"Time Telescope" Could Boost Fibre-Optic Communications 183
An anonymous reader writes "A time lens can focus a chunk of time to a point, rather like a normal lens focuses light rays. Put two time lenses together and you can create what a Cornell University team calls a 'time domain telescope' which can magnify time. They sent a 2.5 nanosecond long light pulse, encoding 24 bits of information, into their time telescope. What came out on the other side was the same 24 bit pulse, but compressed into 92 picoseconds. Squashing more information into a light pulse could help to send more information via optical fibres."
Deceptive Name (Score:5, Informative)
I'm used to these physics guys doing all kinds of crazy things with invisibility cloaks and such so I took the title to be a literal time lense.
After RTFA, the "time lense" is a frequency up-shifter. Still impressive, but not supernatural as I had hoped.
Re:Deceptive Name (Score:4, Informative)
After RTFA, the "time lense" is a frequency up-shifter.
So an Auto-Tune, basically.
It's shifting the frequency. (Score:4, Informative)
It's shifting the frequency into a shorter wavelength, without going through a chip.
From the article:
The Cornell team made their time lenses using a silicon waveguide that can channel light. An information-carrying pulse made from a series of
small laser bursts signalling digital 1s and 0s travels through an optical fibre and into the waveguide. As it enters, it is combined with another
laser pulse from an infrared laser. The infrared pulse vibrates the atoms of the waveguide, which in turn shifts the frequencies of the
data-carrying pulse before it exits the waveguide and passes into an optical fibre beyond.
MUX? (Score:4, Informative)
Re:Spacetime, not "squishing time" (Score:4, Informative)
Hrm....
Don't you mean time dilation [wikipedia.org]?
First descibed in 1834 by John Scott Russell (Score:5, Informative)
This is a complete oversell on a normal everyday phenomenon. This is a simple compression of a lightpulse, and has been done for a long time. Dispersion usually smears out a pulse, but can easily, compress the pulse. There is no "bending of time" here. Look up "Chirped pulse amplification" and also "Prism compressor", and maybe "soliton". First descibed in 1834 by John Scott Russell
Re:First descibed in 1834 by John Scott Russell (Score:3, Informative)
No kidding. Its such journalist speak I couldn't figure out what it was talking about.
I think the journalist might have been trying to explain group velocity dispersion aka chromatic dispersion. In a nutshell the speed of light in a vacuum is constant, but in any material it varies a wee tiny bit by frequency, and there is no such thing as a truely monochromatic light source, although we can get pretty close. Work arounds for that problem are VERY OLD NEWS but journalists are always so gullible...
http://en.wikipedia.org/wiki/Chromatic_dispersion#Group_and_phase_velocity [wikipedia.org]
Re:Time compression? (Score:4, Informative)
"Please describe how 'time-compressing' a waveform is different than frequency-shifting it"
If I frequency shift a waveform by a factor of 2, then the time compression is also a factor of 2. The article doesn't really mention it, but the frequency shifts in this experiment are much less than a factor of 2, but the time compression is from 2.5 ns to 95 ps, a factor of 27 compression.
This is a real time lens. A spatial lens works by imparting a quadratic spatial phase to light. Diffraction then causes the beam to focus due to the quadratic spatial phase.
A time lens works in analogy to a spatial lens by imparting a quadratic temporal phase to a light pulse. Propagation in a dispersive media then leads to the time compression.
The difficulty is it is very hard to impart a quadratic phase to short light pulses. The only real way to do it is nonlinear optics, which is where the (small) frequency shifts mentioned in the article come from.
Re:the emperor's new clothes (Score:3, Informative)
If it makes you feel better you can use such sophistry to claim they are the same thing. I'm not clear if you're being intentionally dense or just don't understand.
My point about just calling it "computer networking" is that it certainly is "computer networking". It's also "client server". And it's also "cloud computing". They all add meaning. It's not even that hard to grasp.
I'm using "client server" if I have a few hundred netapps in a computer room and use NFS to expose the data to my client machines. I'm not using cloud computing.
If I use Amazon's storage resources and Amazon's virtual computing infrastructure to host my services then I'm using the cloud.
Of course it's client/server. Almost any system that uses a network could be termed client/server, even e.g. P2P. What's your point?
Re:Time compression? (Score:5, Informative)
Imagine a speech audio signal.
If you were to just compress the signal in time, the rate of speech would increase, but the frequency (pitch) would as well - it would sound like a chipmunk. This is what a simple resampling program would do.
On the other hand if you were to just frequency-shift the signal (say by heterodyning) then the rate of speech would be the same, but the pitch would change. This is what pitch-correction programs do.
If you do both in series and in opposite directions so the cancel, then the pitch remains the same but rate of speech is now increased. This is what fast playback programs (say for audio books) do.
The researchers figured out how to do the last to light using simple lenses. This could be useful because you can send the data down the same channel (like a frequency multiplexed fiber) as the original signal was intended for.
Re:the emperor's new clothes (Score:3, Informative)
It's really the ecosystem of client/server systems provided by many different vendors which together form "the cloud". That's the other part of this - there was originally supposed to be one cloud. Meaning it would be Internet based. Now it's getting diluted and people are applying the same concepts inside a private network.
But again, considering these are networked systems "client server" seems a bit redundant. Like calling client/server "computer networked client/server".
Re:First descibed in 1834 by John Scott Russell (Score:3, Informative)
We're so bad at modulating optical signals that we don't come anywhere near the Shannon limits of the channel. From the sound of it, the 27x increase provided (so far) by this technique also doesn't come anywhere close.
And no, you don't get an article in Nature for regurgitating stuff from old Bell Labs journals.
Re:Time Lens? Not even close. (Score:3, Informative)
Not quite. It's like you driving your 12' long car along the highway. When you drive through a tunnel your car (and you) come out perfect, functional, but only 3' long. After going through another tunnel you regain your original length.
The time lens terminology does seem a little sensational, but it is kind of descriptive. It's also very useful - we're not good at modulating light. We can completely saturate the bandwidth of an RF channel but we can only use a small fraction of the bandwidth of an optical signal. This type of device lets you upsample your slow, crappy modulation into something faster.
Next time you see someone with an article in Nature you might want to take slightly longer to try and figure out what he's actually done before you jump to the conclusion that he's "an #@&*$."