Research On Key Technologies To Improve OFDR Performance

Optical frequency domain reflectometer(OFDR)is a new sensing method in the field of optical fiber sensing.It started late,but it can be widely used in aerospace,electronic power,geological disasters and other fields,and realize the measurement of temperature sensor,strain sensor and birefringence.However,OFDR system still has some shortcomings in testing distance and long-distance spatial resolution.How to improve the test distance of OFDR,and how to improve the spatial resolution in the case of long-distance is still a difficult problem.This paper starts with the key issues affecting the spatial resolution and test distance of OFDR,analyzes the structure of OFDR system in detail,and improves the structure.At the same time,it studies the influence of light source nonlinearity and its elimination methods.Through formula derivation,simulation verification,experimental analysis and other research methods,the performance of measurement distance and spatial resolution of OFDR is improved.The main contents of this paper are as follows:1.The theoretical model of optical frequency domain reflectometer is established.The theory of Rayleigh scattering,the principle of optical heterodyne detection and the basic principle of OFDR are analyzed,and the expression of beat frequency signal is derived.Through the detailed analysis of the expression,it is concluded that the key factor affecting the OFDR system is the non-linear phase changing randomly with time.2.The nonlinear effect of light source and its compensation method in OFDR are studied.The principle and difference of hardware compensation method and software compensation method are analyzed in detail.In the software compensation method,this paper analyzes the declination filter method and one-dimensional interpolation method,and deduces the formula of the declination filter method.Finally,the reason of polarization fading effect and its eliminating method are analyzed.3.Based on the Mach Zehnder interferometer and polarization polarization polarization structure,a frequency domain reflection system is built.Through software simulation and experimental analysis,it is concluded that the compensation effect of one-dimensional interpolation method is better than that of declination filter method when the test distance is less than 500m,and the compensation effect of declination filter method is better when it is greater than 500m4.The shortcomings of the original system structure are analyzed in detail and optimized.By improving the system structure,the loss is reduced,the optical path is simpler and the experiment operation is more convenient.Experimental analysis of the optimized system:under the test distance of 2590 meters,the spatial resolution after one-dimensional interpolation compensation has reached 69 cm,which has been unable to locate accurately in the original system;the spatial resolution after compensation by the declination filter method is about 1 m,which is twice as high as the original system.