Using the Terahertz Spectrum for Wireless Communication

holy_calamity writes "A first step to allowing wireless data transfer over a currently unused part of the electromagnetic spectrum is reported in New Scientist. Terahertz radiation exists between radio and infrared. A new filter created at the University of Utah can filter out particular frequencies, a prerequisite for using it for data. The abstract of the paper in the journal Nature is freely available."

Comments

It might just take a while

[NixieBunny]

I work on radiotelescopes that work at several hundreds of gigahertz, and the technology used there is rather exotic. There is also the slight problem of water absorption of the signal - our telescope at 10,500 ft (3200m) altitude has trouble getting a clear shot to space due to the atmosphere, so communication would have to be rather short-haul as in LAN.

Re:It might just take a while

[Anonymous Coward]

...so communication would have to be rather short-haul as in LAN.

Perhaps TFA should have mentioned that.
 
Wait...

Re:It might just take a while

[FMota91]

Well, if Internet speeds keep getting better (which I'm sure they will), this could be used to make a faster Wi-Fi router. It shouldn't be too difficult in a few years. Amirite?

Admittedly, I don't know if I am.

Re:It might just take a while

[evilviper]

There is also the slight problem of water absorption of the signal [...] so communication would have to be rather short-haul as in LAN.

Which is EXACTLY what TFA said...

But hey, what do I know, your post is a +5, so it must be somehow insightful, not 100% redundant.

Re:It might just take a while

[NixieBunny]

Are you kidding? you can't do first post if you RTFA!

Re:It might just take a while

[psaunders]

Sounds like NRAO-ALMA.

*sigh* It irks me whenever someone posts an obscure acronym without expanding it. Seriously, it's just rude.

For the uninitiated, that is Nothing Really Amazing in Outerspace - Alien Life My Ass.

Re:It might just take a while

[cyphercell]

Ok so this would only be effective in a LAN type of situation but just as a question, wouldn't this free up some frequencies in the long run? Also does anyone have any idea on the possible ranges for point to point vs point to multi point? I'm thinking if the cost of these things goes down (a lot) and a point to point connection can get out to about a mile then point to multi point ought to cover a block, then we may have a future with these things on top of telephone poles. The distance for wimax is typically 7.5 to 1 with point to point covering the most distance.

Re:It might just take a while

[Profane MuthaFucka]

LAN? Fuck, I'd be happy if I had terahertz communication two inches from my CPU to my memory. And terahertz memory. And a terahertz CPU.

Re:It might just take a while

[DarkAxi0m]

or... it could be for Atacama Large Millimeter/submillimeter Array - National Radio Astronomy Observatory :P

http://www.alma.nrao.edu/

Google can be your friend too.. .

Re:It might just take a while

[DarkAxi0m]

Ooo my bad, looks like Google was lying to me so would be his friend.

guess i should read things before i reach for the Ctrl-C Ctrl-V

Re:It might just take a while

[Exocrist]

All the better if he's dead on, that just saves the rest of us from having to RTFA!

Re:It might just take a while

[alphamugwump]

Except everyone has firehose now, so you don't need to subscribe.

Re:It might just take a while

[FuzzyDaddy]

http://www.gigabeam.com/technology.cfm has a nice plot of atmospheric absorption versus wavelength. For reference, 100 dB/Km = 3 dB/30 meters - or 50% signal strength loss per 30 meters, not counting the 1/r^2 factor.

Also, generating and modulating signals, with current technology, is done by firing very expensive lasers at very customized pieces of semiconductor materials. As for receivers, NixieBunny would know better then me what the current technology cost and noise figures would be.

All of which to say, this is an interesting article, but it's about 1% of the way towards communications in this band.

Don't get me wrong - this is a cool paper, looks like good work, and this might have some very interesting technological applications. But the perpetual question of "what is it good for?" that every reporter asks (it's got to be a law or something) about every scientific advance misses the point. We don't know what it's good for, but it expands our knowledge of the world, and that can only help us.

Using it for something is the job of the next genius. These guys did enough by getting it to work. Someone else will have to figure out what it's good for.

