Researchers Unveil High-Speed Laser Communications Device For Space 40
coondoggie writes "Using lasers to communicate quickly through the long distances of space has generally been the purview of science fiction. But researchers at the National Institute of Standards and Technology (NIST) and NASA's Jet Propulsion Laboratory (JPL) are out to change that notion with a prototype array (pdf) that can read more information — and allow much higher data rates than conventional systems — than usual from single particles of light. Lasers can transmit only very low light levels across vast distances, so signals need to contain as much information as possible, NASA said."
Not *that* new (Score:5, Informative)
Using lasers to communicate quickly through the long distances of space has generally been the purview of science fiction.
The ESA Artemis satellite [wikipedia.org] used the SILEX laser link to communicate with the SPOT-4 satellite. It was not the first project to use laser communications in space either. The datarates mentioned in this article are better than those of SILEX though.
photons are photons (Score:2, Informative)
Does it matter whether the emitted photons are from RF or Light? They both travel at the same speed.
Re:photons are photons (Score:5, Informative)
Yes. The energy that gets you one single green photon gets you 75000 radio photons at the Cassini probe's X-band comm frequencies, for example. Having 75000 times more quanta means your system can be built on well-known classical principles (i.e. standard microwave radios) and work as expected.
But can one green photon hold more information than an RF photon?
The trick is when you're talking about bandwidth. "A key characteristic of bandwidth is that any band of a given width can carry the same amount of information, regardless of where that band is located in the frequency spectrum." Visible light is approximately "430–790 THz." While X-Band is "8.0 to 12.0 GHz" So you're talking about hundreds of THz vs 4 GHz.
Nyquist says the absolute maximum symbol rate is equal to twice the bandwidth. This means that once you've hit that cap, the only way to send more data is to either increase the number of bits per symbol or increase the frequency. Increasing the symbol rate can end up taking expensive delicate equipment, so it's easier to just throw a second transceiver at the problem. The second one would be exactly like the first, but would be operating at a slightly different frequency. The spectrum for light is a much larger playground for this than X-Band is.
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