Research On Photoelectric Detection System For Ultra-weak Fiber Bragg Grating Demodulation

With the development of optical fiber sensing technology,optical fiber sensor is favored for its superior performance,it has the advantages of small size,light weight,anti electromagnetic interference,anti-corrosion,high sensitivity,measurement bandwidth,and long distance between detection electronic equipment and sensor,it can bend and layout can be more flexible,suitable for complex environment and not limited by space,the excellent performance makes the optical fiber sensor have a wide application prospect.With the successful fabrication of a new generation of ultra-weak Fiber Bragg grating,optical fiber sensor network is developing towards the direction of large capacity,high precision,fast response and long distance.The ultra-low reflectivity of ultra-weak FBG improves the multiplexing ability and transmission distance of FBG sensor network,but it also brings problems that the reflected signal is weak and difficult to measure,low detection accuracy and the result of demodulation can not meet the requirements of practical application.Study on the detection method of weak reflection signal of ultra-weak FBG,improve the detection accuracy enhancing the practical ability of ultra-weak FBG is a hot research direction at present.This article starting from the study of demodulation mechanism of ultra-weak FBG,using photoelectric detection circuit to measure weak signal,research on the principle and type of noise produced by photoelectric detection circuit,using improved variable step LMS algorithm to deal with the noise of photoelectric detection circuit,presents a design method of photoelectric detection circuit which is suitable for photoelectric detection circuit for the extraction and detection of ultra-weak FBG reflected signal.The main research contents are as follows:(1)Research on fiber grating sensing technology.This paper combine the development status of fiber Bragg grating sensing technology at home and abroad,describe the principle of FBG sensing,analysis and comparison of advantages and disadvantages of several commonly used FBG demodulation and multiplexing technologies,provide theoretical basis for networking and demodulation technology research.(2)Aimed at the problem that weak reflection signal is difficult to collect,propose to use photoelectric detection circuit to collect signals,ensure that weak signals can be accurately extracted,realize high precision demodulation.Study on the mechanism and source of noise in photoelectric detection circuit,analyze noise types and establish noise mode.(3)Introducing various components used in photoelectric detection system,Study the main influencing factors based on the noise formula of the core device,choosing InGaAs PIN photodiode as photodetector,using low noise AD711 high speed single chip as operational amplifier,complete the design and construction of hardware circuit.(4)The LMS algorithm is applied to the photoelectric detection circuit of ultra-weak FBG reflection signal extraction to remove noise.Analyzing the theory of LMS algorithm,using correlation characteristics to improve variable step LMS algorithm,using improved variable step LMS algorithm to deal with the noise of photoelectric detection circuit,achieving good results,meet the requirements of ultra-weak FBG demodulation.(5)Design and build a temperature test system to test the performance of photoelectric detection system.The test results show that the measurement wavelength error of photoelectric detection circuit is within ± 5pm.The system has good detection ability for reflected light signal,improve the accuracy of detection,meet demodulation requirements.