We have seen in Chapter 15 that wavelength division multiplexing (WDM) upgraded Ethernet passive optical networks (EPONs) are expected to become mature in the near term. In this chapter, we consider WDM EPONs and, arguing that the key tasks of cost reduction and design of colorless ONUs will be addressed successfully in the near term, elaborate on the question “WDM EPON – what's next?” Our focus will be on evolutionary upgrades and further cost reductions of WDM EPONs and the alloptical integration of Ethernet-based WDM EPON and WDM upgraded RPR networks. The resultant Ethernet-based optical access-metro area network, called STARGATE, was recently proposed in Maier et al. (2007) and will be described at length in the following.

Research on the interconnection of multiple (E)PONs has begun only very recently. In Hsueh et al. (2005a), multiple PONs of arbitrary topology are connected to the same central office (CO) whose transmitters may be shared for downstream transmission among all attached PONs. In An et al. (2005), a common fiber collector ring network interconnects multiple PONs with the CO whose transmitters are used not only for downstream from CO to subscribers but also for upstream transmission from subscribers to CO by means of remote modulation. Note that in both proposed PON interconnection models, any traffic sent between end users residing in different PONs has to undergo OEO conversion at the common CO (i.e., PONs are not interconnected all-optically).

RPR can easily bridge to Ethernet networks such as EPON and may also span into metropolitan area networks (MANs) and wide area networks (WANs). This makes it possible to perform layer 2 switching from access networks far into backbone networks (Davik et al., 2004).