Innovation: Let there be light

Charles Kao.jpg

All-optical networks that use photonics are the industry’s dream solution to the ever-increasing demand for speed. Alan Burkitt-Gray talks to Fabienne Saliou, a research engineer at Orange, which is running an exciting project using this tech

In 1966, two scientists, Charles Kao (pictured) and George Hockham, released a research paper that showed it was possible to transmit data in the form of light along glass fibres. Their early demonstrations, more than half a century ago, were held in what was, at the time, one of the world-leading research centres for the industry: Standard Telecommunication Laboratories (STL), in Harlow, just north of London.

Their supervisor, Alec Reeves, also invented pulse-code modulation, the first method of digitising voice for telecoms.

Kao and Hockham were lucky in that lasers and photodiodes had recently been invented, and these formed a useful way of turning digital electrical signals into pulses of light, and light back into electric pulses at the other end.

And that has defined the architecture of optical fibres ever since. Digital electronics to digital light to digital electronics and then back again for the next leg of the journey.

If you have fibre-to-the-home (FTTH), for example, the signal runs along optical fibre to the termination point on the wall of your home; after that it’s back to using copper wires. (In my case, sadly, fibre stops 200 metres down the road, and then it’s back to 30-year-old copper wires.)


Light all the way

Even since, scientists and engineers have been dreaming of the day when you don’t need that electrical interface between two stretches of fibre: end-to-end light is the idea. So, it was a dramatic moment at the end of 2022 when Orange disclosed its role in the heart of a research and development project to develop new networks that use light all the way.

The term for this technology is “photonics”. It’s a word that’s been around since the late 1960s, not long after Kao and Hockham completed their pioneering work at STL. It’s clearly been a dream of telecoms engineers that, one day, they should be able to send signals as continuous light from source to recipient.

Orange’s project, called Octapus, aims to establish photonics as a key enabler in next generation networks. (‘Octapus’ is not a typo: it’s a highly contrived acronym that Orange says stands for “optical circuit switched time sensitive network architecture for high-speed passive optical networks and next generation ultra-dynamic and reconfigurable central office environments”. No, I don’t see it either.)

Orange is working with a number of other telecoms companies and several European universities – including the University of Southampton. This is good, because the project is being funded by the European Union’s Horizon Europe programme and the UK’s departure from the EU three years ago usually means the country’s academics are unable to access EU funding for their projects.

To get a better idea of how photonics might transform telecoms I talked to Fabienne Saliou, a research engineer at Orange’s labs in Lannion, Brittany, who is working on the use of photonics in access networks. (In other words, to replace that nasty bit of copper Openreach uses to connect me to fibre in London.)

“The equipment at the node hasn’t changed for 15 years,” she tells me. It’s very early days. Saliou and her colleagues started their work in September 2022. “We’re preparing the specification for use cases and we’re starting to design the photonics – the emitters and the receivers.”


Compound semiconductors

One of the research streams is looking at using semiconductors – either silicon, which has been used for decades for silicon chips, or compound semiconductors that are made of so-called III-V materials. There’s also work on lasers to do, and more to integrate everything into a system.

“The project will last until 2026,” says Saliou, who has a doctorate in optical and electronic communications from Télécom Paris, one of France’s outstanding grandes écoles (“big schools”, a term which doesn’t quite convey their importance as France’s leading specialist universities).

The expectation is that Orange’s work will be the first in a programme of advanced work that will lead to devices that can enable optical networks working at 50Gbps. That means delivering 50 gigs into the home, about 1,000 times what I get today.

Once photonic devices emerge from their labs and field trials, Saliou says there will be several developments. “We will be able to reduce latency” without the need to transition into electronics, “and it will be possible to have a photonic bypass”, which she defines as a switch that enables direct connection to a content server.

Orange is part of the Innovative Optical and Wireless Network (IOWN), which includes some of the world’s leading telecoms technology companies. Intel, NTT and Sony founded IOWN, and it has around 30 sponsor members, including Orange and SK Telecom. Its first meeting will be held in March 2023.

“We’re all talking,” says Saliou. Once the requirements for photonics are specified, IOWN’s work will move onto bring photonics out of the laboratory.

Clearly, the future is bright. Not just with Orange light, but with all colours of light. ‘Fiat lux,’ as someone once said, several thousand years ago.