To deliver high-speed internet to our households, telecommunication operators have different technologies to choose from. The most advanced technology is based on optical fibre cables and is therefore called fibre-to-the-home (FTTH). The FTTH variant more commonly used in Europe to provide FTTH services is Gigabit Passive Optical Network, or GPON. Here’s how GPON works.
The evolution of the world-wide web (or internet): Faster, better, stronger
Since the mid-1990s, the internet has revolutionised our lives and there is an ever-increasing demand for faster and more reliable data traffic. High definition or even 4K video streaming, teleworking, videoconferencing, etc., are some of the commonly used internet-based services driving the explosion of data and bandwidth. The confinement and lockdown period during the Covid-19 crisis has shown the importance of good, reliable internet connectivity at home. A high-speed connection at home has opened up the possibility of efficient teleworking, maintaining entertainment habits and keeping close contacts with our loved ones through videoconferencing. Data traffic in all networks has increased significantly during the confinement period.
The first telecommunication networks were built using copper cables as the physical medium to transmit the signal. For many years, these networks would be used for basic telephony services, mainly voice and telegrams. With the expansion of the internet since the mid-1990s, voice has been progressively replaced by data. And this quickly showed the limits of copper in transmitting data, so optical fibre technology was developed as a response to this constraint.
But first, why is fibre-optic technology capable of providing faster and higher-bandwidth services than copper technology? Copper transmits electrons, while glass fibre transmits photons. In other words, the fibre cable transmits light, which travels faster than electrons, providing higher speeds. And, when sent over an optical cable, optical signals diminish less over distance than electrical signals over copper cables.
The first optical networks were rolled-out at the end of the 1980s. Initially, they would be used for submarine or long-distance fibre cables that connected big cities, like New York with London or London with Paris, for example. Progressively, the entire internet backbone came to run on fibre-optic cables that replaced copper cables.
And once the backbones increased their capacity thanks to the optical fibre, the technology was spread out gradually, first connecting large business and public administration buildings, and eventually covering individual households.
GPON is a river of light
Here’s how GPON networks are designed:
The main optical transmitter, called the OLT (Optical Line Terminal) is located within the telecommunications operator building, the central office. A laser in the OLT injects the photons from the central office to a fibre-optic cable made of glass and plastic that ends at a passive optical splitter. The splitter breaks the single signal from the central office into numerous signals that may eventually be distributed to up to 64 customers. The number of customers served by one laser is a result of the operator’s engineering criteria, which might choose to lower the number, very often to 32 customers.
Furthermore, the operator might decide to split the signal twice, for example once into eight and further down the cable again into four. The maximum distance between the central office can be 20km, although operators will usually limit it to 16km, to be able to provide a good quality of service.
Andres Gavira Etzel, lead engineer at the European Investment Bank, explains that the advantage of optical fibre is that its signal attenuation—the reduction in the signal’s strength over long distances—is much lower than in an electrical system.
“Imagine both technologies as a river that goes through a small town,” Gavira Etzel says. “For the copper, the channel gets smaller and smaller, so it is more difficult for the electrons to go through. In the optical system, the channel is always the same, so they go through more or less till the end. In addition, the signal from one copper cable will alter the signal of an adjacent cable, degrading the signal even further.”
Within the 16km range of a fibre central office, then, all households can have high-speed internet, in contrast to ADSL technology, whose signal deteriorates as the distance between the central office and the household grows, with already significant loss of signal after 3km.
The quality of fibre service is at least 10 times better, from up to 100 megabits with a copper-based network to one gigabit with fibre, although it will usually be even higher as a copper-based system will not reach above 50 megabits.
Optical fibre is a more energy-efficient, future-proof technology
But the lower attenuation and the possibility of splitting one fibre into many also has advantages over the copper technology from an energy efficiency point of view. Due to the higher attenuation, operators must inject more power into a copper line from the central office than to a fibre equivalent. For copper ADSL, operators calculate about 1.8 Watt per user. Recent analysis shows that fibre reduces this energy to 0.5 Watt per user. Multiplying this by millions of users in Europe shows the potential CO2 savings we can achieve when migrating to fibre.
As a relatively recent technology, fibre-optic cables are yet to be fully deployed throughout Europe. But as in any telecommunication technology, equipment manufacturers are already working on the next technology with even higher speeds. Fibre networks have the potential to upgrade to its next generation by changing the laser without changing the costly fibre roll-outs.
“This is a future-proof technology with higher capabilities and increased energy efficiency,” says Gavira Etzel.
That’s why the European Investment Bank is participating in the national efforts to make quick and reliable internet accessible to everyone, by financing a number of projects related to optical fibre infrastructure roll-out. The EU bank’s fibre-optic projects can be with operators directly or as part of government schemes, mainly in Europe but also outside.