Continued… DWDM Part IX


Passive optical networks (PONs) have evolved to provide much higher bandwidth in the access network. A PON is a point-to-multipoint optical network, where an optical line terminal (OLT) at the CO is connected to many optical network units (ONUs) at remote nodes through one or multiple 1:N optical splitters. The network between the OLT and the ONU is passive, i.e., it does not require any power supply.

PONs use a single wavelength in each of the two directions—downstream (CO to end users) and upstream (end users to CO)—and the wavelengths are multiplexed on the same fiber through coarse WDM (CWDM). For example, the Ethernet PON (EPON) uses 1490 nm wavelength for downstream traffic and the 1310 nm wavelength for upstream traffic. Thus, the bandwidth available in a single wavelength is shared amongst all end users. Such a solution was envisaged primarily to keep the cost of the access network low and economically feasible for subscribers. Various blends of the PON have emerged such as the Ethernet PON (EPON) of IEEE 802.3ah [1], the broadband PON (BPON) of ITU-T G.983, and the generic framing procedure based PON (GFP PON) of ITU-T G.984.

An enhancement of the PON supports an additional downstream wavelength, which may be used to carry video and CATV services separately. Many telecom operators are considering to deploy PONs using a ?ber-to-the-x (FTTx) model (where x = building (B), curb (C), home (H), premises (P), etc.) to support converged Internet protocol (IP) video, voice, and data services—de?ned as “triple play”—at a cheaper subscription cost than the cumulative of the above services deployed separately.

Although the PON provides higher bandwidth than traditional copper-based access networks, there exists the need for further increasing the bandwidth of the PON by employing wavelength-division multiplexing (WDM) so that multiple wavelengths may be supported in either or both upstream and downstream directions. Such a PON is known as a WDM-PON.

Interestingly, architectures for WDM-PONs have been proposed as early as the mid-1990s. However, these ideas have not been commercialized yet for many reasons:- lack of an available market requiring high bandwidth, immature device technologies, and a lack of suitable network protocols and software to support the architecture. It is believed that many of the above factors have been mitigated over the years.

Below is the abstract of Frost & Sullivan Market Insight on “WDM PON: How Long Is It Going To Take?”, which was authored by Adeel Najam and published on 16 Nov 2009 ~

Although wavelength multiplexing seems like the ideal path for PON technology evolution with advantages like scalability and capacity boost, WDM PON technology needs to mature before it can become widespread. Shooting multiple waves in a fiber is the logical way to maximize the utilization of fiber and maximize the investment in the network. The idea is right with WDM-PON but the technology still needs 4-5 years to become practical.  …….

However WDM-PON has significant potential when the third wave of fiber deployments comes in 4 to 5 years. The third wave of fiber deployments will be the largest one and will come when fiber local loops are deployed in the urban areas of emerging markets. With the growth in wireless broadband, wireless providers will also start to connect their bay-stations with fiber. By that time WDM PON is expected to have matured to be used as an attractive PON technology.”


Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access by Amitabha Banerjee and others, Optical Society of America.

WDM PON: How Long Is It Going To Take? by Adeel Najam, Frost & Sullivan Market Insight

To be continued… DWDM Part XI