Manufacture And Application Research Of Spiral Core Long-period Fiber Grating Sensor

Optical fiber sensors have become the focus of research in recent years due to the advantages of high sensitivity,corrosion resistance,anti-electromagnetic interference,small size and light weight.Sensors made of fiber gratings that with different structures have been sequentially reported.For the current development trend of optical fiber sensors,in order to meet the needs of high sensitivity measurement,this paper will focus on the helical long-period fiber gratings(H-LPGs),and it will been systematically researched from four aspects that are theory simulation,production technology,sensor application and cross-sensitivity solution respectively.In this paper,the basic theory of long period fiber grating(LPG)is firstly studied.The effective refractive index of the core mode,the effective refractive index of the cladding mode,the relationship between the period and the wavelength are simulated by using two medium models.The coupling-mode theory is used to analyze the transmission spectrum.Then,a method of fabricating H-LPGs is proposed based on the three common LPG manufacturing methods.According to this method,a H-LPG manufacturing platform is set up and produce H-LPGs with stable performance successfully.After that,the fabricated samples are used to temperature and torsion sensing experiments,it is found that the resonant wavelength of H-LPG has a good linear relationship with the temperature and torsional parameters respectively.This phenomenon proves that H-LPG has potential application in the sensing field.Finally,in order to solve the troublesome problem of cross-sensitivity of temperature and torsion parameters,a H-LPG with opposite helix was designed and fabricated.Its transmission spectrum is a W-shaped spectrum with two loss peaks,and the two loss peaks drift in opposite directions under the action of torsion.Based on the H-LPGs with opposite helix,two solutions to the cross-sensitivity problem are proposed,they are double-wavelength method and double-intensity method.The research in this paper shows that the H-LPGs fabricated by the proposed method can achieve high-sensitivity measurement,and provides a meaningful reference for the research and development of optical fiber sensing.