Research On Performance And Optimization Of Excessively Tilted Fiber Grating Vibration Sensor

In many fields such as building structural health monitoring,aerospace,perimeter security,petroleum exploration industry,and so on,it is of great significance to accurately obtain information such as strain and vibration signals in real time.Fiber Bragg Grating Sensors have attracted much attention in the above sensing applications due to their superior strain sensitivity response,compact structure,corrosion resistance,and electromagnetic interference resistance.However,the traditional fiber Bragg grating?FBG?and long period fiber grating?LPFG?have limited the improvement of their sensitivity and the application of vector detection due to their inherent sensor limitations and cross-sensitivity of wavelength demodulation.In the research of this paper,On the basis of our research group's research on vibration sensing of cantilever beams with excessively tilted fiber grating?ExTFG?strength,we proposed the vibration sensing method of ExTFG with its optimized performance,including the vibration sensor performance research of ExTFG with fine diameter and cladding corrosion type ExTFG.Further research on the sensor bending vector characteristics and vector vibration sensing performance is made.Specific research contents include:1.Introduce ExTFG basic structure and derive its mode coupling theory,and analyze ExTFG core/cladding mode effective refractive index and other spectral characteristics in detail,and then study ExTFG SRI,strain,bending and vibration sensing characteristics.2.Research two kinds of ExTFG vibration sensors based on"performance optimization methods".First,an ExTFG vibration sensor writed in a special optical fiber is designed and manufactured.A small-diameter fiber grating structure design is used to achieve high-sensitivity vibration sensing.Experimental results show that the sensor's axial strain sensitivity can reach 4.68 pm/??.For bending strain,the sensor's bending strain sensitivity based on wavelength changes can reach 8.82 nm/m^-11 and based on intensity changes can reach 6.71 dB/m^-1,and using the sensor's resonance peak 3dB point for vibration detection,the maximum acceleration sensitivity can reach 531.92 mV/g,and the output stability is good.Then a vibration sensor based on ExTFG cladding corrosion is designed.The HF solution is used to etch the cladding of ExTFG standard single-mode optical fiber to optimize the performance of ExTFG vibration sensor.The experimental results show that the maximum acceleration sensitivity of the resonant peak 3dB point of the cladding etched ExTFG vibration sensor can reach 159.35 mV/g in the frequency range of 40²00 Hz.3.Research the vector vibration sensor based on ExTFG,and proposed to use the characteristic of refractive index uneven modulation in ExTFG sensor to realize vector vibration detection,and experimentally verifies the vibration direction correlation detection of two different types of ExTFG sensors.First,an ExTFG vector vibration sensor based on standard single-mode fiber is designed,and the static vector bending strain and dynamic vector vibration sensing characteristics of the sensor are studied.The experimental results show that the sensitivity of the sensor to bending strain in different directions can reach4.981 nm/m^-11 and has a maximum orientation sensitivity of 34.6 pm/(m^-1·deg),and the acceleration sensitivity and orientation sensitivity of the vibration signal can reach 74.14mV/g and 9.1 mV/deg respectively by using the resonant peak 3dB point of the sensor.Then,an ExTFG vector vibration sensor based on a small-diameter fiber structure is designed.The experimental results show that the sensor's bending strain sensitivity can reach a maximum of 8.342 nm/m^-11 in a curvature range of 0⁰.575 m^-1,and it has 22.8pm/(m^-1·deg)maximum orientation sensitivity,acceleration sensitivity and orientation sensitivity to vibration signals can reach 503.55 mV/g and 2.01 mV/deg,respectively.