Events in Brussels provide WDM–PON insights

Nov 1st, 2008

by Gerlas van den Hoven

For two weeks in September, Brussels, the political capital of Europe, also became the fibre–to–the–home (FTTH) capital. The city first hosted the European Conference on Optical Communications (ECOC), which was directly followed by the Broadband World Forum Europe (BBWF), both conferences held in the shadow of Brussel's beautifully restored Atomium building.

The combination of the two conferences provided insights into the technical and commercial market situation for FTTH in Europe. First, FTTH is here to stay. Access networks are now a dominant part of the technical program of ECOC, while the equipment vendors at the BBWF displayed a whole range of new products targeting FTTH. Not surprisingly both conferences raised the key question on network architecture, "Which network fits best for Europe, point–to–point or passive optical networks (PONs)?"

The question wasn't really new. But the really interesting thing is that the industry is starting to formulate an answer. And that answer isâ�¦ neither, and yet both at the same time. This may sound cryptic, but the answer is quite obvious: The long–term solution for access networks is likely to be WDM–PON.

In WDM–PON, as its name implies, multiple wavelengths are used to provide bandwidth to each user in the network. In fact, each user is given its own wavelength, thereby getting around the issue in a normal PON where the users share a communication channel. At the same time, all the wavelengths are provided over a common fibre and are separated close to the end–users. This gets around the shortcoming of normal point–to–point networks where each user requires a separate fibre. Viewed from the networking perspective, WDM–PON is logically point–to–point, while physically a PON. The best of both worlds, one could say!

As an equipment vendor, my company believes in WDM–PON in the long term. But before we and others dive into the development lab to design a product, a word of warning is in order. While some vendors have "introduced" WDM–PON to the market, the essential technology is far from mature.

According to some industry experts at ECOC, the WDM splitter is the most important component for WDM–PON. At Genexis, we disagree. While the WDM splitter is indeed in the centre of the network, the most important components are found at the ends.

The user side requires a colourless transceiver. It needs to be able to send and receive optical data packets regardless of the wavelength it has been assigned. At the central office, the challenge is even greater; each user requires its own wavelength and hence its own transceiver. All of these wavelength channels must be combined, and furthermore, a second set of wavelengths must be generated to provide each user with a locking signal so it knows which wavelength channel to use for the upstream communication.

Besides being costly, these systems are also still quite bulky and certainly very power inefficient. A last issue is WDM–PON's lack of standardisation.

On the bright side, WDM–based FTTH systems do solve the fundamental problems of current optical access networks. Many companies, including Genexis, are actively developing technology that will create a breakthrough for WDM–PON in a few years.

One example is the development of the reflective semiconductor optical amplifier (RSOA), which is the enabling component for the colourless transceiver. At its ECOC–stand, UK–based component manufacturer CIP showed great progress with its un–cooled RSOA component that can easily support 1 Gbit/sec. This technology can go much further as CIP showed in the technical sessions with a 10–Gbit/sec demonstration. However, practical devices such as the un–cooled RSOA are more important for the success of WDM–PON as a realistic access network technology.

Even though WDM–PON will take some years to reach maturity, we can already make some important conclusions about this industry trend.

WDM–PON can be operated with pure and simple Ethernet, and just like point–to–point Ethernet systems, it provides symmetrical bandwidth that is scalable per user. The fact that both PON adepts and point–to–point fans embrace WDM–PON shows that these factors are of key importance to fibre access networks. The technology also fits well within the European trend to deploy Ethernet–based systems that are open to multiple service providers, in line with the thoughts from EU regulatory bodies.

Coming back to the present, we see that FTTH is broadly acknowledged to be the growth market for the next decade. The FTTH technology space is teeming with development efforts, and these efforts are all starting to converge towards a common ground.

For the near–term however, the new world financial situation will certainly have an impact, although we firmly believe that broadband communication is no longer something nice to have, but is rather a necessity in today's society and in everyone's day–to–day life. People want to communicate and they want to do so in the most open and easy way, without limitations.

Therefore 2009 should be another year of strong growth, in spite of the global financial situation. With more than 100 projects deploying FTTH, the demand for simple–to–install, easy–to–use, and energy–efficient products for FTTH will increase and help create healthy business cases for optical access networks.

Gerlas van den Hoven is CEO of Genexis (

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