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.
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Hence the use of the word 'generally' rather than 'exclusively'.
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And LADEE [nasa.gov] recently demonstrated a laser communications system with data rates about ten times over what Artemis demonstrated.
I think these articles and summaries that appear on Slashdot would better serve the community if they took a moment to figure out what the new part of "the news" really is. This sounds like an improvement which will enable more efficient laser communication over longer distances than was demonstrated with LADEE. So, an improvement more applicable to deep space probes or maybe all
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.
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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.
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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Conversely, optical comms could probably be received on any telescope on the planet. We already have a wide variety of equipment setup for receiving very faint optical signals. Just a matter of hooking that into a modulator (he says, casually describing several Ph D projects and millions of dollars).
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I think the equipment is of comparable reliability: doped fiber amplifiers, etc. are standard items. We've been flying pretty exotic lasers for a lot of years.
But wouldn't the fibers locally degrade over the years of being exposed to the effects of galactic radiation (heavy ion bombardment outside Earth's magnetosphere), paving way to some sort of local cascade failure (given the EM energy densities involved)? Klystrons don't face nearly the same issues.
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Surely many of the existing encoding techniques used by existing broadband and old school modems (Yes I do know what BAUD is) would be valid here. In fact I believe many of the ideas you suggest are actually already being used by the Telco's especially utilising discreet frequencies.
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Nope, nothing new to the Telcos or pretty much anyone who had to take a Signals course. The Nyquist rate has been known singe Harry Nyquist published it in 1928. The trick is that it sets a maximum number of symbols as twice the bandwidth. If you're only using one symbol (a '1' or '0') then the baud (symbol) rate is equal to the bit rate. If you're using more symbols like in modern systems (eg. 64QAM) then the baud rate doesn't change, but the bit rate (in Mbps) goes up exponentially.
Combining multiple
optical multiplexing... (Score:3)
...also exploits polarization to a high degree. In fact, many developmental optical communication systems exploit polarization purity for higher base digital transmission, and even if polarization modulation slows things down for some schemes, the resulting bandwidth can overcome the obstacles by an order of magnitude or more over the reduced rate of the mux/demux. The issues with these schemes is more about cost. But most of these programs are directed at n-fold increases in existing optical fiber networ
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I'm only familiar with nyquist when it comes to audio phenomina... but if you're using more than half the bandwidth won't you have to deal with artifacting (aliasing in the audio world)?
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I'm only familiar with nyquist when it comes to audio phenomina... but if you're using more than half the bandwidth won't you have to deal with artifacting (aliasing in the audio world)?
Nope. The Nyquist-Shannon theorem deals with sampling rate. It says you have to be sampling at least twice as fast as the highest frequency if you want to perfectly decode the signal. The Nyquist rate deals with the maximum amount of data that can be transmitted. It says the absolute maximum symbol rate is equal to twice the bandwidth.
It's an easy mistake to make because the first is often called the "Nyquist sampling theorem," and they both deal closely with the same concepts. The wiki page I original
There's a huge difference in directivity (Score:2)
Even out of a high-gain antenna radio waves spread enough to lower EIRP a lot compared to a laser.
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It's hard to collimate signals in the microwave band. There is no way to do that and if there were there are still order of magnitude frequency issues. For about a hundred bucks I could buy a laser and create a way to bounce a data signal off of Mars with it using a mirror and a speaker. From here, using retail parts. The coherent part of lasers is freaking awesome.
Did you know lasers can be used as propulsion too? We aren't making enough use of that.
About Time! (Score:1)
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I've invested way too much time to movies and books to not see laser communications, to at the very least, to the moon in my lifetime. There are many authors that have enjoyed my 25 cents or less of royalties they received that should finally be vindicated by including laser based communications in their books!
to...to... to.. damnit..
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to...to... to..
...c'mon and do the conga.
Frickin' Laz0rz! (Score:1)
Does it have a Shark2Shark protocol (S2S) implemented?
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Why would a shark need to control another shark?
Naturally the protocol is Shark to Master (S2M)
high-speed-wifi vs high-speed-lasers (Score:1)
I've found that most WiFi connections bragging about being highspeed, are not that far from being modem speeds. If it's high-speed, the marketers feel the terminology forces the users into giving them more cash. Evey time I here the phrase, I figuartively want to randomly strangle someone, anyone working in sales.
Lasers at modem speeds; there's a thought, or not.
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under two assumptions
1) you are talking about telephone modems
2) you are talking about WiFi connections, backed by a internet service that is not through a telephone modem
you must either have only used some astoundingly awesome modems, or some astoundingly crappy WiFi routers
the only case where they have remotely similar speeds is if you are comparing the text-only response via modem to a full web page with a bunch of images along with similar text.
High-speed? High bitrate... (Score:2)
...unless their laser can send signals traveling faster than the speed of light.
Delay-tolerant networking? (Score:1)
Hard To Aim (Score:3)
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Key points
- They use superconducting nanowires to make a grid. I doubt anybody not in space is doing that
- Though I didn't catch it from the pdf, the article has a quote from NIST saying that x,y information inside this grid
- This allows an n x n pixel grid sensor to be built out of only 2n nanowires. A photon heats up a nanowire intersection to register a hit, then wait for it to cool down. p.s. cooling something down isn't that easy in space.
- Presumably you would have to beam a repeating pattern (or holo
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... that x,y info in the grid is used to encode additional information, which allows you more info not *despite* but *because* only one photon hits the detector at a time. In other words this detector only works when only one photon can reach the detector at the same time, and the beam output will have to be weakened if the spacecraft is too close perhaps. So if the photon rate is 1 photon per millisecond the bit rate can be multiples of 1000 bps due to also having an extra couple of bits per photon saying