Re:It might just take a while

[mdsolar]

This type of technology (but with regular arrays) has already found application is space: http://www.iso.esac.esa.int/manuals/HANDBOOK/lws_h b/node14.html. Water vapor is not a big concern there.
--
Tap the Sun: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html

Re:It might just take a while

[skarphace]

Well, if Internet speeds keep getting better (which I'm sure they will), this could be used to make a faster Wi-Fi router. It shouldn't be too difficult in a few years. Amirite?

First off, there's no such thing as a 'Wi-Fi router'. At least not in the technical sense. My guess is some marketing genius decided that was a good name for an AP/Router combo.

Anyway... this tech looks like it would be fairly poor as an omni-directional access point. While you can fit more data on a frequency that high, it's got a very short distance before attenuation, absorption, and interference sets in. You could ramp up the power to counteract that somewhat but the FCC hates that kind of thing. But even as they're describing meta-material filters, my guess is that this is more of a directional style transceiver. This would probably be best suited for use between campus buildings(WAN).

So, when will this be mismanaged by the Government

[Kid Zero]

10 years? Anyone?

Geek into English.

[Anonymous Coward]

"Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films1 has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission2. The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons (collective electronic excitations in the metal surface) mediate light transmission through the grating1, 3. In this picture, structural periodicity is perceived to be crucial in forming the transmission resonances. Here we demonstrate experimentally that, in contrast to the conventional view, sharp transmission resonances can be obtained from aperiodic aperture arrays. Terahertz transmission resonances are observed from several arrays in metallic films that exhibit unusual local n-fold rotational symmetries, where n = 10, 12, 18, 40 and 120. This is accomplished by using quasicrystals with long-range order, as well as a new type of 'quasicrystal approximates' in which the long-range order is somewhat relaxed. We find that strong transmission resonances also form in these aperiodic structures, at frequencies that closely match the discrete Fourier transform vectors in the aperture array structure factor. The shape of these resonances arises from Fano interference4 of the discrete resonances and the non-resonant transmission band continuum related to the individual holes5. Our approach expands potential design parameters for aperture arrays that are aperiodic but contain discrete Fourier transform vectors, and opens new avenues for optoelectronic devices."

Alright, how many here can translate that into english?

Re:Geek into English.

[rhythmx]

Basically it says that putting the holes in a fractal pattern give much better results than holes in more 'normal' pattern. The rest is Calculus explaining how they can generate patterns that are really good at transmitting a certain frequency.

Sounds really interesting. I wonder if any of this applies to antenna design at average RF.

Re:Geek into English.

[Anonymous Coward]

This is trivial. At Starfleet Academy, surface plasmon polaritons and Fano interference in quasicrystals were on our freshman exams in the first week. Even WESLEY got it right, and he was the dumbest one in our class. Well, except for that guy, George Bush VIII. I don't know how he got in, except his father was like the king of some country named Texas or something. All he ever did was exotic drugs, until the day he blew his testicles off in chem lab. Thank goodness for modern transplant technology.

Re:Geek into English.

[mdsolar]

In a way this is a pretty standard result. One can reduce the ringing in a Fourrier transform by including non-periodic sampling. What is provacative is the implication that there is some flaw in the surface plasmon interpretaion. Namely, they point to straight interference as being important rather than the constrained response of the surface electons.
--
Get solar: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html

Re:Geek into English.

[cats-paw]

"Sounds really interesting. I wonder if any of this applies to antenna design at average RF."

yes it does.

Fractal antenna design is old news at this point.

You get a modest reduction in antenna design, but it really excels at giving you a broadband design. So it's particularly handy for UWB.

Re:Geek into English.

[Ungrounded Lightning]

mmmm.. quantum mechanics..

Perhaps more like "maybe a classical explanation is enough, assuming quantum-mechanical approaches are necessary make you miss some useful stuff and work too hard at it".

Or as "classical" as you can get with electromagnetism anyhow...

Re:Geek into English.

[owlstead]

You shouldn't file this under "Geek to English" though.

ridiculously expensive

[evwah]

I regularly work with equipment that produces signals up to 50 GHz and let me tell you... components get much higher in cost the higher in frequency they go. a 3 foot 40GHz cable can cost hundreds of dollars and a 100GHz connector can cost a thousand dollars or more on its own. I imagine that producing and transmitting signals in the terahertz range is not economically viable for most companies.

