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Rainbow Trapping in Light Pulses

Over the past decade, scientists have succeeded in slowing pulses of light down to zero speed by letting separate frequency components of the pulse conspire in such a way that a receptive medium through which the pulse is passing can host the information stored in the pulse but not actually absorb the pulse's energy.

Trapping light means either stopping the light temporally or confining the light in space. Scientists have also been able to trap a light pulse in a tiny enclosure bounded by metamaterials; the light pulse retains its form but is kept from moving away.

Previously only light of a short frequency interval could be trapped in this way. Now a group of scientists at Nanjing University in China have shown how a rather wide spectrum of light -- a rainbow of radiation -- can be trapped in a single structure. They propose to do this by sending the light rays into a self-similar-structured dielectric waveguide (SDW) -- essentially a light pipe with a cladding of many layers. Light of different colors propagates separately in (or is contained within) different layers, the layers each being tailored by color. They replace the conventional periodically-spaced, identical cladding layers with a non-periodic, self-similar pattern of successive layers made from two materials, A and B, with slightly different thicknesses and indices of refraction. Self similarity, in this case, means that the pattern of layers successively outwards would be as follows: A, AB, ABBA, ABBABAAB, and so forth.

"The effect might be applied for on-chip spectroscopy or on-chip 'color-sorters,'" says Ruwen Peng, one of the Nanjing researchers. "It might also be used for photon processing and information transport in optical communications and quantum computing." Peng and her associates, who published their results in the American Institute of Physics' journal Applied Physics Letters, expect that they can create trapped "rainbows" for light in many portions of the electromagnetic spectrum, including microwave, terahertz, infrared, and even visible.

The article "'Rainbow' trapped in a self-similar coaxial optical waveguide" by Qing Hu, Jin-Zhu Zhao, Ru-Wen Peng, Feng Gao, Rui-Li Zhang, and Mu Wang was published online in the journal Applied Physics Letters in April, 2010. See:

Journalists may request a free PDF of this article by contacting

Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, Applied Physics Letters offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. Content is published online daily, collected into weekly online and printed issues (52 issues per year). See:
The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world's largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.

Jason Socrates Bardi | Newswise Science News
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