Study Of The Optical Wireless System Based On Mode-division Multiplexing Technology

As it has been reported,compared to that in 2014,the mobile data traffic will increase at least 10 times compared by 2019,which will probably climb up to 24.3 exabytes per month.Multiple-input multiple-output?MIMO?,based on spatial multiplexing and space diversity technology,is an essential technology of wireless communications to achieve extremely ambitious capacity goals.Several multiplexing techniques for MIMO have been proposed,such as polarization division multiplexing,wavelength division multiplexing and polarization division multiplexing.However,these approaches require relatively expensive multiplexer and demultiplexer components,which severely limit their practical application,especially for future large number of spatial streams due to a higher cost.The mode-division multiplexing?MDM?technology comes out.MDM uses different modes in the fiber as different communication channel and needs several modes to transmit signals.Nevertheless,mode coupling and loss in multimode fiber?MMF?are extremely serious.The few-mode fiber?FMF?has a relatively larger mold area,with a small number of modes,all of which modes are stable.Thus FMF is suitable to be used as the transmission fiber for MDM.Over recent years,3D-waveguide PLs supporting 3-spatial-mode(LP₀₁,2xLP₁₁),6-spatial-mode(LP₀₁,2xLP₁₁,2xLP₂₁ and LP₀₂)and 15-spatial-mode(LP₀₁,2xLP₁₁,2xLP₂₁,LP₀₂,2xLP₃₁,2xLP₁₂,2xLP₄₁,2xLP₂₂,and LP₀₃)have been developed successively,which make the MDM system flexibly upgraded to support more spatial streams without dramatically increasing insertion loss and system cost.This paper will experimentally demonstrate MDM transmission signals over 3 spatial modes of two-mode graded-index FMF employing non-mode-selective 3D-waveguide photonic lantern?PL?which directly converts three Single Mode Fibers?SMFs?into two modes(LP₀₁,LP₁₁a and LP₁₁b)of the FMF,to research on the transmission characteristics of MDM system based on the FMF.Experiments were carried out to measure and analyze the mode field distribution of transmission optical signal,the Rice factor of transmission channel and the condition number of transmission matrix.It is concluded that when the transmission fiber length increases,the condition number of the transmission channel tends to be smaller and the stochastic characteristic is switching from Rice distribution to Rayleigh distribution.It is indicated that spatial multiplexing benefits from longer fiber reach despite of higher optical loss.