Research On Bidirectional Transmission Without Mimo Based On WDM-MDM System

As people enter the era of information and communication gradually,the requirement of communication technology and bandwidth have become more and more urgent.Increasing the communication capacity has become a problem that people must be solved at present.Studies have shown that the transmissional capacity of communication system has approached the Shannon limit of nonlinear optical fiber transmission,nowadays,increasing the communication capacity has became the primary research direction.The space division multiplexing(SDM)technology based on the degree of freedom of space can effectively increase the transmission capacity of communication system and solve the problems that people currently face in communication and transmission.People use few-mode fiber(FMF)as the transmission medium to build a mode division multiplexing(MDM)communication transmission system,which is widely used and can effectively expand the communication capacity of the system.According to the above requirements,we designed two structures: The first one,the WDMMDM same-mode bidirectional transmission system structure was designed,analyzed the principle of mode division multiplexing and the model of bidirectional transmission,and got the bit error rate(BER)of the transmission system;The wavelength interleaving(WI)scheme was also discussed;Based on theoretical analysis,same-mode bidirectional transmission system based on wavelength division multiplexing-mode division multiplexing(WDM-MDM)without using Multiple-Input Multiple-Output technology(MIMO)was built,and the experimental results were given.In the experiment,three non-degenerate modes(LP01,LP11a/LP11 b,and LP02/LP21)are used as bidirectional transmission channels.The 12.5km OM3 multimode fiber(MMF)is used as the transmission medium,and the photonic lantern is used as a mode division multiplexer/mode division multiplexer for actual bidirectional transmission system.And analyzed the performance of some important source devices of the experimental transmission system.The value of the transmission loss(Loss),transmission crosstalk(Crosstalk)and bit error rate(BER)of the experimental system are measured.According to theoretical analysis,we can know that the average value of transmission loss of the system is-11 d B,the average value of transmission crosstalk is-29 d B,and the BER is lower than the the limit of forward error correction(FEC-Limit),in single-way forward/reverse transmission,when the BER of the three signals reach the FEC-Limit threshold,the values of received power sensitivity are-17 d Bm/-17 d Bm,-16 d Bm/-15 d Bm and-15 d Bm respectively /-14 d Bm.In bidirectional transmission,when the BER of the three signals reach the FEC-Limit threshold,the values of received power sensitivity are-14 d Bm/-14 d Bm,-13 d Bm/-13 d Bm,and-12 d Bm/-12 d Bm respectively,we can indicate that the power penalty caused by bidirectional transmission is 3d Bm,the result is basically consistent with our theoretical analysis.The result shows that the transmission system built in the experiment has the characteristics of good performance,simple structure,low cost and so on,what's more,the capacity of transmission system has been doubled.The second structure,in order to improve the transmission system performance,the bidirectional transmission system based on WDM-MDM is further optimized.Under the condition that the total communication capacity of the WDM-MDM bidirectional transmission system is not affected,this paper designs a WI scheme.Adjacent channels in the system are offset by 1/3 WDM channel spacing,demonstrating the bidirectional WI transmission of LP01 and LP11 on the 12.5km OM3 MMF.The results show that in the absence of MIMO equalization,the WI scheme can significantly improve the performance of the same-mode bidirectional transmission system.