Preparation And Research Of Novel Fiber Grating Sensors With Low Cross Sensitivity

In the field of sensing,all-fiber grating plays an important role because of the light weight,corrosion resistance,electromagnetic interference resistance and other properties.Among them,the excellent sensing characteristics of long period fiber grating have made many scholars scramble to study.In this paper,the single-mode fiber and the special fiber are designed to be cut and spliced together to prepare a novel long period fiber grating.In addition to showing excellent sensing characteristics in temperature,bending and displacement,the designed sensors also have the advantage of small crosstalk between the two physical parameters,which is manifested as the high sensitivity temperature sensor with low strain,bending and refractive index interference,the high sensitivity bending sensor with low temperature crosstalk and the wide measurement range displacement sensor with low temperature crosstalk.The main work is summarized as follows:Firstly,in order to obtain a high sensitivity temperature sensor with low crosstalk,the ultra-long period fiber grating is fabricated by alternately splicing the fixed length of the graded index multimode fiber（700μm）and the single-mode fiber（1000μm）using the self-imaging property of the graded index multimode fiber.The sensor is only sensitive to temperature,but insensitive to refractive index,strain,bending.Secondly,the 50μm step index multimode fiber and single-mode fiber are arranged in a fixed period composite way to prepare the superstructure long period fiber grating.The bending sensitivity of the sensor is up to 17.28 d B/m^-1 by amplitude demodulation.In addition,the low temperature-bending cross sensitivity of 4.772×10^-4 m^-1/°C also improves the accuracy of bending measurement.Finally,a displacement sensor with large measuring range is proposed in this paper.A long period fiber grating is fabricated by alternately splicing multimode fiber and single-mode fiber.Then it passes through a hollow capillary tube and is bent into a balloon-shaped structure.By changing the bending diameter of the balloon-shaped structure,the transmission spectrum always has a monitored resonant peak in different wavelength ranges.The experimental results show that the monitoring range reaches 74 mm.The low temperature sensitivity of about 10pm/°C also reduces the influence on displacement measurement.The three novel LPFGs proposed in this paper not only exhibit excellent sensing characteristics,but also have low crosstalk ability,which can effectively suppress the interference of other parameters on the monitoring physical quantity and improve the measurement accuracy.