Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

samedi 21 février 2004

Recently, researchers have "stopped light" by storing light pulses in hot or extremely cold gases (check these former stories on Slashdot or at BBC News Online). Now, scientists from Stanford University have devised a method to store light pulses under ordinary conditions. In Light-storing chip charted, Technology Research News says this opens the way for all-optical communications switches, quantum computers and quantum communications devices.

Researchers at Stanford University have come up with a scheme to store light pulses under ordinary conditions using photonic crystal -- semiconductor chips that contain regularly spaced holes or rods of a different material. "Our discovery enables quantum coherent storage of light pulses on a microchip about the size of the grain of salt," said Mehmet Fatih Yanik, a research assistant at Stanford University.
The method would allow light pulses to be stored in microchips at room temperature without requiring any special light-matter interactions, Yanik said.

What's so new in this method?

The key to the researchers' method is a technique that allows them to change -- on-the-fly -- the way portions of the photonic crystal respond to light. "We discovered a practical way to compress light's bandwidth by an unlimited amount... using conventional optoelectronics technologies at speeds sufficient to prevent light pulses [from] passing through our system," said Yanik.
The researchers' simulation shows that light pulses can be slowed to less than 10 centimeters per second, slow enough that the pulses would be held essentially in place for tiny fractions of a second, according to Yanik. This is long enough to make pulses interact to switch light signals for high-speed communications or link photons for quantum computing.
The researchers' light-controlling chip design calls for photonic crystal that contains a series of optical resonators, or cavities. Photonic crystal refracts, or bends, light -- the same effect that produces the familiar bent-drinking-straw illusion. The boundaries made by photonic crystal's holes or rods refract light, and the spacing of these gaps determines the degree to which a given wavelength of light is bent. Photonic crystal can be designed to block or channel specific wavelengths.

Keep in mind that this is only theoretical. The researchers plan to demonstrate this technique by trapping microwave signals within a year. They think that a prototype which works at optical frequencies could be made in two to five years.

The research work should appear soon in Physical Review Letters. But you can already read the abstract of the paper, "Stopping Light All-Optically."

We show that light pulses can be stopped and stored all-optically, with a process that involves an adiabatic and reversible pulse bandwidth compression occurring entirely in the optical domain. Such a process overcomes the fundamental bandwidth-delay constraint in optics, and can generate arbitrarily small group velocities for light pulses with a given bandwidth, without the use of any coherent or resonant light-matter interactions. We exhibit this process in optical resonator systems, where the pulse bandwidth compression is accomplished only by small refractive index modulations performed at moderate speeds.

And if you like mathematical formulas, you also can read the full version (PDF format, 18 pages, 251 KB).

Sources: Eric Smalley, Technology Research News, February 11/18, 2004; and various websites

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