Study On The OTDR Performance Improvement Methods

The Optical Time Domain Reflectometer(OTDR)is a widely used detection device in optical fiber communication systems.With the rapid development of optical fiber communication systems,the length of optical fiber links and the complexity of optical networks have been greatly improved.When maintaining and detecting such an optical communication network,the conventional OTDR cannot meet the requirements.It is necessary to improve the performance of OTDR and develop a new OTDR with high dynamic range and high resolution.In this paper,based on the requirements of improving OTDR performance,we propose an OTDR method based on short-time fractional Fourier transform(STFrFT)and digital linear frequency modulation(DLFM),which is called DLFM-OTDR.DLFM-OTDR can overcome the contradiction of traditional OTDR between spatial resolution and dynamic range,and improve the spatial resolution and dynamic range of OTDR.The main content of the thesis includes:(1)Setting out the basic working principle of OTDR and introduce the main technical indicators of OTDR.(2)Introducing a pulse encoding OTDR method,and the performance of the pulse encoding OTDR is analyzed by simulation and verified by experiment.The experimental results show that the pulse encoding OTDR can effectively improve the dynamic range of the traditional OTDR.However,the improvement of the dynamic range is proportional to the square root of the code length.At the same time,the pulse encoding OTDR will generate side lobes at the bottom of the strong reflection peak,affecting the resolution of the event measurement.(3)Introducing the fractional Fourier transform(FrFT),fractional Fourier filtering and STFrFT.Then the DLFM-OTDR based on STFrFT and DLFM is proposed and its working principle is elaborated.In addition,the effect of the window function of the STFrFT on the performance of DLFM-OTDR is studied.(4)Implementing the DLFM-OTDR development board based on a field programmable gate array(FPGA)and a digital signal processor(DSP).The DLFM-OTDR method is then tested experimentally.The experimental results show that the dynamic range is improved by 7 dB and the spatial resolution is increased by about 10 times compared with the conventional OTDR.Finally,the experiment of DLFM-OTDR applied in the submarine cable system is carried out.The experimental results show that the DLFM-OTDR can accurately measure the Fresnel reflection peak at the erbium-doped fiber amplifier(EDFA)and the connection point.