Free-space optical communication

Free-space optical communication involves the use of optical links across the space between two points, either within the Earth's atmosphere, or in outer space.

The optical links usually use laser light, althogh low-data-rate communication over short distances is possible using LEDs. IrDA is a very simple form of free-space optical communications.

For longer distances, a pair of telescopes is used at each end, with a laser and photosensors mounted in each telescope.

Free-space optical communications has a number of uses:

• as a last mile telecommunications link
• as a LAN link between buildings
• for communications between spacecraft, including elements of a satellite constellation
• for interstellar communication

For terrestrial applications, the limiting factors are the attenuation of the beam by:

• beam dispersion
• atmospheric absorption
• rain (severe rain may have up to 100 dB/km attenuation)
• fog
• snow
• scintillation

For space applications, none of these defects applies, and free-space optical communications is potentially usable at interstellar distances.

See also: optical window, radio window, Free-space loss, Rayleigh scattering, Mie scattering

References

• Kontogeorgakis, Christos; Millimeter Through Visible Frequency Waves Through Aerosols-Particle Modeling, Reflectivity and Attenuation

External links

• http://www.irda.org/