Re:ridiculously expensive

[markov_chain]

Pshaw, that's nothing. I work with high end audio equipment, and let me tell you, a Hi-Fi 3 foot cable can easily cost several thousand dollars. The 40GHz cable would never be enough, as some people can still hear frequencies in that range.

Re:ridiculously expensive

[Harmonious Botch]

As I recall, people's hearing tops out at about 25 KILOhertz

Re:ridiculously expensive

[John Miles]

I regularly work with equipment that produces signals up to 50 GHz and let me tell you... components get much higher in cost the higher in frequency they go.

Depends on how precise you want to be. Conducting and measuring signals in that region of the spectrum with low-loss gear can be tough. Generating and receiving them isn't, necessarily. Not many people realize that some of the very first wireless communications experiments were done in the 60 GHz range, two years before Marconi.

Re:ridiculously expensive

[Anonymous Coward]

Terahertz signals can be generated using microwave vacuum tubes (BWOs and Gyrotrons) and transmitted through waveguides, so cables aren't really necessary. Reception might be more of an issue, although that's not something I know much about. There is or at least has been work on terahertz generation at the University of Utah as well.

Re:ridiculously expensive

[spiracle]

mod parent -1 "no sense of humor"

Re:ridiculously expensive

[sr180]

I see that his joke was above your head by 39.975 MHz or so.

Re:ridiculously expensive

[cyphercell]

Precision is key for distance, this stuff already doesn't carry that far.

Re:ridiculously expensive

[YU Nicks NE Way]

Since TFA is all about work done on metamaterial filters for terahertz radiation done at the University of Utah, I think you can probably assume that there's still work going on there.

Re:ridiculously expensive

[cyphercell]

At the same time won't the cost of lower frequency hardware go down a little bit with a new premium around?

Re:ridiculously expensive

[truckaxle]

That audible wroooshing sound you hear is the joke going over your head :)

Re:ridiculously expensive

[John Miles]

Not to mention the regulatory hurdles associated with spark gaps...

Re:ridiculously expensive

[cyphercell]

I'm not that smart, just a little familiar with 802.16. Are you saying that the cost of common electronics would need to go up in order to support this?

Re:ridiculously expensive

[Profane MuthaFucka]

Are you talking about compact discs? because you can hear vinyl way higher than that.

Re:ridiculously expensive

[simm1701]

Most people use their Hi-Fi to listen to music

Audiophiles use their music to listen to their stereo :)

Re:ridiculously expensive

[fahrbot-bot]

...a 3 foot 40GHz cable can cost hundreds of dollars and a 100GHz connector can cost a thousand dollars or more on its own...

So, CAT-5e is out?

Re:ridiculously expensive

[cyphercell]

Well I'm glad I just said I was stupid instead of reading that, I might have said something dumber. My land-line wireless phone operates in the 2.4Ghz range, costs about $35 and I can't cross the street with it. That hardly compares with the four mile NLOS you can get these days. No offense but price still seems relevant to me.

Re:ridiculously expensive

[cyphercell]

Nevermind

I get it now it's the connectors not the length of the cable that matters.

Re:ridiculously expensive

[Erandir]

I dunno, apparently many companies are already broadcasting in the 450-750 terahertz range, using something called a "light bulb"...

Re:ridiculously expensive

[91degrees]

A TV remote uses Terahertz frequencies. The components you need depend on what you're using it for.

Re:ridiculously expensive

[Creepy Crawler]

But that varies its frequency upon temperature constant. There's no other way to modulate other than flashes.

Re:ridiculously expensive

[91degrees]

It's just an extreme example of how you can use extremely high frequencies cheeply. Obviously they're not particularly useful at this price, but it's cheap...

Re:ridiculously expensive

[tengwar]

Just RTFA'd - that's definitely Real Physics. I'm impressed.

Re:ridiculously expensive

[EricTheO]

You know when I put a Cd on my turntable it has no hiss, pops, crackle, clicks, or rumble.

Re:Hmm,

[evwah]

micrwave frequencies are usually considered to be the upper end of the radio frequency spectrum... the former being about 1G-300GHz, and the later covering 3Hz-300GHz.

Re:The name for this part of the band.

[evwah]

http://en.wikipedia.org/wiki/Terahertz_radiation

the microwave spectrum is usually considered to end at about 300GHz.

