Research On Mode Division Multiplexing Technology With Coherent Optical Communication

As the backbone of telecommunications infrastructure,optical fiber communication provides strong support for the continuous development of the Internet.In the past thirty years,the processing power of computer systems and the demand for broadband Internet traffic have been increasing exponentially under the guidance of Moore's Law,and this growth trend is expected to continue for a long time.According to forecasts,global mobile traffic will approach the zettabyte milestone in 2022.For my country,with the rapid development of new services such as 5G,Internet of Things,and cloud computing,the demand for large bandwidth of optical fiber communication networks will become more urgent.The current optical fiber communication system has made use of the various degrees of freedom of light waves in single-mode fibers,including frequency,polarization,amplitude,and phase.Limited by the physical characteristics of the laser light source and modulation devices,the speed increase and channel expansion have also reached bottleneck.Faced with the continuous pressure of traffic growth of various businesses,space division multiplexing technology based on spatial dimensions has emerged as the times require,and has attracted widespread attention and research in recent years.This paper aims to explore the practical application of Modular Division Multiplexing technology in communication systems.It adopts IQ modulation-coherent reception and uses mode-selective photon lanterns as mode multiplexers/demultiplexers to build QPSK-based signals.And PDM-QPSK signal modular multiplexing transmission system,measured the various indicators of the system,and analyzed the performance of the system.This article mainly does the following work:The basic composition and structural characteristics of the mode division multiplexing communication system are introduced.Then,the mode transmission characteristics under the condition of few mode fibers are theoretically deduced in the differential form of Maxwell's equations,and then the mode division multiplexing system in the mode division multiplexing system is theoretically deduced.The orthogonality of is deduced and analyzed.Finally,the key components in the current mode division multiplexing communication system are introduced in detail from three aspects:the few-mode fiber,the mode converter and the mode multiplexer/demultiplexer.Then a 6×6 modular multiplexing communication system was built.The system uses mode-selective photon lanterns and supports up to 6 mutually orthogonal modes such as LP₀₁,LP_11a,LP_11b,LP_21a,LP_21b,and LP₀₂ as independent channels to realize the signal Multiplexing transmission;then adopt the communication mode of IQ modulation and coherent detection,record the signal waveform diagram and constellation diagram of different transmission rates of 2Gbit/s and 8.5Gbit/s in each mode,analyze and compare the error characteristic curves of different transmission rates,And its impact on the performance of the communication system.The experimental results show that when the received power of LP₀₁,LP_11a,LP_11b,LP_21a,LP_21b,LP₀₂ and other modes is not less than-37.13d Bm and-35.27d Bm,the bit error rate of each signal can reach below 10^-3.Then use a polarization beam combiner at the transmitting end of the system to polarization multiplex the two QPSK signals,and transmit them through a 3×3 mode division multiplexing system.At the receiving end,perform offline digital signal processing on the received signals to achieve polarization demultiplexing.,Record the waveform diagram and constellation diagram of different rate signals such as 17Gbit/s,34Gbit/s and so on in each mode,analyze and compare the error characteristic curves at different transmission rates,and their impact on the performance of the communication system.The experimental results show that when the received power of LP₀₁,LP₁₁,LP₂₁ and other modes is not less than-33.59d Bm and-25.32d Bm,the bit error rate of each signal can reach below 10^-3.Finally,the main research content of the full text is summarized.Based on the experimental data,the optimized scheme of the modular multiplexing transmission system is proposed.Finally,the content and direction that still need to be improved and researched are discussed.