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Project to build terabit optical links to space

Technology News |
By Nick Flaherty


The second phase of the TOmCAT (Terabit Optical Communication Adaptive Terminal) project will enable secure high-throughput laser communication between ground stations and satellites in space and is led by TNO Space & Scientific Instrumentation.

This phase of the project brings together Airbus Defence & Space Netherlands, FSO Instruments, Hittech Multin, Celestia-STS, MPB Communications and satellite operators Eutelsat and SES alongside ESA and the Canadian Space Agency.

The project has to develop technologies including high-bandwidth adaptive optics, thermally stable opto-mechanics, high-power photonics and high-throughput optical transceivers.

One of the key elements of TOmCAT is its ability to pre-correct the laser light with adaptive optics. When light moves between the surface of the Earth and space, it gets distorted due to the fluctuations in the atmosphere. TOmCAT measures the distortion of the received laser light from the satellite, and by applying the inverse of this distortion to the transmitted light, a robust communication link can be established. This requires high speed adaptive optics.

The system has to generate 650 W of optical power, levels that are high enough to burn any contamination on the mirrors and lenses that track the satellites 36 000 km away in orbit. The accuracy and stability of the moving mirrors satellites needs to be in the order of sub-micro-radian to provide the multiple wavelength multiplexed lasers, each generating 100 Gbit/s of throughput. An opto-mechanical system consisting of a bulk multiplexer, adaptive optics system and a 60 cm telescope are developed, each providing the required stability and accuracy while handling the high optical power levels.  

The design, completed in the first phase of the project, uses a ‘digitally transparent’ architecture where RF signals will be sampled and modulated onto the optical domain by a digital signal processor. High power optical Amplifiers (EDFAs) boost the optical signals to high power levels in the order of 50 Watts per channel.

Next: 10km demonstrator


To achieve the terabit/s throughput, multiple wavelengths are then multiplexed into two very high power optical free space beams. An Adaptive Optics system pre-corrects the optical wavefront to compensate for the expected atmospheric turbulences and a telescope transmits the high power beams to the geostationary satellite.

A downlink implementing a similar architecture enables a bi-directional optical feeder link. The satellite provides communications services to end-users through hundreds of RF spot beams, where each spot beam serves a geographic area on Earth for 5G backhaul.

The project will implement the design of the end-to-end Optical Feeder Link for high-throughput satellites and build and test the technologies required for future Terabit Optical Ground Stations. A 10 km ground-to-ground link will demonstrate the technical feasibility of future terabit-per-second laser communication between ground and satellite terminals.

The project will also position Airbus DS NL as future Original Equipment Manufacturer (OEM) for the Optical Ground Terminals and Optical Ground Stations.

www.tno.nl

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