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Using Visible Light for Data Transfer
James Evans writes "Wired has an article about a New Zealand company which has developed a technology to transmit data at speeds up to 400Mbps up to 4km. They are working to have it more resistant to changes in weather, as well as increasing the distance. It has a number of advantages, including lack of federal regulation of the spectrum, as it is of course, visible light."
In related terrestrial networking news, waytoomuchcoffee writes "Science Blog reports that the backbone for the World's Fastest Network is up and running. It's a fiber optic 40 gigabit per second connection between Chicago and LA. Teragrid is a project by the National Science Foundation designed to link up supercomputer centers."
How long do you suppose the lack of federal regulation will last?
So, I guess we can finally have mirrors that are mirrors? Excellent!!!
"We are accountable for not only what we do, but also that which we don't do." -- Moliere
Some places do have ordinances against light pollution. I wonder how this would fit in. Also, will it come with a warning, such as "Do not look at transmitter with remaining good eye"?
Donate background CPU time to fight cancer.
they better be careful at 400mbps, they may break the switch on their flashlight.
http://hksoul.myftp.org/
Packet loss due to snow storm?
LAck of regulation is nice, but is there really a lot of regulation for InfraRed and UltraViolet?
It sounds like a VERY nice system for short-range, non-critical communictaions, but personally, I can't think of any points I would want to communicate to where I have line-of-sight... If I could get an inexpensive device that could communicate for about 10 miles, I would certainly get several.
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
Doesn't this just sound like fiber optics without the fiber?
I seem to remember this being done a long time ago. I've got an electronics book with a schematic for a serial 28k transmitter using visible light.
--Quentin
The LED-color should be chosen according to the content transferred... users sharing pr0n via P2P could build their own red-light-destrict! --- I wonder if powerful LEDs will attract insects and such - the connection speed could be reduced drastically by bugs.
I was thinking that we'll have really fast semaphore flags next.
The problem is really tired arms.
If moderation could change anything, it would be illegal.
Except with morse code, I believe, you have to find the right frequency. Not much of a problem, but likely harder to find than a little light strobing across the street. Then there's the rather obvious quote from the article
On the other hand, bad weather, or anything that might block the light's path, can cause slowdowns or power failures.
"File transfer failed: Code 75(flock of seagulls)"
*honk*
This is my sig. It's prescription, I swear. I need it for reading things... on the other side of things
Sounds like a cool technology clean, high performant, low infrastructure, does not slice limbs off or create two headed babies. This should make it a very attractive sell to commerce and to the public
I would have some security concerns though since it makes it a lot easier for those of malicious intent to intercept the signal as its basically being broadcast in the open. The technology would seem to lend itself naturally to strong encryption though.
I think they could be onto something big here.
Do not try to read the dupe, thats impossible. Instead, only try to realize the truth
What truth?
There is no dupe
So much to do, so little bandwidth.
--
Try Mozilla
Consider this, most cellphones around the world operate at 1500MHZ and so have a seemingly impressive maximum THEORECTICAL data transfer rate of 750Mbits/sec. Unfortunately due to physical contraints on modulation systems a good rule of thumb is that the actual data rate provided is about 1/2000 of this and so we end up with around 375 Kbits/sec that is just coming out with 3G systems.
You should really read up on communications theory, especially the basic stuff done by Shannon, Nyqvist and all the others.
The theoretical limit for a digital signal modulated in a perfect noiseless analog channel is infinity for any frequency! Where you get your numbers from I have no idea but they are totally incorrect!
And if you hava a noisy channel the theoretical maximum is dependent on the bandwidth and the noise, nothing else. And just because a signal hase a basefrequency of 1.5 GHz doesn't mean that it has a bandwidth of 1.5 GHz. Go check, all mobile phones have a much, much smaller bandwidth. We are talking orders of magnitude here.
But after reading the article, and seeing how they'd use LEDs (they don't say how big though), and the bandwidths involved, the lights would seem to be constanly on, do you think?
That'd mean no real lightwave pollution (it's all line-of-sight) and little visual pollution or distractions due to thousands of flashing lights?
