Research Of The Mode Division Multiplexing Direct Detection Communication System Based On Few-mode Fiber

We are in an era of emerging technology and iteration.5G communication technology has begun large-scale trial operation,and AI,automatic driving,cloud services and other technologies have also emerged.The development of these new technologies all depends on the increasing amount of data,so it also puts forward higher requirements for the transmission rate of our current optical network.In more than half a century since the advent of optical fiber communication,the transmission rate of optical communication network has been greatly developed.However,the non-linear effect of standard single-mode fiber itself has determined that the transmission rate cannot continue to be greatly improved,and the current optical network has gradually approached its Shannon limit.In order to break through this limitation,researchers began to look for more ways to expand capacity.As a kind of space division multiplexing,module division multiplexing technology has become a research hot spot.Mode division multiplexing uses several spatially orthogonal linear polarization modes as non-interference channels for communication,so it can improve the system capacity multiple times compared with the ordinary standard single-mode fiber.The direct detection communication scheme has the advantages of low cost and low complexity,so it has better practicability in the data center and other short-distance communication scenarios.But compared with coherent communication system,direct detection communication is more sensitive to mode coupling and equal interference,which is also a problem we need to solve.This paper mainly focuses on the development of the MDM direct detection communication system based on the SMF,puts forward the theoretical model of the MDM direct detection communication system based on the SMF,and verifies its feasibility from the perspective of simulation and experiment,and analyzes its performance.The main contents and innovations of this paper are as follows:In this paper,the transmission link model of MDM communication system based on SMF is studied,and the feasibility of MDM is demonstrated.The random coupling between modes and the dispersion between modes in the transmission link are studied,which lays a good foundation for the subsequent establishment of the theoretical model of the transmission system based on SMF.Based on the theoretical model of the transmission link of the few mode optical fiber,the theoretical model of the direct detection transmission system for the transmission of SSB signal is studied.In this system,the advanced modulation format of pulse amplitude modulation is used to achieve higher spectral efficiency and reduce the cost per bit.On the other hand,optical single side band modulation is used to reduce the power fading effect and double the spectral efficiency.Different solutions are proposed for the three kinds of damage caused by single side band modulation and mode coupling in the received signal of the theoretical model.The simulation platform based on the proposed theoretical model is built by using MATLAB simulation software.The feasibility of the transmission scheme is first verified by transmission simulation experiments,and the feasibility of the algorithm to eliminate the related damage is gradually verified.On the basis of the simulation results,a transmission experiment platform based on mode selective photon lantern and graded index two mode few mode fiber is built.The feasibility of the model is verified by the experiment of the direct detection transmission of the two-way single side band PAM signals with different coupling rates.The performance of the system is analyzed.