Researchers at the University of Rochester are detailing a breakthrough in optics that allows them to encode an entire image's worth of data into a photon, slow the image down for storage, and then retrieve the image intact. This development could allow the storage of massive amounts of information in very small spaces.

The article titled “All-Optical Delay of Images using Slow Light,” submitted November 2006, was published today. The abstract reads:

Two-dimensional images carried by optical pulses (2 ns) are delayed by up to 10 ns in a 10 cm cesium vapor cell. By interfering the delayed images with a local oscillator, the transverse phase and amplitude profiles of the images are shown to be preserved. It is further shown that delayed images can be well preserved even at very low light levels, where each pulse contains on average less than one photon.

The image “UR” (for the University of Rochester) was made using a single pulse of light. To produce the UR image, researchers simply shone a beam of light through a stencil with the U and R etched out. This is similar to the way shadow puppets work, but the research team turned down the light so much that only a single photon was all that passed through the stenci).

While the initial test image consists of only a few hundred pixels, the team believes that a tremendous amount of information can be stored with the new technique – as many as a hundred of these pulses can fit at once into a four-inch cell, opening the door to storing information as light. The buffered pulse is essentially a perfect original; there is almost no distortion, no additional diffraction, and the phase and amplitude of the original signal are all preserved.

 “It sort of sounds impossible, but instead of storing just ones and zeros, we're storing an entire image,” says John Howell, assistant professor of physics and leader of the team that created the device. ”It's analogous to the difference between snapping a picture with a single pixel and doing it with a camera—this is like a 6-megapixel camera.”

Howell has so far been able to delay light pulses 100 nanoseconds and compress them to 1 percent of their original length. He is now working toward delaying dozens of pulses for as long as several milliseconds, and as many as 10,000 pulses for up to a nanosecond.

“Now I want to see if we can delay something almost permanently, even at the single photon level,” says Howell. “If we can do that, we're looking at storing incredible amounts of information in just a few photons.”

 “You can have a tremendous amount of information in a pulse of light, but normally if you try to buffer it, you can lose much of that information,” says Ryan Camacho, Howell's graduate student and lead author on the article. “We're showing it's possible to pull out an enormous amount of information with an extremely high signal-to-noise ratio even with very low light levels.”

Storing information as light is a particularly hot field right now because engineers are trying to speed up computer processing and network speeds using light, but their systems bog down when they have to convert light signals to electronic signals to store information, even for a short while.