| Fiber Bragg grating?FBG?is a key component widely used in optical fiber communication and optical fiber sensing fields.The photosensitive characteristics of ordinary FBG working in a high temperature environment for a long time will gradually decline or even completely erase,thus limiting the application of FBG in the high temperature sensing field.However,Regenerated fiber Bragg grating?RFBG?formed after high temperature erasing can be generated by high temperature annealing?850?950??to work stably in a high temperature environment over 1000? with stable properties.But the mechanical strength of RFBG after high temperature annealing treatment is significantly lower than that of general FBG,which makes it difficult for RFBG to meet the requirements of engineering applications.Based on the phase mask method,this paper designs,optimizes and builds a FBG writing system,and studies the writing and performance of FBG.Based on the preparation of RFBG with good high temperature measuring effect,the axial stress of the fiber grating and the molecular composition and structure of the quartz fiber were studied,and the cause of RFBG brittleness was analyzed and deduced.The main research contents are as follows:?1?On the basis of the traditional phase mask method,the laser spot is more uniform and adjustable by adding the beam expanding system.The loss of the laser in the transmission process is calibrated,and the loss is nearly 95%.The effects of exposure energy,type of fiber and length of grid area on the spectral performance of grating are studied.The difference of photosensitivity between the hydrogen-loaded fiber and the B/Ge co-doped fiber was evaluated.The results showed that the reflectivity of FBG was 98.17% after the exposure of 38.68 J due to the difference of doping.Under the same condition,the reflectance of FBG written by hydrogen-loaded fiber is 82.98%.However,when the exposure continues to 77.36 J,the reflectance of FBG written by the hydrogen-loaded fiber can reach 99%.?2?The experimental platform for the thermal regeneration of fiber Bragg grating was built and the RFBG was tested at high temperature.The temperature sensitivity of RFBG was up to 15.6pm/?,and the linear response was good in the range of 100?1000?.The annealing program of heatregenerated fiber Bragg grating is analyzed,and the optimum annealing temperature is explored.The analysis shows that the optimal annealing temperature is between 920? and 935?.When the temperature is lower than 900?,the time from annealing regeneration to saturation is longer,which increases the uncertainty of RFBG preparation.When the temperature is higher than 950?,annealing will lead to poor spectral characteristics.Through optical fiber axial stress test and material internal component analysis,studied the performance of the fiber Bragg grating changes before and after annealing,found that the main reason for the state changes before and after the fiber Bragg grating back when annealing temperature is too high,making smaller inside the fiber orientation,and internal compressive stress and tensile stress are reduced,causing structure than the original fiber close,results in lower mechanical properties and brittleness increased.This work provides a reliable theoretical and experimental basis for improving the mechanical properties of RFBG and solving its brittleness problem.?3?By using stainless steel tube and high temperature ceramic glue to encapsulate the heatgenerated fiber Bragg grating,the temperature sensitivity of the encapsulated RFBG sensor is 14.8pm/?,which plays a good role in protecting the fragile grating area.A set of demodulation equipment was built by the existing photoelectric circuit board and AWG,and distributed temperature measurement was realized.The temperature sensitivity was 0.414?-1 at 0?20?.The temperature sensitivity at 100?150? was 0.3784?-1. |
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