First optical link between satellites uses lasers

Jan. 1, 2002
For the first time, an optical data link between satellites orbiting Earth was established in November 2001 using a laser beam as a signal carrier.

The experimental optical data link was provided by the Semiconductor Laser Intersatellite Link Experiment (SILEX) communications terminal on the French Space Agency's Earth observation satellite, SPOT-4 (see figure). The SILEX terminal transmitted to a similar terminal onboard the Artemis satellite at 50 Mbit/s with a bit-error rate less than 10-9. Both terminals were built by Astrium (Toulouse, France), Europe's prime space contractor. The Artemis satellite, launched last July by the European Space Agency, is temporarily in a parking orbit at 31,000 km, while the SPOT-4 is orbiting Earth at the lower altitude of 800 km.

Zinc oxide (ZnO), a semiconductor, is potentially a gain medium for ultraviolet diode lasers. The difficulty in making the material emit light coherently stems from its high 300-kW/cm2 lasing threshold. Low-dimensional structures such as nanowires make lasing in ZnO easier by enhancing the density of states near the semiconductor band-gap edges. A group at The University of California, Berkeley, led by Richard Saykally has fabricated single optically pumped ZnO nanowires that lase at room temperature. The group characterizes the emitting nanowires with a nearfield scanning optical microscope (NSOM).

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