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Researchers Unveil High-Speed Laser Communications Device For Space

samzenpus posted about 2 months ago | from the saving-your-laser-minutes dept.

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."

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40 comments

Usenet is the new Slashdot, see you in comp.misc! (-1, Offtopic)

RocketRabbit (830691) | about 2 months ago | (#46235779)

Usenet is the new Slashdot, see you in comp.misc! Get your free Usenet account at Eternal September and never worry about beta again, on the original censorship-free, non-commercial, distributed forum.

See you all on comp.misc!

Not *that* new (4, Informative)

cheesybagel (670288) | about 2 months ago | (#46235789)

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.

Re:Not *that* new (2)

bigpat (158134) | about 2 months ago | (#46237747)

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 allow the packing of more sensors on Earth observing satellites which will then have more bandwidth to transmit all that data.

photons are photons (2, Informative)

Anonymous Coward | about 2 months ago | (#46235791)

Does it matter whether the emitted photons are from RF or Light? They both travel at the same speed.

Re:photons are photons (1)

Anonymous Coward | about 2 months ago | (#46235843)

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 (0)

Anonymous Coward | about 2 months ago | (#46235875)

But can one green photon hold more information than an RF photon?

Re:photons are photons (4, Informative)

EmperorArthur (1113223) | about 2 months ago | (#46236193)

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.

https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]

Re:photons are photons (1)

K. S. Kyosuke (729550) | about 2 months ago | (#46236599)

I'm not an expert on this, but isn't thing whole thing dependent on energy? The whole reason for Voyager probes communicating slower and slower with us as they got farther and farther away was the signal-to-noise ratio, not some idealistic capability of a frequency-limited analog band. And the fact is that we can still manufacture high-powered microwave equipment more easily and reliably than high-powered CW lasers for communication (and spacecrafts seem to be all about reliability these days - state-of-the-art equipment doesn't seem to work all that well in space).

energy limits for deep space comm (0)

Anonymous Coward | about 2 months ago | (#46236953)

Yes.. deep space links today are energy limited, not bandwidth limited. However, optical comm helps in another way related to the energy: you can make a narrower transmit beam with a limited size device, so you can squirt the limited energy you have in narrower beam, increasing the effective isotropic radiated power (EIRP).

To a first order, the beamwidth is 70/diameter in wavelengths So going from 3 meters at Ka band (32 Ghz, 1cm wavelength, 0.3 degree beamwidth) to 50cm at 500 nm (1,000,000 wavelengths diameter, some incredibly small beamwidth) helps a lot. (practical optical systems can't do that well).

Of course, now you have to point that very, very narrow beam, which is non-trivial. Spacecraft vibration is an issue, knowing where to point is another. When your beam is 0.3 degrees wide, you can point in the general direction of earth and call it done. But when your beam is 1 microradian wide, and you're a billion km away (Saturn), the "spot" is 1000km wide: not only do you have to point it at Earth, you have to point it at the right place on earth.

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.

It's more that the whole system isn't really mature or available. You've got a set of microwave receiving stations (DSN) that have been around for 40 years, gradually upgraded, so a mission that wants to use radio has existing infrastructure to use. There's no similar infrastructure of optical receiving terminals (yet).

Re:energy limits for deep space comm (1)

Electricity Likes Me (1098643) | about 2 months ago | (#46237003)

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).

Re:energy limits for deep space comm (1)

K. S. Kyosuke (729550) | about 2 months ago | (#46239275)

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.

Re:photons are photons (1)

Big Hairy Ian (1155547) | about 2 months ago | (#46237213)

Sorry but that's just making me Baud :)

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.

Re:photons are photons (1)

EmperorArthur (1113223) | about 2 months ago | (#46238227)

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 transceivers which each use the same bandwidth but with different frequencies is also very common. It's a form of multiplexing, and is how many cell phones and cable modems can share the same wire without reducing throughput.

https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]

optical multiplexing... (2)

sugarmatic (232216) | about 2 months ago | (#46238869)

...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 network bandwidth. Their time will come.

Re:photons are photons (1)

X0563511 (793323) | about 2 months ago | (#46237721)

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)?

Re:photons are photons (1)

EmperorArthur (1113223) | about 2 months ago | (#46237993)

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 originally linked to was the Shannon–Hartley theorem, which is an adaptation to the Nyquist rate to account for noise reducing the theoretical maximum. It also explains Nyquist rate better than the actual Nyquist Rate wiki page. :/

https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]

Re:photons are photons (0)

symbolset (646467) | about 2 months ago | (#46236211)

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.

Re:photons are photons (0)

Anonymous Coward | about 2 months ago | (#46237139)

Beyond a couple hundred kilometers, that laser you buy for a couple hundred bucks and a parabolic radio antenna will both be collimated in a way that drops off with r^2. If you were using say a 532 nm laser, and had some pristine 40 cm diameter optics (which would cost a lot more than your laser) and ignoring atmospheric disturbance, at just the Earth-moon distance the light intensity would be about a factor of 3 million weaker. At its closest to Earth, Mars would be getting a trillionth of the light intensity, which while in principle is detectable, would not be trivial and would have very limited bandwidth (less than a Mbit/s assuming it can capture every photon perfectly).

