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University physicists break color barrier for sending, receiving photons

Posted: 05 Oct 2010 ?? ?Print Version ?Bookmark and Share

Keywords:physics? fiber optic? data transfer? Internet? security?

University of Oregon scientists have invented a way to change the color of single photons in a fiber optic cable. This laser-tweaked feat could be a quantum step forward in terms of transferring and receiving high volumes of secured data for future generations of the Internet.

The proof-of-concept experiment is reported in a paper about work led by UO physicist Michael G. Raymer which appeared in the Aug. 27 issue of Physical Review Letters.

Meanwhile, in a separate paper also published by the same journal on its Sep. 15 issue, Raymer and co-workers at the University of Bath in the United Kingdom explain how they added hydrogen and a short laser burst to a hollow "photonic crystal" fiber cable to create multiple colors, or wavelengths, of light. Raymer said that this paper offers groundwork for future research in creating ultra-short light pulses.

The single-photon project, in which a dual-color burst of laser light was utilized to alter the color of a separate single photon of light, is directly applicable to future Internet communications technology, stated Raymer, the UO's Knight Professor of Liberal Arts and Sciences, and author of a newly published textbook "The Silicon Web: The Physics Behind the Internet."

In the computing world, digital data now is contained as individual bits represented by many electrons which is then transmitted using pulses of infrared light containing many photons. In quantum computing, a futuristic technology, data might be stored in individual electrons and photons. Such quantum techniques could make data 100 percent secure from hackers and at the same time expand the ability to search large databases, Raymer said.

Raymer further states, "There is a need for more bandwidth, or data rate, in fiber optic networks. In today's fiber optic lines, one frequency of light may carry a phone conversation, while others may carry TV channels or emails, all traveling in separate channels across the Internet. At the level of single photons, we would like to send data in different channels!colors or wavelengths!at the same time. Quantum memories based on electrons emit and absorb visible light!for example, red," he said. "But the optical fibers we want to use!such as those in the ground now!are optimized to transmit infrared, not visible light."

In experiments headed by Raymer's doctoral student Hayden J. McGuinness, researchers used two lasers to deliver an intense burst of dual-color light, which when focused into the same optical fiber carrying a single photon of a distinct color, enabled the photon to change to a new color. This occurs through a process known as "Bragg scattering", wherein a small amount of energy is exchanged between the laser light and the single photon, causing its color to change.

The research was stimulated by work done earlier by Raymer's collaborators: Colin McKinstrie at Alcatel-Lucent Bell Labs and Stojan Radic at the University of California, San Diego.

The second paper published by Raymer's group centers on theoretical and experimental work at UO and at the University of Bath. It showed how to create an optical frequency comb in a hydrogen-filled optical fiber. The optical frequency comb consists of many precisely known colors or wavelengths of light, and can be used to measure the wavelength of light, much as a ruler with many tick marks can be used to measure distance.

The comb method was co-developed by John Hall of the National Institute of Standards and Technology, who won the Nobel Prize in Physics in 2005 for his work that led to the standard for measuring light frequencies.

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