FAYETTEVILLE, Ark. — University of Arkansas physicists have used a newly developed technique that can stop light to create an all-optical switch. This is the first experimental demonstration of efficient all-optical switching in such system with a high degree of control.

Such an all-optical switch has potential applications in the fields of all-optical communications and optical computing, which may be more efficient and use less light energy than traditional methods.

Min Xiao, professor of physics, Hai Wang, a postdoctoral associate, and graduate student David Goorskey reported their findings at a recent Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science meeting in Long Beach, Calif.

To create an efficient optical switch, Xiao used features of "electromagnetically induced transparency" (EIT), a recently discovered process that makes atoms transparent to light they usually absorb. EIT has enabled researchers to slow and stop light, and it also has nonlinear optical properties that Xiao and his colleagues used to create their switch.

EIT media (three- or four-level atomic systems, coupled with multiple laser beams) can create large changes in light energy of one laser beam with small changes in the frequency or light intensity of another laser beam, a desirable effect for any switch.

Xiao and his colleagues used a system with a gas of prepared rubidium atoms inside an optical ring cavity, which uses mirrors to create a ring of laser light. The researchers changed the color or frequency of various lasers, thereby causing coherence or quantum interference in the rubidium atoms. By changing the frequency of a controlling laser beam coupled to one of the atomic transitions, the intensity of the cavity output field-which is coupled to another atomic transition-can be changed by a factor of 30, producing "on" and "off" states. The switch works because of the nonlinear enhancement that creates a large intensity change in the cavity resulting from a small change in the frequency or intensity of the controlling laser beam.

Such all-optical switching requires only weak intensity light and one day may require only a single photon to perform, although this has not yet been demonstrated, Xiao said.

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