Fabrication Of Fiber Bragg Grating And Two-parameter Sensing By Femtosecond Laser Phase Mask Method

In this paper,we focus on the phase mask method with femtosecond laser to write Fiber Bragg Grating(FBG)and femtosecond laser micromachining technology.Using this technology,a practical dual-parameter sensor for temperature and strain and a dualparameter sensor for temperature and pressure are produced.The main contents are as follows:1.The sensing application of fiber optic sensor and FBG are introduced.The research progress of femtosecond laser phase mask method for writing FBG at home and abroad is reviewed.The research background and significance of the temperaturestrain and temperature-pressure dual-parameter sensors are introduced.2.The writing mechanism of FBG written by phase mask method with femtosecond laser and the sensing mechanism of FBG on temperature and strain are studied,which lays a theoretical foundation for the following sensor design.3.The system for FBG inscription by the phase mask method with UV femtosecond laser and the fiber-loaded hydrogen sensitization system were prepared,and the system was used to prepare high quality FBG.The preparation process and spectral growth characteristics of FBG were studied.4.A temperature and strain dual-parameter fiber sensor based on hollow-core fiber and FBG cascaded is proposed.The experimental results show that the temperature sensitivity of the new fiber-optic sensor is 24.55 pm/°C and 12.76 pm/°C,respectively,and the axial tensile strain sensitivity is-0.70 pm/?? and 1.02 pm/??,respectively.By establishing the sensitivity matrix equation between temperature and strain,the crosssensitivity between temperature and strain can be effectively eliminated,and the simultaneous measurement of external temperature and strain parameters can be realized.5.A temperature and air pressure dual-parameter fiber sensor based on open-pore hollow-core fiber and FBG cascaded is proposed.The hollow-core fiber waveguide transmission conforms to the anti-resonance principle.After opening the pore by femtosecond laser micromachining technology,the external air pressure affects the refractive index of the air core,resulting in the drift of the resonance peak.Since the temperature change also causes the shift of the resonance peak of the hollow-core fiber,the cascaded FBG can effectively avoid the cross-response between temperature and air pressure,and achieve high-precision simultaneous measurement of temperature and air pressure.The experimental results show that the air pressure of the open-pore hollow-core fiber is as high as-3.847 nm/Mpa,and the FBG has no response to the air pressure.The temperature sensitivity of the open-pore hollow-core fiber and FBG is 24.6 pm/°C and 12.58 pm/°C,respectively.The measurement range of air pressure and temperature is 0.1~8 Mpa and 20~500 °C,respectively.The fiber sensor has a good application prospect in a high temperature and high pressure environment.