WDM?s Bright Future for FTTx Deployments

Wavelength Division Multiplexing (WDM) is accelerating in importance as an essential ingredient technology for fiber optic communications.

It’s well-known that passive optical networks have become the dominant technology for FTTx deployments due to significant advantages over active networks in terms of initial and ongoing cost structure. Existing PON access network standards use WDM to support bidirectional traffic over a single fiber using three wavelengths. For example, the G.984 G-PON standard defines 1490 nm for downstream digital traffic, 1550 nm for downstream RF video overlay and 1310 nm for upstream digital traffic.

The International Telecommunication Union (ITU) has extended the G-PON standard with the NG-PON2 initiative (sometimes referred to as WDM-PON), which defines new fiber spectrum at 1596 to 1603 nm (downstream) and 1524 to 1544 nm (upstream) that explicitly coexists with legacy G-PON (and 10G-PON) wavelength allocations. WDM-PON leverages the ITU CWDM and DWDM standards originally developed for core networks, and allows the establishment of logical point-to-point connections over a point-to-multipoint physical network topologies.

Critically, the 4 wavelength x 10 Gbps downstream WDM-PON approach preserves existing service provider optical distribution network investments, with only OLT and ONT equipment upgrades required. WDM-PON allows carriers to segregate traffic using different wavelengths, enhancing end-to-end security. Furthermore, WDM-PON prescribes the use of time division multiplexing (in addition to wavelength division multiplexing) for both the forward path and the reverse path to optimize network infrastructure resource utilization. This TWDM option supports up to 1:128 splits per wavelength, and uses established G.694.1 dense channel grid spacings. A point-to-point per wavelength option lends service providers with a choice of shared and expanded spectral regions, with both adhering to G.694.1 dense grid spacings. The WDM-PON expanded spectrum (which extends from 1524 to 1625 nm) is targeted to greenfield deployments where the reuse of OLT and ONT equipment and legacy wavelength coexistence are not concerns.

This combination of methods gives service providers the capability to meet the most demanding transport applications such as public cloud access for large enterprises and next generation 5G mobile fronthaul. NG-PON2/WDM-PON lays out a roadmap for service providers to cost-effectively reach bandwidth levels forecast for 2020 and beyond while preserving much of their existing PON network infrastructure investment. It seems the remarkable scalability of fiber data communications will continue into the foreseeable future.

AFL’s WDM900 Lightwave Test Set is designed to ensure increasingly vital WDM-based equipment and fiber network assets remain healthy and continuously productive. If you have any questions, please feel free to contact AFL.