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Scientists Further Optical Data Transmission Research by Slowing Light at Room Temperature

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October 12, 2005 - A team of Berkeley researchers and a researcher from Texas have slowed the speed of light to 245 meters per second at room temperature, further advancing experiments that may some day lead to extremely fast deployment of optical information.

The speed of light in general is not a scientific constant; it is the speed of light in a pure vacuum (the ‘c’ in Einstein’s E=mc2) that cannot be altered. Every material that light can pass through actually has a refractive index, which is a ratio that explains by how much the speed of light is delayed by passing through the material. Slowing light to very low speeds simply involves passing photons, the components of light, through a material with an extremely high refractive index.

Doing so is nothing new. Scientists have been tinkering with "slow light" experiments for over five years, since Danish physicist Lene Hau lead a team of Harvard researches in early 1999 in slowing the speed of light down to 38 miles per hour, or 17 meters per second. Her experiment called for a laser beam to be shone through sodium in a superfluid state, a phase of matter which can exist only in extremely cold temperatures and in an extremely high vacuum. The refractive index of such a state is significant, especially when secondary lasers are added to further control the speed of light.

But the advances in lasers have permitted the Berkeley research team to merely adjust the parameters of the involved lasers themselves, rather than utilize an additional superfluid.

The most significant application for such research would be in eliminating OEO (optical-electronic-optical) conversions. When optical signals are transmitting along fiber optic cables, the signal must be transformed into an electrical one when it reaches a router to avoid a bottleneck, and back into an optical one for superior speed once it has been redirected. This process takes considerable time and power, and circumventing such a switch by slowing the optical signals themselves would make the transmission of optical information much faster—and doing so at room temperature, rather than expensive-to-maintain temperatures of just above absolute zero, would make it much cheaper as well.

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