ORLANDO--With major carriers such as Verizon Communications deploying gigabit passive optical networking (GPON) gear for fiber-to-the-home (FTTH), Alcatel-Lucent today described some likely successors to GPON at the FTTH Conference today.

There are three likely candidates for GPON’s successor, according to Ronald Heron, Alcatel-Lucent’s director of network portfolio strategy and chief access technology officer: a next-generation version of GPON still based on time-division multiplexing (TDM), much higher speed wavelength-division multiplexing (WDM) PON, and a hybrid of those two approaches. Of these, Heron saw the hybrid approach as the leading candidate based on a number of factors.

While hybrid systems might emerge sometime in the next three years—even next year, possibly, Heron said, pure WDM PON is “not economical in the foreseeable future.”

In a next-generation GPON network, new wavelengths would be deployed on top of old ones, substituting 10 Gb/s for 2.5 Gb/s links. That would require carriers to replace the filters in their customer’s premises gear, which would be no small task. And it would require a 6 db or 7 db increase in the optical budget to deal with the four-fold increase in bandwidth. Some manufacturers have investigated an integrated approach to this concept, Heron said, using a single transmitter and a single downstream wavelength that operates at two different modulations to offer the new, higher speed.

In a hybrid system, carriers would replace their GPON wavelengths with four different GPON wavelengths, all within the existing 20 nanometer window but partitioned in smaller 5-nm slices. Carriers might add filters to the nodes between their central offices and their customers rather than to all customers’ homes. The customer premises gear need not necessarily be changed in that scenario, Heron said. “They’ll see whatever light’s coming their way.”

WDM PON would provide the most bandwidth to users but is also the least efficient, since bandwidth is not shared among subscribers. It also poses some technical challenges, Heron said, such as the difficulty in assigning wavelengths at the customer premises gear, solutions for which can be complex and expensive. WDM PON providers may opt to use wavelength-selectable splitters, he said. “You’d just set it and forget it.”

Today’s GPON technology should be able to meet consumer demand through at least 2011, Heron said, especially since the bandwidth to each user can be increased by reducing the number of times the fiber is split among users.