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.

References

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

External links

http://www.irda.org/