Research On Key Technologies Of High Accuracy Fiber Accelerometer

With the development of fiber Bragg gratings manufacturing technology and the adoption of various doped fiber as gain medium,fiber laser sees a promising future and a vast range of applications.The electromagnetic interference resistance,low loss and high sensitivity to ambient disturbance of fiber,combined with the high signal-to-noise ratio,and possession of various sensing parameters of fiber laser make fiber laser sensor attractive to researchers.Among different kinds of fiber laser,distributed Bragg reflector（DBR）fiber laser shows its excellent performance in many sensing areas,such as the measurement of high accuracy vibration,pressure and strain,due to its compact size,intense signal and stability.Accelerometer is often used in seismic wave detection,imaging system and structure health monitoring system,where accurate detection and recovery of micro vibration signal is demanded.In this paper,high accuracy accelerometer is manufactured with short cavity DBR fiber laser and the beat frequency generated by orthogonal polarization modes in DBR fiber laser is utilized as the sensing element.This paper is organized in the following way:（1）Current studies of accelerometer are introduced,especially the fiber based accelerometer.（2）Basic DBR fiber laser structure and principle are introduced.Fiber Bragg grating mode coupling theory and transmission spectrum of Fabry-Perot etalon are implemeted to analyse the optical output characterisitics of DBR fiber laser.The formula of DBR fiber laser beat frequency lateral force sensitivity is deduced utilizing elesto-optical effect.Experiments on lateral force and temperature sensitivity of DBR fiber laser beat frequency are carried out.（3）DBR fiber laser beat frequency stability is studied.Self-pulsation in the time-domain of beat frequency is discovered and its relationship with beat frequency fluctuation is inspected for the first time.“Self-injection”method is proposed to eliminate the self-pulsation in DBR fiber laser to enhance beat frequency stability,both theoretical analysis and experimental verification are conducted.And a significant reduction of beat frequency fluctuation from 800kHz to 8kHz is realized.（4）High sensitivity cantilever-mass structure accelerometer transducer is designed.The theoretical sensitivity and natural frequency of the accelerometer structure are deduced.By comparing the theory and the simulation results of finite element analysis by software ANSYS,an optimized structure is proposed.（5）An integrated accelerometer system is established.The demodulation system utilizing LABVIEW programming is introduced.The response of accelerometer to vibration is examined.Results show:This cantilever-mass structure accelerometer is suitable for demodulation of acceleration from 20Hz to 200Hz,its sensitivity is around 1.9732GHz/g,and the accuracy of this accelerometer is2?10^-5gin experiment,the theoretical accuracy of this accelerometer can reach4?10^-6g,which is applicable to high accuracy small vibration acquisition.