'Time telescope' speeds up optical transmission by 27 times
October 4, 2009
Most of today's telecommunication data is encoded at a speed of 10 Gbit/s, but researchers are constantly looking for new ways to push this limit even further. A group of researchers at Cornell University have recently come up with the "time telescope," a sophisticated system that can speed up optical communication by 27 times to an outstanding 270 Gbits/s by squeezing more information into a single flash of light and that, unlike previous solutions, does so in an energy-efficient manner.
Pushing the limit beyond 10 Gbps with today's electronics is proving challenging because engineers have to deal with a series of technological constraints that don't allow it to deliver much higher frequencies.
Faster transmission speeds can be achieved with optical fiber, but this usually requires a lot of energy because photons, which don't interact with each other easily, must be "forced" to do so. The team's work gets around the issue and makes achieving these higher speeds cheaper and much more energy-efficient.
The device developed by the Cornell team is called a "time telescope" and includes two silicon chips called "time lenses" — which work together like the lenses of a normal telescope — lengths of optical fiber and a laser. Because of its small size, it could be used in optical chips inside a computer, as well as for speeding up Internet connections over long distances.
The time telescope achieves these ultra-high speeds by squeezing more information — up to 24 bits — into each burst of light, and it does so by using silicon waveguides that can channel light.
As the information enters the waveguide, it is combined with a laser pulse from a series of infrared lasers that vibrates the atoms of the waveguide. The vibration lowers the frequencies of the front of the light pulse and increases those in its tail, effectively compressing the signal. As a result, the pulse is "squeezed" but no information is lost in the process.
The team then used a second time lens to convert the compressed pulse back into a 24-bit signal, and observed that the pulse duration shrank from 2.5 nanoseconds to 92 picoseconds, speeding up the data rate by over 27 times.
The physics involved are complex, but the net effect is that the system can speed up optical communication significantly, requiring no more energy than that needed to power the lasers, which is significantly less than that required by analogous systems previously developed by other researchers.
The device could be used to compress the data passing through packet-based optical networks, allowing to send 27 times as much information on the same wavelength channel, even though the information would have to be decompressed and then compressed again before and after every router, which would account for a small lag.