Research On Preparation And Sensing Properties Of High Regeneration Rate Regenerated Fiber Bragg Grating

Fiber Bragg Grating(FBG)is a widely used passive optical device in the fields of sensing and communication.However,conventional Type I FBG lose their transmission capability gradually and the periodic modulation of refractive index disappears when operating in environments above300 °C,which limits their application in industries such as energy,metallurgy,aerospace,etc.Currently,it is known that thermal annealing can regenerate Type I FBG,resulting in Regenerated Fiber Bragg Grating(RFBG)that effectively avoid thermal decay,thereby overcoming the limitations of FBG in high-temperature sensing applications.However,RFBG produced through thermal annealing often suffer from low regeneration rates and poor mechanical performance.This paper focuses on the limitations of RFBG,with high-temperature monitoring as the application background and the development of high-performance RFBG for high-temperature sensing as the research objective.The research revolves around FBG fabrication,RFBG production,packaging,and application,with the following main contributions:(1)Addressing the fabrication issues of seed FBG,an optical system based on a 248 nm excimer laser was constructed for phase mask method inscription of FBG.The spectral evolution during UV exposure of FBG,as well as the influence of grating length and applied pre-stress on the spectral characteristics,were studied to achieve the preparation and characterization of high-performance FBG.Multiple FBG with different center wavelengths were fabricated using a phase mask plate,solving the cost issue associated with the phase mask method.(2)To address the low regeneration rate of RFBG,the spectral evolution during the annealing process of seed FBG was investigated.The influence of insulation conditions on the regeneration rate of RFBG was compared and analyzed.By integrating quartz phase transition laws,stress relaxation theory,and X-ray diffraction results of RFBG,the impact of irregular crystallization induced by volume expansion during quartz phase transition on the regeneration rate of RFBG was analyzed and discussed.The results indicated that the phase transition temperatures of quartz were575 °C and 870 °C,and RFBG exhibited the highest regeneration rate under these conditions.By improving the original uniform heating annealing method,a non-uniform heating annealing method for RFBG was proposed,leading to the successful production of RFBG with a high regeneration rate of up to 81.8%.Further performance testing revealed that high-regeneration-rate RFBG also possessed higher mechanical performance,operational lifespan,and stability.(3)To address the issue of poor mechanical performance of RFBG,tube-shaped and spherical encapsulation structures of RFBG temperature sensors were designed and fabricated.The temperature sensing characteristics and stability of the two types of sensors in high-temperature environments were investigated.The results showed that the tube-shaped temperature sensor had higher temperature resolution,while the spherical temperature sensor exhibited better high-temperature stability.By utilizing an array of RFBG,the temperature distribution monitoring of the inner wall of a cylindrical metal container was realized,confirming the feasibility of using RFBG for temperature detection in high-temperature scenarios.