Re:Hmm,

[NixieBunny]

The microwave spectrum really ends at about 30 GHz, with the frequencies from 30G-300GHz called millimeter wave, and those from 300 GHz up called submillimeter. Terahertz technology is quite in its infancy. There was a terahertz conference last week, so the office I work in was pretty well cleared out. (I work on spectrometers that use what we consider low frequencies, The other thing about terahertz waves is that they behave quasi-optically, being focused by teflon lenses and blocked by cardboard. So it's not a radio band that one would use for cellphones.

Not strictly true

[femto]

... a prerequisite for using it for data

It's not strictly true that you need to have bandpass filters to transmit information. There are other ways to select individual users without frequency division multiplexing. For example:

• Do it in the time domain (ultra wideband) using narrow pulses. Each user transmits at a different time.
• Use a spreading sequence to spread the signal so it takes up the entire band, with no need for a narrow filter (CDMA). Each user has a different sequence.
• Use multiple antennas to do space encoding. Users are separated in space, not frequency.

The gotcha is that you need some way of sampling the band. One way is to to use a bandpass filter, mixer and slow sampler. Another is to directly sample (using RTDs???) or in the case of UWB just detect pulses. Bandpass filters are the conventional way of doing it, but not the only way.

Re:Not strictly true

[NixieBunny]

Bandpass filters are not typically used with the astronomical receivers I'm familiar with. They use a local oscillator operating a few gigahertz above or below the interesting signal and just mix it down to microwave. The usual receiver sees the imagefrequency as well as the desired frequency, but the latest generation uses a sideband-separating mixer with hybrid couplers at RF and IF ports to allow separate reception of upper and lower sidebands. The group I work in was the first to apply such receivers to actual astronomical use.

Re:Not strictly true

[femto]

True. My bad. I was forgetting that the filter in front of the mixer isn't so much to eliminate images due to negative frequencies (when using a complex mixer with I and Q components) as to suppress out-of-band signals that might cause overloading, the non-linearity resulting in yet more images. Make the mixer linear enough and you can mix straight down then filter and sample.

Re:Not strictly true

[ChrisA90278]

You are exactly right. All we have to do is look at the very early days of radio, before the invention of the vacuum tube. They used spark gap transmitters that splattered over the entire RF spectrum. If worked just fine when you could count the number of transmitters in range with the thumbs on one hand.

Re:Hmm,

[Pink Tinkletini]

...)

Ahhh, much better.

Too slow

[iminplaya]

I want gamma ray wireless.

Re:Hmm,

[Kenshin]

The other thing about terahertz waves is that they behave quasi-optically, being focused by teflon lenses and blocked by cardboard.

So we can finally ditch the tin-foil hats for cardboard hats? About time!

Re:Hmm,

[cyphercell]

How about "infrared waves", "red shifted microwaves", or the most marketable "redwave wireless".

Re:Hmm,

[NixieBunny]

Cardboard's fine. Just don't assume that your styrofoam hat will block the goverment's secret terahertz ray. Where I work, they use styrofoam for dewar windows!

Re:Hmm,

[cyphercell]

thanks, I would still prefer "bluewave wireless" actually I think that sounds better than "redwave".

Re:What's the point?

[cyphercell]

Space maybe? (thanks I was wondering about the LOS issue)

Re:Hmm,

[flyingfsck]

Is 'RiFi' trademarked yet?

Re:Optical...

[Short Circuit]

Once you get close to the frequency of infrared light... Why not just make the jump, and go with light instead? Perhaps because there aren't many known ways to tune the frequency of visible-spectrum EM emissions at rates which make using that part of the spectrum in that manner effective?

Terahertz research would seem to me to be a step in that direction, by bringing existing EM modulation techniques closer to that spectrum.

And, in the end, we're not going to want to stop there. We're going to eventually want to extend application of understood techniques to the UV bands and beyond.

It may not be effective for communicating in atmosphere, but it'll eventually be a great high-bandwidth solution for intercraft and interplanetary communications. The smaller you can make the parabolic dish, the easier it becomes to effectively focus the signal.

Nikola Tesla springs to mind

[mrbluze]

Didn't Nikola Tesla study/invent devices which work in this frequency spectrum?

