Research On Compensation Technology For Mode Division Multiplexing System With MDL

With the information age coming,the internet businesses,clould computing,IPTV,huge data centre as the representative of the consumptive businesses coming forth,the data traffic surging.The single mode fiber as the transmission media of backbone network,its capacity has approaching to the Shannon limit,mode-division multiplexing(MDM)technology based on few-mode fiber comes into being.In FMF,the orthogonal modes of FMF are used as independent channels to parallelly transmit data streams,the capacity of a MDM system is proportional to the number of modes ideally.There are some special impairments in FMF such as: mode coupling(MC),differential mode group delay(DMGD),mode dependent loss(MDL)and so on.Where MDL would seriously damage the system performance.Thus,we should equalization the signal at the receiver to recover the transmit signal.In this paper,after modeling the MDM system and analyzing the impairments,we set up the 6 ×6 MDM simulation system based on FMF and compensate MDL in two DSP ways.The main innovative points in this paper concentrate in two aspects.1:We proposed using successive interference cancellation(SIC)algorithm to compensate MDL.For MDL would lead huge different receive power for different modes,the equalization algorithms can not detect the transmit signal,we can see MDL as power crosstalk.By SIC algorithm,we first detect the maximum power signal and then reduce the maximum power signal interference to other signals.Then detect the second power signal,until all signals detected.For large power signal can result in big crosstalk to other signals,by canceling crosstalk from large power signal to small power signal to realize the aim at averaging the receive power.With the MDL at 10 d B,DMGD at 9 ps/km,coupling strength at-5 d B,the optical signal to noise ratio(OSNR)of the SIC-MMSE algorithm is 3 d B improved than that of MMSE algorithm at a transmission distance of 1200 km.2:We proposed lattice reduction algorithm to compensate MDL.When DMGD exist in system,the transmission matrix dimension is too large,leading lattice reduction algorithm failure.Thus,we use OFDM module to reduce the transmission matrix, transform the large dimension transmission matrix to a set of small dimension matrixes.MDL seriously deteriorates the orthogonality of the transmission matrix,at the moment the transmission matrix turns to be ill-condition matrix,resulting the receive signal has great perturbations.Thus,we adopt lattice reduction as an effective mathematical tool,by searching a new matrix which shares the same lattice space with the original matrix but with better orthogonality.We use the new matrix to replace the original matrix to detect the transmit signal.In strong mode coupling,after lattice reduction algorithm,the average condition number of transmission matrix reducing about 6 d B,OSNR plenty reduced 3.1 d B.