'Slow Light' Demonstrated in Optical Fiber

Daniel S. Burgess

A collaboration of researchers from Cornell University in Ithaca, N.Y., the University of Rochester in New York and Duke University in Durham, N.C., has produced optical delays as long as 20 ns -- up to 1.3 times the pulse duration -- in conventional single-mode fiber at room temperature. The "slow light" effect induces delays at telecommunications wavelengths, suggesting potential applications in optical delay lines, buffers and equalizers.

Based on stimulated Brillouin scattering, the technique produces controllable changes in the group velocity of optical pulses in the solid-state medium by inducing variations in its refractive index. In the scientists' experiments, they injected CW radiation from a tunable laser, amplified in erbium-doped fiber, into a 1-km length of Corning SMF-28e fiber, which acted as a Brillouin oscillator and yielded a Stokes signal that they converted into pulses with a modulator and amplified in another, 500-m length of the fiber.

Comparison with unamplified pulses revealed that signal pulses as short as 16 ns were delayed by more than a pulse length, with the magnitude of the delay linearly dependent on the power of the pump field.

By using stimulated Raman scattering, the researchers expect that similar relative delays can be generated at current telecommunications bit rates.

The team reported its work at the Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference in Baltimore in May.