In a series of two articles in the Journal of Optical Communications and Networking1,2 , members of FSAN (Full-Service Access Network) and the standardization body for NG-PON2 (ITU-T Study Group 15, Question 2) give insights into the recently approved ITU-T G.989.2 recommendations. Apart from relevant technical details, the rationale behind these recommendations also is explained. NG-PON2 is a successor of the G-PON and XG-PON standards, which specified transport of 2.5 Gb/s and 10 Gb/s data signals in passive optical networks. It extends the previous standards to higher system capacity with a target capacity of at least 40 Gb/s. It is the first standard in optical access systems that recommends use of multiple wavelengths. For this, hybrid time- and wavelength-division multiplexing (TWDM PON) and/or virtual point-to-point connectivity on a wavelength basis (PtP WDM-PON) are incorporated. One specialty of NG-PON2 is that it supports legacy infrastructure, which is based mostly on power-split passive optical networks. This enables backward compatibility with the significant installed base of access fiber infrastructure. However, NG-PON2 also supports use of novel wavelength-split optical distribution networks. This allows much higher aggregate capacity using 40 to 80 WDM channels.
The second article in this series concentrates on system design and technology feasibility. Significant parts have been devoted to the multi-wavelength capability and especially the automatic wavelength tuning of the optical network units (ONUs) at the end users. Tunability of the ONUs may not only be required on the transmitter side, but also for the receivers to filter the appropriate wavelength in the case of a power-split infrastructure (broadcast). This also requires management and control, which is facilitated by an auxiliary channel. Finally, the authors analyze feasibility from the technological point of view and discuss new and challenging subsystems in depth.
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