| In recent years,the pace of information society has accelerated,with the rapid development of emerging businesses such as big data,cloud computing and mobile internet,the demand for network bandwidth and communication capacity has been grown.With the higher requirements of the mobile terminal are put forward continuously,there is higher demand on the transmission rate and system capacity of the communication system.Therefore,more and more people pay attention to the optical communication because of the the prominent advantages.The high-speed and large-capacity optical fiber communication system will be the trend in the future.Such as dense wavelength division multiplexing,high-order modulation,polarization multiplexing and so many technologies are applied into the communication system,so the transmission capacity has been enhanced,the transmission distance and spectrum utilization has been improved,which provides a solid foundation for the development of next generation communication network.Space-division multiplexing(SDM)technology,a new technology that can greatly improve the transmission capacity of communication system,has drawn people's attention.SDM carries signals separately by using different modes in a multi-mode fiber and increases the degree of freedom of the system by applying multiple transmission channels in multi-core fiber,in which it can substantially increase the system capacity.Multi mode fiber has a larger mode field than single-mode fiber,so the non-linear effect is weaker,and it can provide signal transmission with large capacity.Utilizing multiple orthogonal modes in multi-mode fiber as the new degree of freedom of optical transmission system can not only increase the multiplexing dimension but also effectively improve the transmission capacity and spectral efficiency of the communication system.There are several cores in multi-core fiber,and with different structures of multi-core channels can reduce signal interference.Every core can serve as separate transmission channel,so the signal can be transmitted in each core independently,which be able to enhance the capacity of system.The structure of multi-core fiber can be adjusted according to the demand of signal transmission,and nonlinear effects of multi-core fiber is less,at the same time the mode field area is larger than single-mode fiber,as a result,multi-core fiber show a better performance in improving system capacity and spectrum utilization.However,in the actual transmission of the multi-mode optical fiber,there will be bending of the fiber and uneven distribution of the refractive index during manufacturing and laying of fiber,as a result,mode coupling may occur between the different modes.Besides,the transmission speed of each mode is different,there will be mode dispersion between the modes.Mode coupling and mode dispersion will both bring the influence to the signals,so the the cdigital signal processing is essential to restore the signal.This paper studies the components of multimode multi-core optical transmission system,and analyzes the the function of the key modules in the system.The transmission model based on multi-mode multi-core optical transmission system is established,and the theoretical analysis is given.Meanwhile the digital signal processing part in the receiver is studied.The main innovations of this paper are as follows:First,this paper studies the optical transmission system based on multi-mode fiber and multi-core fiber.Including the composition of the system,the function of each module,the key technologies used in the system such as multi-mode optical fiber optical transmission system mode multiplexing/demultiplexing,mode conversion,the connector in multi-core fiber transmission system,multiplexer/demultiplexer and so on.In addition,this paper establishes the transmission model based on multi-mode multi-core transmission system,and conducts a theoretical analysis of the factors that may affect the signal such as mode coupling,dispersion between modes,and gives derivation process of the formula.Furthermore,this paper shows the research and analysis of the structure of MIMO equalizer in multi-mode multi-core transmission system.The paper also studies the commonly used adaptive algorithms,and shows the results analyzed and compared of the simulation figure.This paper uses an adaptive step RLSCMA algorithm,this algorithm has faster convergence and tracking performance,the overall performance is better. |
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