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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."
So much to do, so little bandwidth.
--
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Some places do have ordinances against light pollution. I wonder how this would fit in.
Usually "light pollution" is considered to be lighting up the sky.
Also, will it come with a warning, such as "Do not look at transmitter with remaining good eye"?
The system uses LEDs not lasers.
Sounds awfully like the old telecom's monopolies in Europe (hanging an ethernet cable out of your window and into your neighbor's for a LAN party was illegal, because only the state operated telecoms had the right to establish communications across property lines), and has AFAIK nothing to do with usage of spectrum. Encroaching on a frequency that is not you are not licensed to use is illegal, even if both (intended) endpoints of communication are on the same property.
FYI, visible light is roughly 400 to 700 terahertz.
If I could get an inexpensive device that could communicate for about 10 miles,
Well off the top of my head I'd say that if you made a device like a colimater which is basicaly t telescope the light is shined thru backwards it would greatly increse the range. All of the light would be packed into a beam, Mirrors up to 10 inches in diameter and accurate to 1/10 wave are available. This would send a beam 10 inches in dia so any obstructions from snow would be much less likely. Amature astromomers make their own mirror, some times as large as 18 inches in dia. after that its a matter of just pumping enough power thru the thing.
The thing wouldn't be completely reliable, but I'd bet that when the system goes down the weather would be so bad that not many people would be at work anyways.
Apocalypse Cancelled, Sorry, No Ticket Refunds
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
sorry it's never go over the horizon, if go can't see there with your own eyes it wouldn't go. putting the transmitter and recievers up on towers and repeaters will help but it's still line-of-sight. it's cool for "last mile" stuff but probably no-good for long-haul
Apocalypse Cancelled, Sorry, No Ticket Refunds
Well, we just shut the laser on and off and did not modulate, anyway speeds of > 1Gbit should be possible with this simple technology. The problems of this design are the adjustment, free line of sight (weather, insects, birds), eye safety, other light sources (sun!) and a very sensitive receiver circuit.
The maximum range is infinite but it can be limited by the protocol (e.g. Ethernet) due to collision windows.
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.
Not only illegal, but pretty dumb as the houses would have a different grounding and therefore the ethernet cable you've dropped between the houses could end up as the grounding for one of the houses (remember that part about current always taking the easiest route from HS?).
If you want to have your computer/network equipment fried, go ahead and drop what ever you like out the window.
To be on the safe side, drop wireless or optical out the window as optical cables doesn't transmit electricity...
"It take 9 months to bear a child, no matter how many women you assign to the job."
Not exactly, if you (theoretically) modulate a 1.5 gig signal with a signal at half that frequency, two sidebands appear in this case from 0.75 gig to 2.25 gig is the resulting signal spread. So if you use all your possible bandwidth (and again this is theoretical, I know of no system that 'coud' do this) then a bandwidth of 0-3gig will result. Interestingly, in this scenario (ie FM or AM modulation) the bandwidth consumed is double what the maximum modulating frequency is. So one sideband is 'wasted' as it carries a mirror of the others information. Also the carrier frequency itself is redundant, it carries no useful information. Given these facts, Single Side Band (SSB) is much more efficient in terms of bandwidth & power required (power saved in the transmission of carrier & one sideband can be used to increase the remaining sideband)
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uhhhh... ethernet is transformer-isolated, no?
Last time I was there roads were called, in general, "roads". A Motorway (this is the same naming as the UK, where I assume it came from) is equivalent to a US Freeway or German Autobahn.
:)
As another FYI, when I was last there, there was only one Motorway in the whole of NZ
---- Den ene knappen er powerknapp, den andre er Bender voice knapp "Bite My Shiny Metal Ass"
this technology has been available for decades, it's called free space optical datacom. As the link points out, there's even a google directory listing for providers of this technology.
there are significant limitations on this tech however. cheif among them is reliability in various weather conditions. rain, fog, snow, and passing birds tend to cause havok with a laser beam. setting a laser up to point to a target 1 or 2 kilometers away is no small feat, and even harder is making sure it stays on target months and years later.
there's a reason why most wireless shorthaul links use microwaves, as the laser technology really doesn't work very well.
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.
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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.
The astronomers push for using sodium vapor lamps that exhibit a very narrow emission spectrum. Very nearly all of the light is concentrated in two very close together spectral lines - hence they can easily filter out all of the streetlights with a simple filter.
The more common mercury vapor lights have a much broader emission spectrum, therefore making filtering out their light much more difficult.
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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
Are you aware that the link you provided says the exact opposite of what you claim?