Hybrid ring-tree WDM/TDM-PON optical distribution network

Recent proposals for next generation FTTH PONs add the WDM dimension to the current TDM G/E-PONs, to reach an order of magnitude increase in terms of served bandwidth and number of served users. It is usually performed by introducing a trunk WDM MUX, replicating the tree topology. In search of higher scalability and trunk protection, an alternative implementation of the hybrid WDM/TDM-PON consists of the organization of the optical distribution network (ODN) as a WDM bidirectional ring with cascadable passive Add&Drop remote nodes (RN) connecting the TDM access trees, as proposed in the FP7 SARDANA project. This can be considered as a transparent passive approach of what is today known as Metro-Access convergence. With such architecture, and using state-of-the-art devices that can be potentially cost-effective in this context, a number of 512-1024 users can be served at 2.5 or 10 Gb/s, guarantying a bandwidth between 100 M and 1 G per user, at distances over 60 km with proper power budget balance, splitting ratio and number of wavelengths. The access trees length is up to 20 km, inherited from current PON standards, while the ring length may span longer distances towards a metropolitan coverage. This architecture is compatible with a colourless design of the ONU, and also with pure WDM-PON.