Interferometric Fiber Optic Probe Sensor Sensing Characteristics For Pressure,Temperature And Vibration

With the implementation of Made in China 2025,China’s manufacturing industry,industrial production levels and production safety issues are also receiving more and more attention.A large number of sensors need to be installed in a wide range of industrial scenarios to monitor the operating environment in order to ensure the safety of production operations.However,in scenarios such as oil storage facilities and underground mines where combustion and explosion must be avoided at all times,traditional sensors can cause combustion or even explosion due to the ageing of the wiring.At this time,optical fiber sensors rely on their own advantages of light for signal transmission gradually in the field of sensors to reflect the value.In this paper,three kinds of sensors are made mainly using optical fibers as sensing units to explore their sensing performance.The main work of the paper is as follows.1.The development of fiber optic sensors after the introduction of the first optical fibers is briefly described,and the structure of several different interference types of fiber optic interferometers as well as their operating principles are illustrated.The current research status of Mach-Zehnder interferometer（MZI）,Sagnac interferometer（SI）and fiber grating is also briefly introduced.2.The current research status of fiber optic probe sensors based on Michelson interferometer（MI）and Fabry-Perot interferometer（FPI）at home and abroad is highlighted.The waveguide equations of optical fiber and the interference theory of light are also briefly described.The interferometric theory of Michelson interferometer and Fabry-Perot interferometer and their working principles are introduced in detail.3.An MI-based optical probe sensor using a single-mode fiber（SMF）spliced with a photonic crystal fiber（PCF）is made for pressure-oriented measurements.The structure of the PCF and the fusion splicing difficulties are briefly described.Mode simulations and theoretical calculations using the finite element method for the sensing structure determine that the interference is generated by the LP₀₁ and LP₁₁modes.Finally,the pressure response of the sensing structure is tested to obtain a sensitivity of 0.7 MPa/nm in the range of 0-0.9 MPa,with good repeatability,stability and response speed.4.Also based on MI made a fiber optic sensor for high temperature measurement,by using a fusion machine can be made on the fiber a waist cone area,after simulation to draw mode dispersion curve to determine the higher-order mode in the cone area is excited and core base mode interference.Considering that the reflectivity of the end face of the fiber is only 4%,in order to improve the quality of the signal of the sensing structure,the end face of the fiber was coated with a gold film,which increased the reflection strength by 16 d B.Next,the temperature response of the sensor was tested and the sensor was measured to operate in the range of room temperature to 900°C with a temperature sensitivity of 80 pm/°C（100°C to 450°C）and 109pm/°C（450°C to 900°C）,with good stability and repeatability in high temperature environments after annealing.5.The FPI-based interferometer was formed by splicing a capillary tube with a SMF and silicon dioxide microspheres（SDM）inside the capillary tube（CT）with UV adhesive to form a three-beam interferometer.Simulations of the sensing structure using the beam propagation method（BPM）were carried out to explain the working principle of the sensing structure,and simulations of the sensor spectrum were carried out to verify the three-beam interference principle.Finally,a test system was built to determine the response of the sensing structure to vibration and the vibration frequency response was measured in the range of 700 Hz to 35 KHz.The directionality of the sensor placement was tested and the amplitude ratio after fitting the input signal to the output signal was calculated to obtain a solid frequency of 5.8 KHz for the sensing structure.