Of course, I still have to wonder about the effects of different weather. I see it'll still work with a hand moving in front of it, but what about heavy smog days, or blizzards? Would torrential rain make problems with light refraction??
I guess it beats training swallows to carry coconuts engraved with data packets from rooftop to rooftop (they could grip 'em by the 'usks)
Hats off to the Kiwis for this one though, it sounds pretty exciting :)
Woohoo! I can't wait to see my IT Manager scaling our office building to deal with pigeons nesting on the transmitter!
"Nature will find a way..."
Great, I won't have to buy more crappy pringles in order to steal credit card numbers.. I already own a mirror..
A very important point is that Infra Red light is absorbed by the cornia (outside) of the eye and dosnt penatrate to the retina where it can cause real damage. Visable light does penetrate (obviously) to the retina and WILL fuck your eyes up. I've worked with IR lasers for a few years, they are much safer than visable light devices.
Also saying use of visable light avoids licencing isues is a bit misleading.
As to my knowlage, no country regulates visable, IR or even UV unless in lasers (or other sources) where they may get to the powers likey to cause physical danger (not very relavent here, less so with IR rather than visable light).
Put your hand up if you need a licence for your IR TV remote controal!
Anyway, a practical solution would be to use lasers of differnet wavelengths and swich to the correct one depending on weatehr conditions. EG fog attenuates some wavlengths strongly, rain scatters a differnt set of wavelengths more readily, etc (As a crude example, consider the different wavelenghs reaching your eyes from the sun in these different weather conditions)
This technique of swithing to the most aproprate wavelength for the conditions is used in army laser range finders.
Anyone quoted by a reporter knows how little they understand
Don't believe what you read is the truth.
It I am not sure how this is article bestows very interesting or novel information. Granted, the article mentions the wavelengths used are "visible", and "red". My guess is that they are emitting somewhere between 600 and 800 nm (typical visibly range is from 400 nm (purpleish) to 700 nm (red) however this is not a strict cut off, and if bright enough, even above 830 nm is visiblish).
Most telecom takes place at about 1550 nm, well into the infrared, but this is primarily because the typical fiber has nice properties in this range (absorption and dispersion). Therefore I am not sure there is much fundamental difference between infrared light telecom and visible telecom. Indeed they use very similar laser material (GaAs-based or InP-based diodes), are modulated the same way, etc.
Possibly this is neat because it is free-space optical stuff. However this (as pointed out previously) is not new. There are companies that are in place as we speek. Maybe deregulation may be of interest, but if the light it kept at the same wavelength as in fiber, then there is no need for an electronic klugey transceiver (detect the light in the fiber at 1550nm and drive a laser to re-emit the same signal at 6xx nm). Instead, an add-drop filter could be slapped on to the end, pick off the right wavelength, and feed that to a fiber which could be collimated as the source. This collimated beam then could travel over kilometers with no trouble. An all optical solution has a much
just a thought
Free air optical networking isn't really a new idea. Infrared units are pretty common. I'm not sure what supposed advantage using visible light has over infrared... IR isn't regulated (at least in the US, I can't imagine that it would be anywhere).
I investigated this for networking a couple of buildings my company had near together. Pretty cool stuff. You could get a gigabit connection over a few km of thin air. Cheaper units did 155Mb and for dirt cheap you could get 10Mb. Short range units used LEDs. Longer range ones used lasers.
I've been wondering why consumer ISP's haven't taken to this yet. It's a great last mile solution.
--Keepiru
--slashsuckATvegaDOTfurDOTcom
So what if they operate at 1500MHz? It is the bandwidth that is important. Example: Radio stations operate at 90-110MHz range. But each one has a bandwidth of around 30Khz.
So, first of all, the cellphones have a bandwidth allocated within a frequency range around 1.5Ghz. Let's take GSM, which is the most widely used standard:
In case you don't understand, it is simple. If you have a single signal at 1.5Ghz frequency, you could get a data rate equalling half the frequency. However when you transmit data you basically cause side-frequencies to appear in your spectrum. Do not assume that just because the system transmits at the base frequency of 1.5Ghz that the signal spectrum will be just a point at 1.5Ghz and 0 everywhere else. The spectrum will spread. If you use up all your possible bandwidth the spectrum will take up all the frequencies from 0 to 1.5Ghz.
