Study On Mode Division Multiplexing Technology In Few-Mode Fiber

With the growing popularity of personal mobile and fixed broadband ICTservices, the rapid development of the Internet and data centers IT services, thedemand for network bandwidth has reached an unprecedented height in currentinformation society.In order to resolve the enormous pressure to the optical transportnetwork caused by the emerging bandwidth consumption business, a variety ofmethods has been proposed to promote the capacity of optical network. Single modefiber may reach the foreseen bandwidth exhaust due to the inherent nonlinear effectsof the single mode fiber. Therefore, it is vital important to explore a suitable opticaltransport technology to permanently resolve the bandwidth limit of single mode fiber.The mode division multiplexing based on few mode fiber come into being in thisbackground. The limited and stable modes are used as independent signal channelsfor mode division multiplexing technology, which can exponentially increase thesystem capacity and the spectral efficiency. The paper is based on such backgroundto study the mode division multiplexing technology in few mode fiber.As mode multiplexing in few mode fiber is an emerging technique, this paperwill focus on the the most basic configuration and technologies of modemultiplexing. The mode characters in few mode fiber are analyzed by solving thederivation of Maxwell’s equations. The orthogonality of modes in few mode fiber isderived rigorously by using Waveguide Optics Theory, which is the physical basis ofmode multiplexing. Three different methods are used to model mode multiplexingsystem and the characteristics of various modeling methods are analyzed. Severalkinds of regular mode multi/demultiplexers are introduced in this paper. A modemulti/demultiplexer based on asymmetric planar waveguide is designed, and thedesigned device also has a mode conversion function. By using beam propagationmethod simulation analysis, the designed device is proved to have a good modemulti/demultiplexing performance. The system performance is analyzed through thesimulation platform to analyze the affects of different system impairments on systemperformance. The main efforts in this paper are as follows:Firstly, as the few mode fiber is the physical basis in mode division multiplexing system, the mode characters in few mode fiber are analyzed by solvingthe derivation of Maxwell’s equations. And also simulate the spatial light fielddistribution of several modes in few mode fiber. As the most fundamental theoreticalbasis of mode multiplexing, the orthogonality of fiber modes is derived in this paper.Secondly, the mode division multiplexing system is analyzed theoretically byperform mathematical modeling approach. The coupled mode theory model,nonlinear Schr dinger equation model and matrix propagation model are introducedand analyzed for modeling the simulation system of mode division multiplexing.Then several key technologies in mode multiplexing are briefly described.Specially,the digital signal processing algorithm and processes in coherent receiver areillustrated detailed, which is very important for signal process in the subsequentsimulation system.Thirdly, as the key device in mode division multiplexing system, modemulti/demultiplexer is studied in this paper.the principle and properties of severalkinds of regular mode multi/demultiplexers are introduced and analyzed. A modemultiplexer/demultiplexer based on asymmetric planar waveguide is designed, andthe designed device also has a mode conversion function, which makes it atwo-function device. After simulation analysis by beam propagation method, thedesigned device prove to have a good mode multi/demultiplexing performance andalso have good advantages of miniaturization and integration, which makes it anexcellent mode multi/demultiplexer.At last, a mode division multiplexing system in two-mode fiber is built by usingthe combined approach of nonlinear Schr dinger equation and matrix propagationmethods. The system performance is performed using direct detection and coherentdetection and analyzed under different system impairments, such as mode couplingand differential mode delay. The methods to improve system performance areproposed to make preliminary recommendations for future research.