Photonics can relieve radio congestion in space telecommunications
Space market research firm Euroconsult estimates that some 26,100 small satellites will be launched over the next decade—almost four times more than in the previous decade. Most of these will be part of broadband mega-constellations in lower-Earth orbit, such as Elon Musk’s Starlink or the UK’s OneWeb. Unavoidably, as the number of satellites in space increases, fresh problems will appear, and existing risks will grow. For example, satellites will be at increasing risk of collision, and space debris will be increasingly likely to fall from the sky. The radio frequency spectrum will become ever-more crowded.
The European Space Agency’s (ESA) Space Safety Programme (formerly the Space Situation Awareness programme) does a great job of monitoring hazards from space, assessing the danger, and making this data available to the appropriate authorities so that, where possible, threats such as colliding satellites can be mitigated. But radio congestion—admittedly less dramatic than crashing satellites—remains a problem without a clearly defined solution.
And it is a problem. Radio interference can degrade the quality of communication, causing data loss, failed calls, and service disruptions. Given that satellites perform critical functions, such as Earth observation for weather forecasting and GPS services, interference is more than highly inconvenient. It is dangerous. Dropped calls, slow internet connections, and interrupted broadcast services, for instance, could have a huge impact on disaster response and emergency services, which increasingly depend on satellites. If radio were to be disrupted, emergency services units may not be able to coordinate responses, and the results would be catastrophic.
And there are commercial reasons to be concerned about increasing radio congestion. Telecommunications, for example, might experience considerable disruption, affecting the ability of individual companies to communicate reliably and conduct business in a timely way. In the financial sector, for example, timeliness is crucial.
Enter photonics—specifically, optical communication. Thanks to the narrow shape of a laser beam, optical communication, unlike radio, isn’t prone to interference from other signals. It doesn’t spread or leak. In fact, it’s almost impossible for laser interference to happen. What’s more, laser signals aree very hard to intercept. Technically speaking, this feature is classified as low probability of detection and low probability of intercept. It is particularly helpful in military and strategic communications where jamming and eavesdropping are concerns with potentially lethal implications.
Furthermore, the rate of data transmission via laser is far higher than for radio—up to 100 times faster. It means that vast amounts of data could be sent back and forth easily, and that the available spectrum would be used more efficiently. Because the optical spectrum has a wider bandwidth compared to radio, congestion, which isn’t likely now, also wouldn’t be likely even as the growing demand for space-to-ground communication channels is being met.
But if laser has these advantages, why isn’t it used more often? The fact is that since the earliest days of laser development, researchers have understood that, due to basic physics, it could outperform radio in terms of speed and density. Lasers have been used for years: reading CDs and DVDs, for instance, or scanning barcodes in supermarkets. The reason they have not supplanted radio is because point-to-point laser communication over vast distances, through air or space, has been limited by atmospheric turbulence. Differences in temperature, wind, pressure, and the composition of gases in the atmosphere could degrade the quality of a laser link. At Cailabs, we have developed a technique called multi-plane light conversion (MPLC) that solves this problem. MPLC involves beam shaping, based on iterative modifications of the beam’s transverse profile after successive reflections onto a phase plate. It preserves the resilience of the laser link even as it passes through the atmosphere. It means that laser can be used instead of radio, thus tackling the thorny issue of radio congestion.
So, should laser replace radio entirely? No. Radio has shown itself over time to be a highly reliable technology for a wide variety of purposes. But with the proliferation of wireless devices and services, such as smartphones, WiFi networks, satellite communications, and broadcasting services, the demand for access to the radio spectrum has significantly increased. Laser, meanwhile, has come of age, and as a mature technology with clear advantages and a diverse range of applications, it, too, has a role to play in communications. A hybrid approach to space communications that involves the use of both radio and laser would be advisable. It would allow us to make use of the unique characteristics of both technologies while avoiding their pitfalls.
We are becoming increasingly dependent on satellites for security, connectivity, and for dealing with global challenges such as climate change. Recently, MethaneSat, a Google-backed small satellite, was launched with the aim of tracking greenhouse gases.
Given our reliance on satellites, and how the new space race between the US, China, and other countries is intensifying, it’s paramount that we confront and deal with problems like radio congestion before a potentially costly or dangerous incident forces the matter. We need to anticipate technology problems in space communications and meet them ahead of time.
Jean-François Morizur is CEO and co-founder of Cailabs (www.cailabs.com/).
