TNO and partners send data over 10 km ground-to-ground laser link

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A consortium led by TNO has established a laser communication link over 10 kilometers between the test site at the Royal Netherlands Meteorological Institute (KNMI) in Lopik and the Gerbrandy tower in IJsselstein. According to the partners of the Terabit Optical Communication Adaptive Terminal (Tomcat) project, it’s the first time a robust optical data connection has been set up in real-world conditions compatible with conventional infrastructure. They view the successful demonstration as a big step towards a commercial optical ground station and faster and more secure broadband connectivity in the Netherlands and Europe.

The space terminal breadboard at 226 m altitude in the Gerbrandy tower. Credit: TNO
The optical ground station demonstrator at the KNMI test site. Credit TNO

Using lasers to directly link satellites and connect satellites and ground terminals, information is sent and received to and from Earth. Moving from the radio frequencies currently employed for global communications to optical would allow transferring 1,000 times more data. The new technology also avoids the issues with the limited RF spectrum availability and the ensuing expensive licensing. Furthermore, the usage of very narrow optical beams instead of wide radio signals makes communication more secure. As eavesdroppers need to be in the direct path of the beam, their efforts are more complicated and more easily detectable.

When light moves between Earth’s surface and space, however, it gets distorted due to the fluctuations in the atmosphere. One of the innovative elements of the Tomcat system is its ability to pre-correct the laser light with adaptive optics. The distortion of the received laser light from the satellite is measured and by applying the inverse of this distortion to the transmitted light, a robust communication link can be established. Other key technologies are thermally stable optomechanics, high-power photonics and high-throughput optical transceivers.

In terms of disturbances, the closest resemblance of a ground-to-space link at 39,000 km altitude is a ground-to-ground connection over 10 km with the satellite terminal placed on a high location (like the Gerbrandy tower). The recent Tomcat field test involved the full optical communication chain, starting from an RF signal, converting it to the optical domain and back again. A combination of technologies employed in the demonstrator enabled a virtually error-free data transfer for multiple minutes in the relatively harsh turbulence conditions of the ground-to-ground link.

Implemented with support from ESA’s Artes ScyLight program and funded by the Netherlands Space Office, the Tomcat project includes TNO, Dutch partners AAC Hyperion, Airbus Defence and Space Netherlands, Celestia STS, Cellnex, Demcon, Hittech Multin, KNMI and VDL ETG, SES from Luxembourg, Airbus DS SAS and Eutelsal from France and MPB Communications from Canada. The successful test paves the way for the development of an in-orbit demonstrator led by Airbus Defence and Space Netherlands, which is expected to be ready in 2023/2024. In the years after that, a consortium of Dutch and European companies, headed again by Airbus Defence and Space Netherlands, is to bring the technology to the market as a final product enabling terabit per second data transfers.