In recent years optical fibers have become widely used as a communications infrastructure for access networks, also known as Fiber-to-the-x (FTTx), where "x" representing Home (FTTH), Building/Business (FTTB) or Curb/Cabinet (FTTC). According to Quantum-Web's world fixed broadband forecast, by end of 2015 FTTx will count for 20% of all fixed broadband connections.
The rising popularity of optical fibers is contributed to their inherent advantages over the traditional copper twisted pairs, including significantly higher bandwidth capacity, lower power loss, greater reliability and immunity to interference.
Different fiber deployment technologies are used in the access network. Passive Optical Network (PON) is the prevalent one, mainly thanks to its cost-effective architecture and its low energy consumption. PON uses a tree topology, in which the fiber is split once or several times between the service provider's central office or other point of presence and the subscribers' premises.
Gigabit PON (GPON) is currently the most common and fastest growing PON technology. It was in initially standardized in 2004 but went through some major modifications since then. Its throughput is 2.5 Gbit/s downstream and 1.25 Gbit/s upstream and it is capable of supporting up to 128 subscriber end points, commonly called ONUs or ONTs, over a single PON, with distances of up to 20 km.
As new services are being rolled out over PON deployments, the need for higher bandwidth continues to grow. New PON technologies are being developed to address this need. The XG-PON1 technology, also known as NG-PON1, provides 10 Gbit/s downstream and 2.5 Gbit/s upstream and can support up to 256 ONUs/ONTs.
NG-PON2 expands the bandwidth over the PON to 40 Gbit/s in both directions, and this is achieved by two main enhancements: the first, enhancement of XG-PON1 to support 10 Gbit/s in both the downstream and the upstream; the second, stacking of four such systems using different wavelengths on a single PON, so that their aggregate data rate is 40 Gbit/s symmetrical. This technology is also referred to as Time and Wavelength Division Multiplexing (TWDM).
NG-PON2 is still in the standardization process, but some vendors have already announced supporting products to be launched during 2015, followed by a significant number of service providers in many countries that are planning NG-PON2 deployments within the next few years.