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"Time Telescope" Could Boost Fibre-Optic Communications
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."
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.
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.
The abstract of the actual article is a little more informative, but still makes strange claims. I think they can compress a 10Ghz electrical signal into a 270GHz optical signal, with obvious ramifications in multiplexing, as you can then take 27 such signals at a time (theoretically).
Hrm....
Don't you mean time dilation?
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-Sigismund, Holy Roman Emperor (1368-1437)
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
don't cut it off www.mgmbill.org
"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.
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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.