Study On Distributed Optical Fiber Sensor Based On Optical Frequency Domain Reflectometry

Compared with traditional electronic sensing technology and mechanical sensing technology,distributed fiber optical sensing technologies have many incomparable technical advantages.The optical fiber sensor based on the technology not only has the characteristics of small size,light weight and embeddability,but also has large dynamic range and strong anti-electromagnetic interference ability,and can be applied in harsh environments or occasions with high measurement accuracy,which has great research value.Among them,optical frequency domain reflectometry(OFDR),as a very promising technology in distributed fiber optical sensing(DFOS),has become an emerging development direction in the field of optical fiber sensing with its high spatial resolution and sensitivity.Nowadays,it is widely applied to health monitoring in the important domains such as civil engineering,communications,petrochemical and power industries.In the paper,we aim to solve the trades off between spatial resolution and strain resolution in existing OFDR-based distributed optical fiber sensing technology to improve its performance by studying the sensing mechanism of backscatter Rayleigh,nonlinear effect of laser tuning and demodulation algorithm.The main contents are as follows:1.We briefly introduce the research status of the OFDR technology,and point out the research purpose and main content of the paper.2.We study the basic theory of the OFDR system in detail,including the Rayleigh scattering generation mechanism,optical heterodyne detection technology and the theory of the OFDR,and the main factors affecting the performance of the system.In addition,we offer two methods of compensating the nonlinear frequency sweep effect of laser,consisting of hardware compensation algorithms and software compensation algorithms.3.We propose two demodulation schemes for OFDR signals,including phase demodulation algorithms and cross-correlation demodulation algorithms.In the cross-correlation demodulation algorithm,we introduce a combination of zero padding in the frequency domain and Gaussian fitting based on the least square method to improve wavelength resolution of cross-correlation.And the two demodulation algorithms are designed on MATLAB software for numerical simulation and compared in terms of spatial resolution and stability.4.We firstly analyze and select the main components in the OFDR system,and complete the experimental system.Then,we design and develop the relevant software on the LABVIEW platform,including laser frequency sweeping program,trigger data acquisition program and signal demodulation program.5.We experimentally verify the proposed cross-correlation wavelength resolution improvement method.Then,temperature and strain sensing experiments are performed to establish the correspondence between temperature and strain and spectral shift.On the basis,the two-dimensional shape sensing of the steel plate is completed by arranging and calibrating the optical fiber with a special structure.