Pump it up

More and more of our communications - from text messages to high-definition television - travel over optical fibre.

But there's a problem: Light is dimmed by miles of fibre, and the crisp on-and-off pulses that represent the ones and zeros of a digital signal become misshapen and fuzzy. Every 50 miles or so the signal must be reamplified, cleaned up and relaunched.

Now Cornell University researchers have demonstrated that all this can be done on a single photonic microchip, replacing bulky bundles of fibre or electronic amplifiers.

Previously Alexander Gaeta, professor of applied and engineering physics, and Michal Lipson, associate professor of electrical and computer engineering, had demonstrated a light amplifier on a silicon chip using a process called four-wave mixing, which could amplify an optical signal by "pumping" with another beam of light.

Now, they have shown how that the same process can clean up and sharpen the pulses that travel the length of a fibre-optic cable too. If the pumping beam consists of a series of pulses synchronised with the input signal, the process also cleans up "timing jitter," in which the pulses are not only deformed but also move slightly forward or back in time.