Laser communications are a secure and robust new option for communicating massive amounts of data both between satellites in the air and between satellites and the ground. But lasers also have their shortcomings, including the complicated problem of controlling the shape of light and limited geographic options for ground stations. Constellations spoke with Jean-Francois Morizur, Founder and CEO of Cailabs, about the market for laser communications and how they complement RF signals in satellite connectivity.

The Optical Telescope

Laser communications “work in the optical spectrum, or in wavelength,” said Morizur. They carry data from satellite to satellite or from satellite to the ground, in much greater quantities than usually possible with traditional methods like RF. “It’s a very narrow beam of light,” said Morizur. “Once you are within that link, you can carry far more data.”

Ground stations for laser communications include an optical telescope rather than the RF antenna that most are familiar with—the large dishes often seen on the roofs of buildings. The optical telescope tracks a satellite and points to it with a very fine accuracy. “You’ve got a first course tracking, and then you’ve got a fine tracking, where you’re using active laser from the other side to know exactly where to point,” said Morizur. The rest of the ground system, including the data processing and the modem, are very similar to existing RF ground stations. “Basically, it’s like changing the top of something, but then the rest of the infrastructure remains very similar,” he said.

Some of the greatest challenges of working with lasers—especially for those who have long been working with RF—are maintaining pointing accuracy and dealing with natural interference. Laser is much more difficult to point accurately, as the ground area is usually tens of meters, rather than the tens of kilometers available when using RF.

A Unique Geographic Challenge

Radio interference isn’t a problem for laser, but natural atmospheric interference is a massive one. “The challenge is going to be weather,” said Morizur. “So your clouds, coverage, and also the turbulence that comes with going through the atmosphere.” Morizur emphasized that satellite operators interested in optical need to understand these challenges when adding optical telescopes to their networks.

“Usually in RF, you had polar ground stations, [which] are very close to poles, because then they could connect to satellites and orbits,” said Morizur. The problem? “There would be very high cloud coverage,” which creates a problem for optical telescopes, which call for geography with minimal atmospheric interference. Geographical placement for optical ground stations also prioritize access to fiber optics, said Morizur, “because you have so much more data now [and] you need to carry that into your network efficiently.”

Many satellite operators instinctively want to place their optical telescopes next to their existing RF ground stations. But placing them together can create more problems than solutions. “When [the light] goes from the satellite to the ground, it is deformed by turbulence in the atmosphere,” causing the beam of light to warp and lose the ability to carry information. “This is really a question of beam shape. They call it an echo… this is what kills the beam, or the ability of the beam to carry information,” said Morizur. When ground stations are placed well, optical ground companies like Cailabs can preserve the shape of light as it moves from satellite to the ground—a necessity in getting data to the ground accurately.

High Security Comms

Optical laser communications are inherently highly secure. “If you’ve got two laser beams, two laser pointers, there’s not going to be influence from one laser to another,” said Morizur. “You are looking at point to point links that will not crosstalk, that will not contaminate each other.”

Lasers are qualified as low probability of detection, low probability of intercept (LPD/LPI), Morizur explained. “It is extremely difficult to intercept a laser beam because you need to be within the tunnel. You need to be within the laser beam itself,” he said. The same goes for detection—because there is no leakage from laser communications, nobody will even know where you are when you’re emitting.

This makes laser a very popular solution for government contracts and organizations like the SDA. “This is very, very strong in conflict areas where sending RF signal is basically painting yourself with a big target,” said Morizur. Lasers are also game-changing in mobile operation centers, offering significant capacity in complex environments. “This is what PWSA from the SDA has pushed forward, Proliferated Warfighter Space Architecture,” said Morizur. “There is this idea of being able to deploy lasers both in military bases, but also forward in advanced operational basis because of the benefit of discrete communication.”

To learn more about optical gateways, direct to earth (DTE) applications and use cases in maritime, listen to the full episode here.

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