Research On The Key Technologies Of Coherent OTDR

With the development of optical communication technology,optical fiber has provided unimaginable transmission bandwidth for communication networks and has become the most important transmission means of information networks.At present,both the land and the sea have formed huge optical networks in the world.With the development of such technologies as erbium-doped fiber amplifier,Raman fiber amplifier and forward error correction,ultra-long-distance optical fiber communication has been widely developed.In the high-speed communication,long-distance non-relay communication is achieved,the cost of the relay station can also reduce the network maintenance cost,and also need to be applied to the ultra long-distance optical fiber communication in some special occasions,for example,the communication between islands and islands.At the same time,EDFA with WDM technology is widely used in the intercontinental communications network construction,some countries and regions and the Asian continent without land connected to the submarine cable to become a cost-effective network connection form,China’s communications lines to the United States,80%above rely on submarine cable.In the optical fiber communication,once the optical fiber is broke,the communication will be interrupted,especially the submarine cable between countries will break the communication,which will affect the communication in the whole area and will have huge social impact and economic loss.It is the key to solve the above problems to guarantee the stability and security of optical fiber links and timely and effectively grasp the status of optical links,especially the link status information of ultra-long-distance optical fiber links and submarine optical cables.Monitoring ultra-long distance and multi-span long span WDM optical fiber submarine cable monitoring requires large dynamic range,to achieve large dynamic range,Optical fiber monitoring are generally used coherent OTDR scheme,coherent OTDR receiver apply coherent detection,with high receiver sensitivity,it will greatly increase the dynamic range of OTDR,we can monitor the longer fiber length.Coherent OTDR combined with EDFA online amplification can be applied to multi-span long-span wavelength division multiplexing system to achieve multi-span transmission submarine cable monitoringThis thesis focuses on the key technologies of coherent detection of large dynamic range coherent OTDR to achieve independence of polarization and other optical fiber monitoring schemes in multi-span long-span wavelength division multiplexing system.The main research and design work is as follows.1.In order to achievesignal light and local light polarization independent of coherent detection,the scheme based on the X-coupler polarization-independent coherent OTDR is designed and the main influencing factors of the scheme performance are analyzed theoretically.In the typical value of thermal noise,the local oscillator optical power is 15dBm,the peak power of optical fiber detection signal is 15dBm,the detection signal pulse width is 20μs,and the receiver bandwidth is small,digital low-pass filter takes 100 kHz,theoretical analysis scheme dynamic range up to 50dB.2.We comprehensively compared and analyzed the feasibility of the three mainstream optical communication simulation tools suitable for the simulation scheme,we established MATLAB as a simulation tool,and programmedthebased on X coupler coherent OTDR simulation platform by MATLAB,we completed by MATLAB softwarebased on X coupler coherent OTDR simulation platform simulation to verifypolarization independence of the scheme,the influence of the key parameters on the dynamic range and event resolution are compared with the theoretical results.The simulation results are consistent with the theoretical results.3.The offline experiment system based on the X-Coupler coherent OTDR scheme is completed and set up.The key parameters of the coherent OTDR scheme are experimentally verified in the offline experiment system.The key parameters include the pulse width of the probe signal,the peak power of the probe signal pulse,resolution of the experimental results and the theoretical results were compared to the experimental conditions to take the local oscillator optical power of 14.5dBm,the fiber detection signal peak power of 15dBm,pulse width of 20μs,the receiver bandwidth of 25GHz,the experimental OTDR dynamic range of 31dB.The main reasons for the experimental dynamic range of only 31dB are:1)the responsivity of the coherent receiver is poor;and 2)the receiver’s bandwidth is too large and the sensitivity of the receiver is poor.Under the experimental system receiver parameters,the experimental results and the theoretical analysis results are basically the same.4.The necessity of optical fiber link monitoring in multi-span long-span wavelength division multiplexing system is analyzed.The design of optical fiber monitoring scheme for multi-span long-span wavelength division multiplexing system is completed.The multi-span long span fiber chain road monitoring made a theoretical analysis and deduction.The simulation platform of the scheme was completed by MATLAB programming.The gain of EDFA was 30dB,the noise figure was 5dB,the length of each span was 150km,and other conditions same as above "1".The simulation of fiber link monitoring of long span multi-span WDM system is completed on the simulation platform.Simulation results show that this scheme can monitor 100 × 150km optical fiber link.