I know that not all of his inventions were made public and that much of his writing was confiscated upon his death, but does anyone have any leads on this?

Re:Nikola Tesla springs to mind

[Frank T. Lofaro Jr.]

He is the father of longitudinal and scalar waves, anomalous power generation and quite a few innovations that are still ahead of OUR time.

Re:Optical...

[evilviper]

Perhaps because there aren't many known ways to tune the frequency of visible-spectrum EM emissions at rates which make using that part of the spectrum in that manner effective?

I'm not sure what point you're trying to make here. "Tuning" is absolutely not necessary. Simple off/on digital communications work at very high speeds with fiber optics in the visible light spectrum right now.

Re:Why not...

[Greylin]

oh no.. not petahertz... then we'll have those animal rights crazies demanding we let it go..

Re:The name for this part of the band.

[cyphercell]

It seems to me after looking around here a little bit we ought to start calling it "quantum wireless" to go with that "quantum computer" we always hear about. Not trolling, it's just the summary I get goes like this: Good for LANs, very little penetration (i.e. LOS = bad for indoors), it will suffer dearly at the hands of electromagnetic interference (again cannot survive in the house) and it will be very expensive.

Re:Optical...

[Max Littlemore]

Once you get close to the frequency of infrared light... Why not just make the jump, and go with light instead?

Ummmm. In case you didn't know, people have been using light for years. Ever heard of semaphore?

Re:Optical...

[Short Circuit]

Simple on/off signaling is a very low grade form of amplitude modulation, and thus places limitations on the kinds and rate of signaling you can do without bleeding into neighboring frequencies.

Modulation using FM or QAM allows one to pack a lot more data into a much smaller frequency band, but they require the ability to alter the frequency of the EM radiation.

Re:Hmm,

[cyphercell]

Actually, screw names, I'm going to the patent office!

Patents!!!

P.S. - Mod me insightful.

Re:Optical...

[Mad Bad Rabbit]

Once you get close to the frequency of infrared light... Why not just make the jump, and go with light instead? They're both going to be line-of-sight anyhow, with anything that blocks light very likely also blocks THz rf.

Actually no; terahertz rays can go through wood, sheetrock, masonry, etc. (but not metal or water).

Re:Optical...

[evilviper]

I don't believe frequency overlap is much of an issue with short-distance/line-of-sight (wireless) communications to begin with. It would have to be a very dense open space for many devices to be competing for spectrum.

Re:Optical...

[evilviper]

High-speed digital communications bear little resemblance with low-speed manual signaling.

That said, I'm not sure why you got a Flamebait mod.

Re:Optical...

[Short Circuit]

What with the trend to add information capabilities to anything and everything, I wouldn't be surprised if, in 30 years, we had wireless networks insanely dense by today's standards.

Another thing...Digital amplitude modulation works fine for fiber because fiber has a very high signal-to-noise ratio as a medium, leading to high data integrity. Open does not. FM and QAM offer some protection against this. Listen to the radio during a thunderstorm. Switch between AM and FM, and listen to the noise on each. The AM stations are much noisier than the FM stations, which only click and pop during major bolts. The AM stations, on the other hand, pick up every bit of cloud-to-cloud static discharge.

Re:Optical...

[Max Littlemore]

That said, I'm not sure why you got a Flamebait mod.

Probably because there are no "-1 I don't get it" or "-1 That joke was really lame" options.

Re:Optical...

[cyphercell]

Some controversy surrounds the use of terahertz scanners for routine security checks due to the potential capability to produce detailed images of a subject's body through clothing. X-ray vision

That's what I'm waiting for :)

Re:Hmm,

[grcumb]

Is 'RiFi' trademarked yet?

Somehow I don't think it would work in Japan or China.... Besides, you're missing the obvious one:

TERA-fi, dude!

Re:Hmm

[cyphercell]

Could be because they're both quasicrystals.

It seems to be speculation

[kocsonya]

The New Scientist article is talking about comms, but the Nature abstract actually doesn't have a single word in it with that regards. It only talks about completely different uses. From the abstract:

"Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission."

No comms there at all.

Re:Hmm,

[Whiteox]

Wax is the way to go!
It blocks everything! But don't go out in the hot sun.....

Clueless....

