The Research Of Mode Converter For Mode-Division Multiplexing

With the rapid development of communication technology,the capacity of traditional single mode fiber is close to the limit of Shannon's theorem.In order to meet the growing demand of throughput,space division multiplexing(SDM)(also known as the technology of optical fiber MIMO)was carried out.Mode division multiplexing(MDM),as one of the the most commonly technique for space division multiplexing,is the communication technology to transmit multiple different modes at the same time in a fiber core,each mode carries independent data.What's more,Mode converter is the key device of the mode division multiplexing,which become a hot research topic in recent years.Firstly,this paper studies the relationship between the ideal optical fiber mode.Through Helmholtz equations and boundary conditions of the fiber,we respectively obtained the eigenvalue equations of vector mode and scalar modes,and orthogonality can be found among modes of ideal fiber waveguide.Then using the fundamental principles of the MDM,we detailly analysis the key components of the module,and come to conclusion that the performance of the mode-division multiplexing transmission system is mainly affected by the mode coupling,mode dispersion,the performance of key components.In addition,we get coupled wave equations in Terms of the ideal mode expansion and the local normal mode expansion,and the coupling coefficient is obtained between the modes using the perturbation method,found that the coupling among modes is actually energy conversion among modes.Therefore,the mode conversion can be achieved by directionally increasing the coupling between the two specific modes,which provides the direction for the design of the mode converter.Finally,this paper puts forward a LP01?LP0m mode converter with a new structure.,which has a wide bandwidth 0.35?m(1.35?m-1.70?m,the conversion efficiency>89.97%)of LP01?LP02.The proposed converter consists of three parts:the core,cladding and annular distribution of double tapers structure.To analyze and optimize the structure parameters,the best performance of the mode converter can be obtained:when the wavelength is 1550nm,the extinction ratio is a maximum of 69.16dB,the minimum insertion loss is 0.18dB,that is the conversion efficiency of 95.94%.Finally,we analysis the influence of the number of double tapers for the mode converter performance.In the case of the best performance,the different mode converters are compared.