| After several decades of development, fiber optic communication technology has gradually extended from backbone networks and metro networks to access networks. Currently, the mainstream technologies of optical access networks are EPON and GPON, which are based on time-division multiplexing. But with the emergence of high bandwidth network services and the increasing requirement of access bandwidths, the traditional TDM-PON will not meet the demand of future access networks. Wavelength-division multiplexing passive optical networks, which will replace TDM-PON, will become the best candidates of future access networks.The thesis mainly studies the system architechture and multicast/broadcast technologies of remodulated WDM-PON, in which remodulated components are used in an ONU to replace lasers. In the first place, the basic knowledge of optical access networks and different system structures of WDM-PON are introduced, and then typical remodulation structures of WDM-PON are analyzed. In the second place, a novel modified NRZ signal format is presented. By combing modified NRZ signal format with remodulation WDM-PON, multicast function is realized. Finally, the performance limitations of WDM-PON and different existing wavelength conversion technologies are analyzed, and a semi-passive optical distribution network is designed to realize broadcast function.Optisystem software is used to do numerical simulations in this thesis. Firstly, the model of remodulation WDM-PON is established. Based on this, multicast WDM-PON with modified NRZ signal format is emulated. The results show that the optical signal with low extinction ratio can improve the performance of the upstream and downstream data, if multicast function is disabled. Finally, the paper studies the system structure of semi-passive optical distribution network. The results drived by simulation demonstrate that the performance limitations of remodulation WDM-PON can be eliminated and it can extend the network transmission distance. |
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