Paul van Gerven
15 April

By developing free-space optical communication technology and deploying it on Earth as well as in space, a recently formed Dutch consortium is going to give RF communication – and the optical fiber, for that matter – a run for its money.

Wi-Fi and other wireless communications techniques are great, but they have their limits: there’s only so much data you can squeeze into the radiofrequency spectrum. Even with advanced signal modulation and spatial multiplexing techniques, it’s a struggle to keep up with the exponentially growing data demand. Tellingly, 5G has to annex another part of the electromagnetic spectrum – the millimeter-wave domain – to open up additional capacity.

Further up the spectrum, in the visible and infrared region, there’s even more bandwidth available. We’re quite familiar with that part, of course, because packets of light have been zipping through optical fibers for decades already, at high speed and with low latency and excellent energy efficiency. Efforts to release these photons from their glass prisons have been started years ago, but there’s still some way to go before radio waves get serious competition from optical wireless communication.

A Dutch public-private partnership consisting of five universities, two research institutes and fourteen companies (see inset) have set out to push things forward. Having been awarded 4.1 million euros by science financier NWO, the Free consortium is aiming to develop free-space optical communication at all length scales. In other words, whether it’s for connecting your laptop at home or for inter-satellite communication, the collaboration wants to build a wireless optical link for it.

Apart from providing high bandwidth, free-space optical communication (FSO) has a number of intrinsic advantages, says Free program leader Eberhard Gill, professor of Space Systems Engineering at Delft University of Technology as well as scientific director of the TU Delft Space Institute. “FSO links are directional, so, unlike radio waves, they don’t spread out. This has two important consequences: they’re inherently more energy-efficient. Additionally, there’s no need for spectrum licenses. On top of that, FSO could be the most practical way to obtain the ultimate data security: quantum encryption.”

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The ambitions of the partners go beyond developing the FSO links over various distances, however. They envision using them to set up the ultimate ‘network of networks,’ in which a globe-spanning network of (mini)satellites is seamlessly integrated with ground-based networks. The ability to route connections through space opens up new opportunities for a wide range of applications, particularly those involving moving objects in need of high-bandwidth, low-latency connections. “From a network point of view, it would no longer be relevant whether a node is a drone, a satellite or a car,” says Gill.

free space optical links
Credit: TU Delft

Practical

Unsurprisingly, the space networking aspect of the project enthuses space engineer Gill in particular. “By linking the space and terrestrial domain, we’re moving away from the idea that these domains are separate. Space research and technology is often seen as a field of its own, having little overlap with the equivalent terrestrial applications. I’m really excited that we’re going to bring them together.”

But in case of the Free program, it also makes a lot of sense to bring them together, Gill explains, as there are many commonalities between optical wireless communication technologies for space and terrestrial settings. “Receivers are a good example. We’ll be looking at developing receivers that are much more efficient than they currently are. It goes without saying that these devices will be equally useful for space and terrestrial applications.”

small satellite network
Credit: TU Delft

“Developing actual applications will be up to the participating knowledge institutes and companies, of course, but the goal of the program is to push the technology readiness levels considerably. We want industry to be able to pick this up as early as possible, and we’ve taken a lot of steps to make sure the technology we develop will be manufacturable and practical in the real world.”

“So, for example, all research questions of the fifteen PhD students that will work on this project will be verified and approved by industry. We’ve defined sixteen use cases, which dictate the requirements for all technologies to be developed. And to smooth the transition from research to industry, we have an Architecture and Integration work package to spot manufacturability and system integration issues at an early stage.”

Competitive advantage

The big question, then, is when the world will start building the optical wireless superhighways that the Free consortium is envisaging. “That’s really hard to tell. All I can say is that I expect FSO technology to be adopted gradually. Initially, it might be in niche applications such as beaming down data from earth observation satellites. As the technology develops and matures, it will enter into more and more mainstream applications. Eventually, it will compete with RF in a lot of applications, though I don’t expect FSO to make RF obsolete entirely.”

“It won’t take fifty years to reach that stage, nor will it take five. Let’s just say that I expect to see quite a move in FSO within the next ten years. After all, there’s a need for it in our increasingly digital society – the demand for bandwidth keeps growing. It will be a big market and I’m convinced our consortium will give the Dutch industry a significant competitive advantage.”