[j_square]

Another example of how the tabloids (Nature & Science) publish things that have been known for ages... There seems to be a trend that you can get anything published there, since the peer review is done by totally clueless physicists who do not know anything about the state of the art.

The concept of making filters by cutting holes in a sheet of metal has been known for ages. Using periodic (or in this case quasiperiodic) metallic patterns is called Frequency Selective Surfaces (FSS). There are numerous books and tons of publications in IEEE transactions, etc. in this area.

I did etched FSS filters for 375 GHz around 1982, and the concept was already pubslished in books by then.

Old stuff. Too many scientists, too much money, too little brain.

Putting SETI out of business

[Ace905]

Watch them put together their first prototype crystal radio with their new 'filter' and find an entire cosmos of alien phone calls, television broadcasts and quasar's giving off travel-instructions to nearby ships.

Some people here have said, this is very old news and the article is the equivalent of saying, 'one day railroad lines will cover this great country of ours' -- but seriously, how many average people - like myself, are aware that we're still not using the full EM spectrum available to us. I thought we conquered radio waves in the 50s and everything since then has just been 'computing speed'. I think this is pretty interesting.

It will be cool to see what new forms of cancer and mental disease equipment broadcasting in this spectrum doesn't cause.

---
WRONG frequency!

Re:Hmm,

[pipatron]

Let's improve that even further!

TERA-fi(c)

Like, terrific traffic!

Re:Coming next...

[flydpnkrtn]

Yea great job on the informative side of that post there guy...

For those that don't know about it (I didn't know about it until a couple of weeks ago:
"Free Space Optics (FSO) is a line-of-sight wireless technology, which enables secure, high speed bandwidth connections using optical laser communication"

http://en.wikipedia.org/wiki/Free-space_optical_co mmunication

I prefer THz for scanning!

[Freqfreq]

... been doin' teraherz for years - it's just "in fashion" now.

Publication with some terahertz images of concealed weapons on people (towards the article end):

http://stl.uml.edu/PubLib/DickinsonDSS2006.pdf

lots of other THz articles if you chop back the URL to PubLib/

Very silly article, once again

[Ancient_Hacker]

I helps if one looks at these things with a certain perspective.

• First, is there a problem that needs solving? Are we really that short of spectrum?
• Secondly, if this is so great, why hasnt it been done already?
• Next, did anybody do a literature search to see if it has been done?
• Next, is this the most economical way to do this?

Otherwise, we end up with wildly expensive proposed solutions using already tried and rejected technology that violates basic laws of physics, scale, or economics, to attack a non-problem. Again.

Re:Very silly article, once again

[zCyl]

* First, is there a problem that needs solving? Are we really that short of spectrum?

Yes there is, and yes we could always use more. First, terahertz communication has a much higher theoretical bandwidth than gigahertz communication. Second, it's not currently locked down by regulation and existing use. (2.45 GHz isn't used for wireless because it's ideal. In fact, it's a wavelength quite likely to absorbed by biological tissue. It's used because regulations permit that band to be used.)

* Secondly, if this is so great, why hasnt it been done already?

Because the electronic components at that timescale are difficult to build. Ever see a terahertz cpu?

* Next, did anybody do a literature search to see if it has been done?

See for yourself. In a very light perusal through titles, essentially every article says "towards" or "future".

* Next, is this the most economical way to do this?

Probably not, but you have to start somewhere before you can get cheaper.

I have a working system already in that range!

[CFD339]

At about 430 terahertz with direct line of sight over a distance of over a mile in some cases. Much longer if you're transmitting through a vacuum.

It can be very fast, but you can build your own slower version simply.

1. Take a red flashlight.
2. Stand on a hill.
3. Have a neighbor stand on another hill.
4. shine light at neighbor.
5. Cover the light with your hand, which produces a bitwise "0"
6. Uncover the light, which produces a bitwise "1"
7. Repeat, encoding your signal in binary at whatever rate your friend can accurately clock.

You may want to consider a "return to zero" phase or a "return to zero inverted" phase (NRZ/NRZI) to help you clock the signal for repeated bits at less accurate clock rates. :-)

Re:I have a working system already in that range!

[inviolet]

At about 430 terahertz with direct line of sight over a distance of over a mile in some cases. Much longer if you're transmitting through a vacuum.

