Light Manipulation Improved

A special hollow-core photonic crystal fiber has been used to manipulate light a million times more efficiently than ever before.

The research by a team at the University of Bath, England, led by Fetah Benabid said the work has opened the door to what could prove to be a new branch of photonics -- the science of light guidance and trapping. The discovery relates to the emerging field of attotechnology, the ability to send out pulses of light that last only an attosecond, a billion billionth of a second.

These pulses are so brief that they allow researchers to more accurately measure the movement of subatomic particles such as the electron, the tiny negatively-charged entity which moves outside the nucleus of an atom. Attosecond technology may throw light, literally, upon the strange quantum world where such particles have no definite position, only probable locations.

To make attosecond pulses, researchers create a broad spectrum of light from visible wavelengths to x-rays through an inert gas. This normally requires a gigawatt of power, which puts the technique beyond any commercial or industrial use.

But Benabid’s team used a photonic crystal fiber (PCF), the width of a human hair, which traps light and the gas together in an efficient way. Until now, the spectrum produced by PCF has been too narrow for use in attosecond technology. But the team was able to produce a broad spectrum using what is called a Kagomé lattice, using about a millionth of the power used by non-PCF methods.

“This new way of using photonic crystal fiber has meant that the goal of attosecond technology is much closer," said Benabid, of the University of Bath’s Department of Physics, who worked with students Francois Couny and Phil Light and with John Roberts of the Technical University of Denmark and Michael Raymer of the University of Oregon. “The greatly reduced cost and size of producing these phenomenally short and powerful pulses makes exploring matter at an even smaller detail a realistic prospect.”

Benabid’s team has not only made an important step in applied physics, but also has contributed to the theory of photonics. The effectiveness of PCF, so far, as been in its ability to exploit photonic bandgap, which stops photons of light from “existing” in the fiber cladding and enables them to be trapped in the inside core of the fiber.

Instead, the team made use of the fact that light can exist in different "modes" without strongly interacting. This creates a situation in which light can be trapped inside the fiber core without the need of photonic bandgap. Physicists call these modes "bound states within a continuum."

The existence of these bound states between photons was predicted at the beginning of quantum mechanics in the 1930s, but this is the first time it has been noted in reality, and marks a theoretical breakthrough, the researchers said.

The research was published this week in the journal Science.

For more information, visit: www.bath.ac.uk