Research On High-capacity FBG Demodulation Technology And System Based On Optical Frequency Domain Reflection

The rapid development of fiber Bragg grating(FBG)sensing technology in recent years puts forward higher requirements for the multiplexing capacity and spatial resolution.The paper uses FBG with the same Bragg wavelength and the 0.1% reflectivity to build sensor network,reducing the nature interference from the same wavelength FBG,realizing the construction of high-capacity FBG sensor network.The demodulation system of FBG sensor network is constructed based on optical frequency domain reflectometry(OFDR)technology.The high-capacity and high-spatial density FBG sensor networks high-precision demodulation can be realized by eliminating the crosstalk beat between the same wavelength,and compensating laser tuning nonlinear and calibrating laser tuning rate.The followings are main research contents:(1)Analysis the working principle of FBG sensors,including strain and temperature characteristics.Research on the influence of spectrum shadow and multiple reflection effect about multiplexing capacity,calculate the multiplexing capability under different reflectivity with a simulation tool.(2)From demodulated position information and wavelength information to analyze the principle of FBG sensing system based on OFDR.From the optical path construct,hardware design and algorithm analysis to designed and build FBG sensing system based on OFDR,achieve location information and wavelength information of each FBG in the high-capacity FBG sensor network.(3)Several methods are proposed and validated to improve system performance and to eliminate the impact of the crosstalk beak between the gratings on demodulation system.By adding the delay fiber to separate the sensor beat signal and the crosstalk beak signal in frequency domain and joining high-pass filter to filter the crosstalk beak signal in the time domain,the signal to noise ratio of sampling signal was improved.A method is proposed to achieve the laser tuning of nonlinear compensation.The spatial resolution has improved ten thousand times after compensated,reducing the request of original method on laser coherence length performance though multiplication algorithm and resampling algorithm to improve reference light path method.A method to precisely measure the laser tuning speed was put forward.By using the features of Fabry-Perot etalon resonant peak interval constant,to accurately measure the tuning speed was achieved,therefore,system wavelength demodulation accuracy was improved a lot.(4)In order to further expand the system multiplexing capacity,this research combines wavelength division multiplexing and frequency division multiplexing to build FBG sensor network,achieving the simultaneous demodulation of a single optical fiber that contain two groups of different wavelengths of 600 fiber grating position information and wavelength information.The experiment verifies that different wavelengths of fiber gratings in this system do not affect each other.