How does anyone know this to be true? IIRC the only vacuum that is larger than a mile is MegaMaid, and AFAIK we don't have access to her.

Awesome technology.

[qazxswedc]

So now your wireless network can take voyeur porn for you... http://en.wikipedia.org/wiki/Terahertz_imaging#The oretical_and_technological_uses_under_development/

Re:Why not...

[iago-vL]

Why make billions when we can make.... millions?

It's not a bug, it's a feature

[Beryllium Sphere(tm)]

High rates of atmospheric absorption mean that Mother Nature is making your network cellular for you. This would be great technology for meshes, because the node three hops away simply can't interfere with you. Sub-mile ranges are also entirely useful for point-to-point links in dense areas. If you had a meeting in Bangkok with someone a mile away, you'd really prefer a broadband video conference over driving a mile in Bangkok traffic.

The physics of radio waves constrain their use

[ChrisA90278]

Some very basics....

An 100 watt HF transmitter (HF is from 3.0 to 30.0 Mhz) has world wide range. You can send a signal all the way around the world at those frequencies becaue the ionosphere bounds the waves back to Earth and the Earth bounces them back up. These HF waves will travel trough things like walls, trees and people.

On the other hand a 100 watt light bulb radiates the same power but it's waves go only in a stight line and can be stopped by a piece of cardboard.

It turns out the wave with frequency between HF and light have properties between HF and light. For example VHF and UHF (used for over the air TV, fire and police radios and so on) these waves travel in a mostly straight line but can be bend somewhat, some times.

Once you get to microwaves they act even more like light. They need a line of sight and are easy to block.

These terraherz waves would act even more like light then microwaves. They are almost infrared and so act almost like infrared So even if you could build it this would be useless for many applications. Possibly it would open up NEW applications such as extreme high speed communications between objects that are almost touching each other but not wifi that covers an area or goes through solid objects.

Re:The physics of radio waves constrain their use

[starbuck5250]

> Once you get to microwaves they act even more
> like light. They need a line of sight and are
> easy to block.

High microwaves, maybe. Amateur radio contesters have been using troposcatter for long haul contacts for decades at frequencies up to 24GHz. For an explanation of troposcatter: http://www.qsl.net/oz1rh/troposcatter99/troposcatt er99.htm Some communications records held by hams: http://www.nzart.org.nz/nzart/vhf/world_dx_records 2006.html

The point isn't to pick a nit, only to note that there are reliable mechanisms that can be used for reliable long haul communications at microwave frequencies. I'm not personally familiar with the attenuation of the atmosphere at 1THz and up; perhaps if we generate 100 watts at 1THz we can use tropo there too...

Re:The name for this part of the band.

[mdsolar]

For those of us who actually use it we say submillimeter and far infrared but as the interest grows in space communications THz is coming more into use. I've seen it used for the mid-infrared as well. Presumably some funding agency started saying THz and lots of people followed. The company is welcome. One far infrared astronomer famously said "These is no such thing as a far infrared detector." This is about right since the properties of the materials we use are really atrocious. History dependent sensitivity, unpredictable dark current, weird spectral response, and internal fringing are just some of the difficulties encountered. Yet, much of the luminosity of the local universe is emitted in this band and many of the most important spectral features of the young universe are redshifted into this band. Improved THz technology is needed and this article is certainly getting noticed in the astronomical community.
--
Intercept the daily optical to terahertz conversion: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html

What about gravity communication?

[heroine]

Forget about terrahertz carriers. I want communication at the frequency of gravity.

Re:What about gravity communication?

[maxwell demon]

Forget about terrahertz carriers. I want communication at the frequency of gravity. Let's see ... I guess the biggest source of gravitational waves in the solar system is Mercury (the planet) on its way around the sun. It circulates the sun once in 88 days, which means the frequency is about 0.13 microhertz. I don't think you get much bandwidth at that frequency :-)

BTW, it's terahertz (from greek teras, monster), not terrahertz (it has nothing to do with the earth).

Re:Optical...

[ChrisMaple]

"tune the frequency of visible-spectrum EM emissions"

Diffraction gratings.

Glass prisms.

Dichroic filters and dichroic mirrors.

Conventional filters based on the optical properties of various chemicals.