While lasers are better collimated than radio signals because of their smaller wavelength, the smaller wavelength also means optics are much more expensive and need to be designed to tighter tolerances (e.g. making foldable antennas much harder and heavier), and you will pay a lot more to get similar transmission powers.

Re:photons are photons (0)

Anonymous Coward | about 2 months ago | (#46237651)

Ever hear of a MASER? Is there no end to your propensity to expound at length on subjects you know nothing about?

Re:photons are photons (0)

Anonymous Coward | about 2 months ago | (#46239117)

The beam divergence of even a good laser is on the order of 1 milliradian, which would be a spot 25000km in radius at an earth-mars distance of 50M km. Supposing this laser starts with 1W of red photons that all makes it to space, you're depositing 1800 photons/second per square meter on Mars.

Replace the meterish directional antenna with a square meter astronomy-grade telescope and you've nominally got about 1800 photons/second. At that rate, quantum effects will bite your heel every step of the way: Since photons are distributed statistically about randomly within the spot, your uncertainty in received signal intensity is O(1/sqrt(n)) so you know the photon rate to within about 2%. Observing the earth laser for 1 second on mars would let us discern any of about 50 intensities, which carries 50 * (however much information you can fit into a packet's worth) bits of data.

Which is impressive in that it would nominally work for teletype-level links. For reference, an X-band uplink with 1* radius beam divergence at 10KW transmit power is roughly 400 million radio photons/m^2-second on Mars, hence why even interplanetary radio can ignore quantum effects like shot noise.

About Time! (1)

Seranfall (680430) | about 2 months ago | (#46235803)

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!

Re:About Time! (2)

Seranfall (680430) | about 2 months ago | (#46235807)

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..

Re:About Time! (0)

Anonymous Coward | about 2 months ago | (#46236053)

This was already done in 1968.
http://en.wikipedia.org/wiki/Surveyor_7

"On January 20, while the craft was still in daylight, the TV camera clearly saw two laser beams aimed at it from the night side of the crescent Earth, one from Kitt Peak National Observatory, Tucson, Arizona, and the other at Table Mountain at Wrightwood, California."

Frickin' Laz0rz! (1)

Anonymous Coward | about 2 months ago | (#46235889)

Does it have a Shark2Shark protocol (S2S) implemented?

Who should get the attention? (0)

Anonymous Coward | about 2 months ago | (#46235997)

Funny that this news release is from NIST/JPL, when LLCD came from Lincoln Labs/Goddard http://esc.gsfc.nasa.gov/267/271/Space-Terminal.html

high-speed-wifi vs high-speed-lasers (1)

Anonymous Coward | about 2 months ago | (#46236011)

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.

Re:high-speed-wifi vs high-speed-lasers (1)

davester666 (731373) | about 2 months ago | (#46236181)

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.

Re:high-speed-wifi vs high-speed-lasers (0)

Anonymous Coward | about 2 months ago | (#46236973)

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.

Most highspeedwifi being offered as a leader loss to attract customers aren't using crappy routers, they're just capped to run crappy to save on bandwidth costs. Starbucks, FedEx Kinkos and a few middle level hotel chains, on bad days -- in a lot of different places I've been within the US, run at 15 to 20 kbs. On an average day, it's in the 50 to 60 kbs range; if you're really lucky, occasionally they will momentarily bless your experience with120 kbs (or more).

The reference to modems was meant to be an aspersion, not the above technical analogy that I completely understand; it seems avoiding the tangential issue may have been a better thing to do; instead, to cynically speak of an imaginary future: Now that the idea of the internet using lasers at highspeed has been established, maybe it'll be an easier route for the marketers to start putting caps on that technology.

High-speed? High bitrate... (2)

Anonymous Coward | about 2 months ago | (#46236123)

...unless their laser can send signals traveling faster than the speed of light.

Hard To Aim (2)

Githaron (2462596) | about 2 months ago | (#46238207)

According to the article, they use positioning information to generate additional bits of information. My question is how do they determine position at large distances when both bodies are obviously not standing still. The only thing I can think of is having one constant laser being used as a position reference for all communication lasers. Of course, they still have to be able to hold the laser on the detector array.

Re:Hard To Aim (1)

mattr (78516) | about 2 months ago | (#46245169)

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 hologram?) covering a broad area, and the pattern resolution would be adjusted as distance to target spacecraft changes over time.
   

Re:Hard To Aim (1)

mattr (78516) | about 2 months ago | (#46245227)

... 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 which grid cell (pixel) the photon hit.

This has already been done, and is being done, eve (0)

Anonymous Coward | about 2 months ago | (#46238751)

....by the folks in a nondescript campus near the base of Haleakela, for transmission from their rather large facility on the top of the mountain. The building says it is a defense contractor...but most of the folks inside are AF. The clients are military and various three letter acronyms.

If you are in the area looking like you know what you might be doing with fancy, uncommon sorts of cameras that may or may not image certain wavelengths, you will be asked to leave, public property or private.

Not that I would know anything at all about that, of course.

Inventor's Check List (0)

Anonymous Coward | about a month ago | (#46260647)

Let's see:

High Speed WiFi >> Check

High Speed Lasers >> Check

High Speed Warp Drive >> Still a To Do; must invent regular warp drive first.

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