials and other fields.Fiber optic sensor has many advantages in the field of curvature sensing,such as high sensitivity,anti-electromagnetic interference,and corrosion resistance.However,there are often some shortcomings such as high temperature cross-sensitivity temperature and low curvature range.Aiming at these problems,this thesis proposes the curvature sensor based on hollow core fiber(HCF),analyzes the two sensing principles of anti-resonant reflection guidance(ARRG)and Mach-Zehnder interference(MZI),and studied the sensing characteristics of the curvature sensor.The proposed sensor has the advantages of the large curvature measurement range,temperature-insensitive and torsion-insensitive.The major work of this thesis is as follows:1.The structural characteristics and light conduction mechanism of HCF are analyzed,and the sensing theories of ARRG and MZI are studied.The formulas of the resonant wavelength of ARRG and interference wavelength of MZI are theoretical derived.Numerical simulation software Rsoft is used to simulate the transmission of incident light in the structures of the HCF and the single mode fiber(SMF)-HCF-SMF.The effect of inner diameter and length of HCF on the transmission spectra of the above two structures is analyzed.2.A curvature sensor based on HCF is proposed,and its sensing theory,fabrication method and structural parameter is studied.A theoretical model of curvature sensing theory based on ARRG and MZI is established,and the temperature-insensitive of the sensor is verified.The manufacture method of the sensor based on HCF is studied.The influence of fusion parameter on transmission spectrums is experimentally analyzed.The influence of inner diameter and length of HCF on the ARRG-based resonant lossy dip and MZI-based lossy dip in transmission spectrum is experimentally analyzed.It provides a basis for the optimization of manufacturing method and design of structural parameters of the sensor.3.The sensor research system of curvature sensor based on HCF is designed and constructed.The curvature sensing experiment is investigated,the influence of temperature and torsion is studied.The curvature experimental results of the proposed sensor show that the curvature sensitivity is-0.54 nm/m^-1 and-2.02 nm/m^-1 in the curvature range of[0 m^-1,7.04 m^-1]and[7.04 m^-1,11.87 m^-1],respectively.And the experimental results show that the temperature sensitivity and torsion sensitivity is 5.54pm/? and-6.74 pm/(rad·m^-1),which verified that the sensor is temperature-insensitive and torsion-insensitive.