For around 100 years wireless data transmission has been realised with microwave technology for many applications. Now, it is time to extend the physical layer by optical communication. This technology extension is supported by high demand in connectivity for data exchange. It is covering various possible links, such as those between airplanes and satellites, links from space to ground station on earth, or simply data transmission between satellites.
Optical communication is offering five major advantages versus microwave technology:
• transmission cost per bit is significantly lower,
• total capacity can be increased,
• no license approval is required,
• excellent beam steering over hemisphere, and
• bridging of long distance, up to 80,000 km approved.
Status of Technology
In 2016, inter-satellite data transmission between two LEO satellites was approved. Every satellite was equipped with a Laser Communication Terminal (LCT). When the two satellites are in visibility range, they start to transmit data at 5.6 Gbps over an 8,000 km distance. This success was a key milestone in free space optical communication. Finally, it is the confirmation that technology is ready, and it kicks off a myriad of innovations, ideas for applications, or just the empowering to take the next step.
Currently, a high data network, the European Data Relay Satellite System, (EDRS) is in service since 2014. With 1.8 Gbps, data is transmitted from several LEO to GEO satellites by laser communication. The advantage of having increased access time to LEO satellites provides a real-time opportunity of data availability. The network will be extended in the next couple of years by more LEO satellites.
Now, there is a broad portfolio in the market, covering specific application and market requests:
• One portfolio stream is targeting the optical communication links between ground station on earth and LEO or GEO satellites. In 2020, the first link between the ISS (International Space Station) will go in service and will provide a data connection
of 10 Gbps. Another R&D stream is to provide a data link to space data networks up 100 Gbps and higher to distribute data around the world.
• For small CubeSat satellites, a low-cost product approach is supporting many applications with 100 Mbps. The small size of 10 cm x 10 cm and the height of 3 cm indicate the integrated approach and the capability of optical communication.
• To support global data network in space for LEO constellations, special laser terminals are in the final stage of development. They have a data rate of 10 Gbps, and the upgrade to 100 Gbps is in predevelopment. Due to the increased production volume and use of integrated optics, the cost of transmitting a Gbit/km is in the range of a few dollars. In order to achieve this target, industry has established a supply chain with most efficient production and manufacturing techniques.
Finally, we are observing growing data networks around the world that need less support from ground station or gateways. Data can be forwarded independently to every place on earth without interfering with national interests, with shorter delays and more secured connectivity.
An additional benefit of optical communication is the support of quantum cryptography. Transferring data with the secured protection of privacy is pivotal in order to avoid cyber attacks in sensitive communication links.