On the Canary Islands last week, a team from Oerlikon Space demonstrated the feasibility of a laser link across a distance of 1.5 million kilometres for the first time ever.

In the future, laser links like this one will be able to transmit data across huge distances through the universe far more rapidly and efficiently than is possible using conventional radio links today.

To prove that data transmission across the vast distance of 1.5 million kilometres is really feasible, the Oerlikon engineers had devised a special experiment in which they set up a laser link between the islands of La Palma and Tenerife. The transmission unit was modified in such a way that the conditions on the 144-kilometre stretch between the islands exactly reflected those that would prevail on a 1.5 million kilometre link through space. This was achieved primarily by reducing the emission aperture of the laser to a diameter of less than half a millimetre in order to weaken the light signal.

The Oerlikon team installed the transmission unit in a container beside the Nordic Optical Telescope at an altitude of 2400 metres on Roque de los Muchachos, the highest mountain on La Palma in the Canary Islands. Because of the unusually clear air, this is an ideal location for optical experiments. The receiver terminal was situated in the Optical Ground Station (OGS) of the European Space Agency ESA on Tenerife.

Although the optical experiment was hampered by unfavourable weather conditions with unusually high cloud and strong winds during the first few days, a breakthrough was achieved at noon on Wednesday. The experts from Oerlikon Space succeeded in establishing a laser link between La Palma and Tenerife. In the course of the experiment, they achieved transmission rates of over 10 Mbit/sec. At this speed, it would take a mere two seconds to transmit the entire text of the Bible. The data rate would also be sufficient to transmit three digital television programmes simultaneously.

Laser-based data transmission has several advantages over conventional radio links. Because of the shorter wavelength, lasers can transmit more data than radio signals in the same period of time. Lasers can also be far more accurately aligned with the receiver than radio waves, and therefore require less power for data transmission.

These advantages are particularly useful in space applications, for instance when large quantities of data need to be transmitted rapidly back and forth between satellites. When data have to be transmitted across vast distances, too, laser communication will be the medium of choice in future. The distance of 1.5 million kilometres that was simulated on the Canary Islands is equivalent to the distance between the Earth and Lagrange points L1 and L2. These mark specific positions in space at which it is particularly advantageous to place space telescopes. Equipped with laser terminals, telescopes such as these will in future be able to transmit far greater quantities of observation data to Earth than is possible by radio today. Laser communication could also be used for transmitting data to Earth during future missions to the moon.