Furthermore, consider the fact that there are many cellphones, sharing infrastructure. The protocol does both time-division and frequency-division multiplexing. While a *single* cellphone could perhaps work with a station at .75Gbit, this ceases to be the case when you add a few thousand cellphones. The band is subdivided to a pre-specified number of sub-bands - not only that, but there is also some time-division multiplexing going on, with each cellphone only doing rx/tx at a fraction of the total time.
Of course, the same is true for all electromagnetic wave devices.
I miss my rubber keyboard.(Homepage)
I just read about this the other day in the book "Dealers of Lightning" (page 140). While they were developing the laser printer in the 70's, some of the researchers had to move to a different building 1KM away. They had line of sight between the two locations, so they rigged up a system of lasers and photodetectors to bridge their network between the two buildings.
The beam went over a public highway, and after one woman went into a ditch after it startled her one foggy morning, they coarsened the beam to make it invisible.
They tried it in a conference. They wanted to telecast conference proceedings in a building some distance away using this method. They set up this equipment, tested everything the night before the opening day, works perfectly.
First day of conference. No signal. The receiver didn't see the transmitter at all. Total flop.
So they checked it thoroughly again that night. Everything was still working fine.
Next morning: same story. No signal.
This repeated on all 3 days of the conference.
Organizers were left scratching their heads. Funny part is, it worked at night and failed at day without their touching anything. Sabotage? The devil??
Later they found it was because the light beam was getting bent in daytime due the temperature gradient (same way that mirages occur). Poof.
Of course, these are just problems that will inevitably occur when a technology is in its nascent phase, I'm sure it'll get ironed out as it goes commercial.
The article talks about rain and fog, but is silent on the sunlight issue.
"It take 9 months to bear a child, no matter how many women you assign to the job."
A lot of infrared (IR) lasers (common examples are Nd:YAG or Ti:sapphire) operate in the near infrared
Yep, you are right. Some near IR wavelengths will be let through the cornea, and you wont have the blink reflex to protect your eye. However, this is slightly misleeding as the vast majority of IR (at wavelenghts a little further from the visable) is safe. Especially at the power levels discussed here.
The only time it decomes dangerous is when the IR light is strong enough to heat the cornea!
For example, at 1.55 microns (wavelength most suited to optical fibre) the British Standard guidelines state the maximum permisable exposure to the eye at this wavelength is the same as skin. In simple laymans terms, it has to be strong enough to burn flesh (skin or eye) before it will damage the eye!
Of couse, the real bastard lasers are UV. A fairly dangerous wavelength (suntan anyone) that you cant see. Not good for your eyes either!
Anyone quoted by a reporter knows how little they understand
Don't believe what you read is the truth.
Check out http://www.plaintree.com - they use eye safe LEDs for transmission, with speeds up to 155 MBPS, or T1/E1 at ranges to 3KM. They are using this at the Ottawa airport. They have been in business since 1988.
My rights don't need management.
UV lasers can be bad, but they don't do retinal damage at short enough wavelengths. In fact, UV is used in "Laser Vision Correction", because it ablates the cornea nicely without penetrating at all into the retina.
For really severe retinal damage, visible and near IR are the worst.
It's not wasting time, I'm educating myself.
Layer 1 security (physical access denial) is not good security. The best way to secure networks is to use secure protocols - wrap everything up in SSL.
As for the service interruption concern, it would seem prudent to use several redundant beams spaced at irregular vertical and horizontal intervals - wide enough so that a small flock of pigeons doesn't interrupt service.
I was driving to work North on Willows Rd in Redmond, WA today and I saw Terabeam's laser flashing away. It is pointed almost directly along the road to their satellite building to the South.
I haven't noticed it before, so I wondered if they had some beam dispersement issues. I got a little concerned that the laser was damaging my eyes. Hopefully the power on the lazer diode is turned down. You never know what is going on in development hardware ;)
The light looks like your run of the mill strobe light. The pattern looks like the LEDs on your hub. Not sure why because that flash speed is not consistent with the marketing info on www.terabeam.com.
Unfortunately the fog here in the valley tends to prohibit their use of the system.
Holland