27 September 2011
Optoelectronics sustaining innovation in the telecoms market
Even if you have nothing to do with the telecoms industry, it is hard not to see just how rapidly and dramatically things are changing. Just a few years ago, only the most farseeing of commentators could have predicted the revolution we are experiencing; not just in how telecoms networks are used, but also in how they are engineered.
In part, this change has been caused by the inexorable rise of bandwidth hungry services being delivered over the public internet. Applications such as YouTube, Skype and Flickr have gained a common currency and have become a daily source of information and entertainment for wide swaths of consumers in developed economies.
It is becoming increasingly well understood how this telecoms revolution is changing our lives. Today, many consumers would be more likely to download or stream a film than go to their local rental shop, while friendships are increasingly maintained over Facebook and Twitter, rather than via the telephone. This shift has forced telecoms operators to consider some of the broadest changes to the core network infrastructure than have ever been seen before. Networks are having to become faster, more agile and loaded with greater capacity in order to allow operators to keep up with the consumer demand curve and to provide end users with the services they want.
For telecoms engineers, these are exciting times; ones that are opening new ways of thinking about how to construct a network. The industry is currently in a crucial development phase for identifying exactly what the network of the future will look like. In about five years' time, it will become vitally important for a new generation of network to be put in place if the rate of service innovation is to continue to be supported. As module vendors, network equipment vendors and operators all look to what will make up the network of the future, one thing is making itself clear – innovations in the sphere of optoelectronics will be responsible for driving much of this evolution, particularly around the areas of the development of reconfigurable optical add/drop modules (ROADMs, or optical switches) and increases in bandwidth capabilities to 100Gbit/s and beyond.
The long haul mesh networks (highly robust networks used for transporting voice and data traffic over long distances) and Metro Area Networks (MAN) in use today have a relatively limited flexibility in how they can be provisioned and switched. Currently, light channels are established to run in a linear fashion – from point A to point B. If the channels need to be redeployed, engineers need to physically reset the channel so that light is switched to the correct end point. For maximum flexibility to scale their network, however, carriers are envisioning a mesh network in which the end to end optical channels can be provisioned remotely in real time from a control centre, with these optical channels able to carry data traffic at 100Gbit/s and faster. Optical bandwidth can be allocated flexibly to best suit the requirement of the link. This approach is at the heart of what is becoming known as the agile network.
The next generation of ROADMs will play a key role in realising this vision. ROADMs are optical devices that can switch telecoms traffic remotely at the wavelength layer. They have gained currency as a switching mechanism as they remove the need for traffic to be converted from optical signals to electronic signals and back again – speeding the flow of traffic over the network, while allowing for the network to be configured and reconfigured remotely.
Today, colourless-directionless-contentionless (or CDC) ROADM architectures are currently in development to bring about even more flexible networks. In this new architecture, any colour of light can be sent in any direction at any given time without causing interference on the network. This additional network flexibility, combined with improved performance from 40G or 100G transmission rates, would allow carriers to set up or upgrade data paths efficiently within the network, vastly improving bandwidth availability where it is most needed.
The move to CDC ROADMs, and the more flexible networks they enable, is part of a wider trend within the telecoms industry: the need to keep pace with increased network traffic demand. It was only a short time ago that core network speeds of 10G were considered sufficient, but the growth of bandwidth hungry applications has meant that operators have had to quickly look to 40G and 100G to provide the necessary capacity. Indeed, the current belief in the industry is that 100G is a 'sweet spot' and there is evidence that some operators might skip the stepping stone of 40G altogether.
As the industry moves to 100G transmission, something very interesting happens to the optical transmission technique – it becomes coherent. This means that the network is becoming much more sophisticated – instead of light simply being switched on and off to transmit traffic, coherent networks use pure beam lasers to send the data through the network, with phase variations imposed onto the optical beam representing the binary datastream being transmitted. A local oscillator laser is used to extract the 100G data stream by interfering optically with the incoming signal. Electronic processing is then employed to remove noise and reconstruct the 100G data reliably.
There is a high degree of optimism in the telecoms industry around 100G and the general belief is that it will be deployed in the field sooner, rather than later. In fact, we are already seeing the first live deployments of 100G systems and expect the pace to gather rapidly over the short term. Despite this optimism, however, it is clear that the industry should not underestimate the technical challenges that remain around the deployment of both 100G and CDC ROADM architectures. It is vitally important that there continues to be a sustained and significant investment at the module level to guarantee that the right equipment is being provided to network equipment manufacturers and operators alike and companies such as JDSU are already addressing these challenges.
It is an inescapable fact that the services that can be delivered over the internet, as well as across private and corporate networks, will always be constrained by the physics of the technology platforms on which they are founded. The work and investment underway today, around the key areas of 100G coherent technology, as well as the advances in optical switching, means the telecoms industry is well placed to deliver networks that will be able to offer an enhanced range of data rich services that will further transform our lives.
For the end user, this will mean that download times will be improved dramatically, enabling ever richer content and services. It is JDSU's belief that optoelectronics holds the key to the successful delivery of these networks and it anticipates further innovations across this field in the coming years.
Sinclair Vass is JDS Uniphase's senior marketing director for communications and commercial optical products.
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