Photonics Provides a Working Sidestep Around Radio Congestion

JEAN-FRANÇOIS MORIZUR, CAILABS

The number of satellites orbiting Earth is increasing so rapidly that the European Space Agency has dubbed 2024 a “year of launches.” According to the satellite tracking website Orbiting Now, more than 10,100 active satellites are orbiting Earth. Some are equipped to take pictures of our planet, and some capture images of other celestial objects. Some monitor the weather, while certain satellites continue to transmit data, provide internet access, and connect phones.

In each case, losing access to these satellites would disrupt our way of living.

But as the number of satellites rises, so does the demand for connectivity. This in turn pushes the limits of the radio spectrum. Rapidly, radio congestion is becoming a serious issue and is already raising concern.

As a rising number of satellites brings the world closer to critical levels of radio congestion, lasers could offer a solution to crowded skies. Courtesy of Cailabs.

Broadly speaking, there is a limit to how much data can be sent in a given volume of space, at a given time, in a given portion of the spectrum. In some form, we have all experienced these phenomena. When mobile phones are used in a large group and in the same space, we are apt to face patchy signals and low throughputs.

A photonics-based system serves to not only free up room but also ensure our ability to achieve communications that sidestep the congestion problem altogether.

Similarly, satellites that are attempting to communicate when there are many other satellites in close proximity are subject to interference and poor communication quality. They will need to use different parts of the spectrum to avoid encountering these conditions. However, this presents a challenge: There is not much of this spectrum to go around. Further, the radio spectrum is already a shared space, because it enables, among other things, our phone communication, emergency services, TV, and, of course, satellite communication.

Fortunately, photonics offers a solution to this shortage of spectrum. A photonics-based system serves to not only free up room but also ensure our ability to achieve communications that sidestep the congestion problem altogether.

Shannon’s law and the power problem

There is no practical way to outright circumvent radio congestion. According to Shannon’s law, every communication channel has a finite capacity for transmitting information. More precisely, it becomes exponentially harder to transmit more bits per second, since it requires exponentially more power to do so. Because there are power limits in any system, such as solar power limits on satellites, there is a fundamental limit to how much data can be sent per unit of time. If more people want to communicate, they must share the same capacity, typically using the same channel in succession. This is called time division multiplexing.

The concern that arises calls into question how close we might be to problematic levels of radio congestion. While we do not know with absolute certainty, we do know that the number of satellites in orbit is rising, and countries are already limiting the right to use certain parts of the radio spectrum because they fear that radio congestion is inevitable and will soon restrict their ability to communicate.

Even if some find such fears to be unfounded, they have an effect, nonetheless. A solution would ease these fears and provide a viable alternative for the efficient transfer of data.

How photonics can help

Unlike radio waves, which disperse and are susceptible to interference because they occupy the same information channel, laser light propagates along a narrow, focused beam, making interference unlikely. Every laser beam is a spatially independent channel. And, given that laser light is very high frequency compared to a radio wave, it can carry much more data. A single strand of optical fiber, for example, carries ~50 Tbps of data — the world records are in petabits per second — while achieving ~15 Gbps for a radio satellite link.

As a result, optical communication options are simply not subject to congestion.

And the advantages extend beyond improved speed and efficiency. Lasers produce light that is highly directional, as well as coherent. Parallel light waves maintain both their phase and amplitude over longer distances, compared with radio waves. Since lasers concentrate their energy in a specific direction, they reduce energy dispersal and also allow the light to travel long distances with minimal losses to power.

Radio waves, on the other hand, spread out more than light waves, which leads to significant power spread over distance. This is particularly important for space exploration, where distances are given in astronomical units and not in kilometers, and it is already an obstacle to create a viable moon network, since the moon is ~384,400 km (0.00257 AU) from Earth.

All constituents must recognize the urgent need for more efficient, secure, and scalable communication technology as humanity’s footprint in space expands amid tomorrow’s communication demands.

In optical transmission systems, the relationship between data throughput and power consumption depends significantly on the system architecture — and the relationship is, in fact, a bit nuanced. While increasing data throughput typically requires more power in electronic systems, photonic systems modulate data onto the laser beam without a proportional increase in power consumption. The primary energy expenditure in these systems is maintaining the laser beam’s integrity and direction over long distances. Once the beam is stable and capable of reaching its target with minimal loss, data throughput can be enhanced by adjusting the modulation techniques — in other words, the method by which data is encoded onto the light. However, the exact effect on power consumption may vary based on the specific architecture and technologies used in the transmission system.

Safe communication in an unsafe world

Security benefits are another perk of the use of lasers, and these benefits have been highly relevant in recent years. According to the Armed Conflict Location and Event Data (ACLED) project, global conflict rates increased 12% in 2023, with >15,000 more attacks, bombings, and assaults compared with 2022, which experienced a 32% increase from 2021. The ACLED says one in six global citizens now live in an area of active conflict; defense budgets are increasing around the world.

Laser communication is difficult to detect and highly resilient to interception and jamming. These benefits illuminate the distinct advantages of laser communication in war zones, where reliable and timely communication is essential to coordinating military strategies, typically conducted in secret.

A paradigm shift

Even with the benefits of laser communication, challenges must be overcome before the number of lasers can be increased in satellite communication, thereby triggering a paradigm shift in this realm of communications. One seemingly intractable historic challenge pertains to atmospheric turbulence, which degrades laser beams in much the same way as frosted glass warps light, for example. Companies, including Cailabs, have developed techniques and technology that overcome the problem. Cailabs’ solution involves beam reconstruction, among other, varying approaches.

A present issue is that lasers for large-volume communications have not been tested at the necessary industrial scale. For this reason, many view the technology alternative as unproven and prefer to stick with the legacy radio technology. Though often mindful of the need for new forms of communication, skeptics fear investing in what they consider experimental technology.

Instead, it is up to those of us in photonics to demonstrate the field’s reliability and cost-effectiveness of laser communications in practical, real-world contexts.

Advancing this technology also demands changes to the regulatory and economic environments. The current system for managing radio frequencies is mired in complex legal and bureaucratic procedures, which are both expensive and time-consuming. Photonics can simplify communication efforts but will require a concerted response from industry leaders, regulators, and policymakers. All constituents must recognize the urgent need for more efficient, secure, and scalable communication technology as humanity’s footprint in space expands amid tomorrow’s communication demands.

At the same time, this is not a call to replace radio, which is time-honored and still delivers irrefutable benefits. Photonics can instead supply a helping hand. The skies are only going to become more crowded, with both private and public players launching satellites with enthusiasm and demands for faster and more reliable connectivity increasing at a rapid pace.

Photonics promises higher data rates, lower power consumption, excellent security, and outstanding reliability. In respect to creating a safe, globally connected world, it is an important piece of the puzzle.