Research On High Sensitivity Displacement Sensor Based On Slow Light In Fiber Bragg Gratings

With the development of science and technology,micromachine is widely used in microelectronics,military,industry,aerospace,precision instruments and other fields.The demands for micromachine in numerous areas promote the development of micro displacement detection technology.The sensors which are based on Fiber Bragg Grating(FBG)with small size,anti-corrosion,anti-jamming,recycling,etc.,are widely used in fiber optic sensing and communications.The FBG sensor can measure displacement,but its application in the field of precision measurement is confined by low sensitivity.On the edge of the bandgap in a FBG narrow transmission peaks,light is reflected back and forth numerous times and a slice of light is transmitted,but other slice of light is reflected back.These light across the periodic structure experiences a large group delay.It indicates that structural slow light exists in the FBG and the sensitivity of the FBG is expected to be significantly enhanced by slow light technology.Therefore,the thesis presented a high-sensitivity micro displacement sensor based on slow light in the FBG,which obeyed the traditional grating sensing technology.Furthermore,the thesis demonstrated a micro displacement sensing system,and each performance of sensors was evaluated.This thesis focused on high-sensitivity micro displacement sensing system with numerical simulation and experimental data analysis.The purpose of this work include:Firstly,the characteristics and mechanism of generating slow light in the FBG were analyzed with theoretical research and numerical simulation.Meanwhile,a model of different types of gratings was developed with coupled-mode theory and transfer matrix,then slow light characteristics of different structural parameters and various types of gratings were observed,and the influence of structural parameters to FBG slow light was studied.In addition,a reasonable structural parameters of the FBG was determined for experiments behind.Secondly,slow light measuring system was designed for detecting delay in the FBG at different wavelengths,and the PC data acquisition interface was completed to achieve automatic control.Besides,slow light wavelength corresponding to the maximum delay was locked for improving the sensitivity of micro displacement sensorThirdly,based on investigation of basic theory of the FBG sensor,a practical micro displacement sensing method with slow light technology was demonstrated.At the same time,micro displacement measuring system was designed for displacement measurement experiment,and sensing characteristics were analyzed.In addition,the measurement range of this system was 60?m,the resolution 66.3nm,the sensitivity 15.0786mW/mm,and its sensitivity was up to 13 times higher than that of FBG displacement sensors.It was confirmed that FBG could generate slow light by theoretical and experimental analysis,and the sensitivity of micro displacement sensor was improved with slow light technology.Unfortunately,there are still some advantages,such as the unsteady of the light source power,sensor size and micro machining which needs a further consideration.