Mode Division Multiplexing Transmission Based On Few Mode Fiber

With the rapid development of various bandwidth-consumption services,including machie-to-machine traffic,cloud computing,high-definition mobile video,real-time communication,the amount of traffic arising in current backbone network has been growing exponentially over the past two decades.Those services lead to the increase of the network interface rate close to the transmission rate of data center and high-performance computer,at the order of Tbit/s.However,traditional standard single mode fiber(SSMF)based communication system,limited by the nonlinear Shannon limit,can't support such huge bandwidth requirement.Since all possible physics dimensions of optical signal,such as wavelength,time,frequency,polarization and quadrature,have been exploited,spatial is the only dimension not already exploited for optical fiber transmission.Therefore,space division multiplexing(SDM)has stimulated worldwide research interests,due to the possibility for a substantial increase of transmission capacity.These thesis focuses on mode division multiplexing(MDM)transmission system based on few mode fiber(FMF).Several topics include the basic theory of MDM,the management of FMF link,the optimization of high order modulation formats,the equalization enhanced phase noise(EEPN)in MDM transmission,and MIMO equalization techiniques were investigated.The main results are summarined as follows:(1)After explanation of several basic concepts,such as vectorial modes,linear polarization(LP)mode,and mode group,the concept of Gram-Schmidt mode is put forward for the ease of general descriptions.Based on this concept,the orthogonal angular momentum multiplexing(OAM)can be treated as a specific case of mode division multiplexing(MDM),and the effect of mode coupling can be dealt with the transformation between Gram-Schmidt modes together with the modification of propagation constants.The statistic characteristic of group delay spread and its influence on the receiver complexity is theortically investigated.(2)An elliptical core FMF(e-FMF)for MIMO-less transmission was designed,fabricated and characterized.Since the degeneration of spatial mode is broken,the mode coupling among spatial modes is successfully suppressed.Consequently,each mode channel is independent without mode coupling,such kind of FMF can be used for MIMO-less MDM transmission.Furthermore,a differential mode group delay(DMGD)management for the FMF link is proposed with the help of cyclic mode converter(CMC).The fabrication error of CMC and the random perturbation influence on the transmission performance are investigated.(3)Various advanced modulation formats arising in the FMF transmission is investigated.The result show that the quadrature duobinary(QDB)format can improve the spectral efficiency of MDM with a relatively low cost.Moreover,with the assistance of post-filter and Maximum Likelihood Sequence Detection(MLSD)technique,the MDM-QDB transmission system has better tolerance of narrow bandwidth filtering effect and group delay induced impairment.(4)The equalization enhanced phase noise(EEPN)effect arising in MDM transmission is investigated.The result show that the EEPN arising in the FMF transmsison is due to not only the interaction of local oscillator(LO)laser and electronic dispersion compensation but also the interaction of LO laser and DMGD.A post-filter and MLSD scheme is employed to enhance a system impaired by EEPN.(5)The equalization performance of different step-size on T/2-spaced MIMO was investigated.The result show that the MIMO based on constant module algorithm(CMA-MIMO)has a larger tolerance of step-size and fast convergance than the MIMO based on least mean square algorithm(LMS-MIMO)both in time domain equalization(TDE)and frequency domain equalization(FDE).In particular,the FDE can reduce the computational complexity than that of TDE,but has a smaller step-size tolerance than the TDE.