Research On The Application Of PAM-4 In Next Generation PON

The transmission rate can be increased effectively by the 4 Pulse Amplitude Modulation(PAM4)technology because of four amplitude levels and transmits two bits of information per symbol,making it a popular transmission technology in the next generation data center.In the next generation Passive Optical Networks(PON),high-speed and large-capacity are the main demands of today's optical fiber access network,and shows that PAM4 signal is more potential than binary signals at high speeds and PAM4 transmission technology will gradually replace the original binary signals in the future PON.In the evolution to the next-generation PON,smooth upgrade and colorless ONU are two major challenges.In addition,due to the rapid growth of point-to-point data interaction,inter-ONU-communication is also a problem that needs to be solved.In the process of smoothly upgrading to the next generation PON,it is necessary to be compatible with the existing PON system and reuse the laid optical distribution network,eliminate the interference of the newly added PON line to the existing line,and realize the coexistence of the new and the old line.For this reason,a Manchester-PAM4 scheme based on line coding where combines the characteristics of Manchester and PAM4 is proposed.It not only suppresses the low frequency components,so as to coexist with the original NRZ signal,but also maintains the coding efficiency at 100%.In the future,Manchester-PAM4 can be easily changed to PAM4 which is more suitable for future PON after the next generation PON is completely upgraded.In addition,in the case of limited wavelength resources,the next generation PON can also be upgraded at the same wavelength.In the research of colorless ONU,the problem of coexistence of two kinds of signals is also involved.This paper adopts the uplink re-modulation technology based on Manchester-PAM4 to realize it.The above two schemes adopt software simulation test,the result shows that Manchester-PAM4 signal and Manchester code can reduce almost the same crosstalk,but can provide double bit rate.And compared with the binary NRZ signal with reduced extinction ratio(ER),the Manchester-PAM4 signal exhibits lower crosstalk in the coexistence scheme.In addition,in the simulation setup of uplink remodulation,the Mach-Zehnder modulator and reflective semiconductor optical amplifier were used to realize the simulation,and the influence of the downlink on the uplink signal with different uplink and downlink rate ratios was analyzed.In the research of inter-ONU-communication in the next generation PON,a physical layer network coding(PNC)scheme based on PAM4 is proposed.On the physical layer,the two ONUs that communicate with each other are combined together and then broadcast and sent.Since there is no need to use the OLT as a bridge,the efficiency of communication between ONUs is improved.Other ONUs cannot demodulate the combined data because they do not have the original data,which improves the security of communication.Considering the two cases of different optical fiber length transmission and different ONU output power differences and A 25 Gb/s full-duplex and private communication is demonstrated by simulation.The results show the feasibility of the proposed PAM4-PNC.