Scientists Turn Light Into Sound
By turning light waves into slow-moving sound waves, researchers have developed a new method for storing information inside a fiber optic cable.
The technique, demonstrated by scientists at Duke University, is different from other storage methods because it uses the optical fiber itself as the storage medium.
Light waves moving through an optical fiber generate an electric field. When exposed to such an electric field, an optical fiber can change its density - a phenomenon known as "electrostriction."
Information can be encoded in the waveform of an optical fiber. Under the influence of an electric field, the density of the optical fiber changes in correspondence with the peaks and valleys of its waveform. The information encoded in the waveform is then encoded in the densities of the optical fiber, as well.
Density variations are not waves in themselves. But by sending a second light beam through the optical fiber, in addition to the first light beam carrying the information, the scientists could turn the density variations into a slow-moving sound wave with the data encoded in it.
This means that, even after the light waves pass through the optical fiber, the fiber still retains the information encoded in the light waves. The extra storage time is currently quite small - about 10 nanoseconds. But in the fast world of sending light down optical fibers, it could make a difference. The researchers also predict that they can increase the storage time.
To "read" the information temporarily stored in the sound wave, another light pulse is sent down the optical fiber, which reverses the process. The densities in the sound wave, which contain the original data, are transferred onto the light wave as it moves toward its destination.
The new method has several advantages compared with the current method for storing information in optical fibers, which transfers light waves into electric signals and then back again (releasing a great deal of heat in the process). The light-to-sound-wave technique can work at any wavelength and at room temperature, and also uses commercially available, low-cost materials.