Slowing the speed of light

Scott Moon, J. Park, Jung Mi Oh +5 more

Previously demonstrated slow light is still far from applications, particularly due to the limited bandwidth and control speed. Although semiconductor-based slow light has the high bandwidth and sub-nanosecond control speed, slow light was observed only in the absorption regime with attenuation, while fast light observed in the gain regime with amplification. The large power difference in two regimes makes the use of the optical delay impractical. We report novel slow light in the gain regime, with a high power comparable to that of fast light, utilizing the anomalous gain characteristic in a gain-clamped semiconductor optical amplifier. The slow light is tunable to fast light with the current as the only variable. Additional high speed operation, fast delay control, and wide range of operation wavelength make the present approach practical.

Lene Vestergaard Hau

Rolf W. Landauer

Joseph E. Vornehm, Robert W. Boyd

In early 1999, a news article in the prestigious journal Nature led off with the announcement, "€œAn experiment with atoms at nanokelvin temperatures has produced the remarkable observation of light pulses traveling at velocities of only 17 m/s."€ The review continued with the understatement, "Observation of light pulses propagating at a speed no faster than a swiftly moving bicycle...comes as a surprise."€ These findings (and their review) marked the beginning of the current wave of interest in the field that has come to be called "€œslow light.â€" When we refer to "the speed of light," we typically mean c, the phase velocity of light in a vacuum, or the speed of propagation of the phase fronts of monochromatic light. The phase fronts travel more slowly through a material, propagating at the speed c/n, where n is the index of refraction of the medium. However, this ordinary slowing of the phase velocity is not slow light. "€œSlow light"€ and "€œfast light"€ refer to changes in the group velocity of light in a medium. A pulse of light can be decomposed mathematically into a group of monochromatic waves at slightly different frequencies, as in Fig. 19.1. In a dispersive material, these monochromatic waves travel at different speeds. When one views the propagation of the pulse as a whole, its apparent velocity depends on the extent of the spread of individual monochromatic-wave velocities. Each monochromatic wave travels at its own phase velocity, while the pulse travels at the group velocity. Of course, the group velocity of a pulse of light is not a new concept. The field of slow and fast light has drawn on theory and developments from the work of Sommerfeld and Brillouin from 1907 to 1914, experiments with early laser amplifiers in 1966, and other work done through the end of the 20th century. (For more of the history behind slow and fast light, see Refs. 8 and 9.)

Ulf Leonhardt, Luciana C. Dávila Romero

The physics of slow-light propagation in atomic Lambda systems is described by the theory of integrable systems, which allows the existence of solitons. Slow-light solitons are stable polarization structures that propagate through the atomic medium at a controllable speed. They represent generalizations of the experimentally demonstrated slow-light pulses in atomic media where one light polarization dominates the other, the probe, and controls its group velocity. In the general case, the overall intensity controls the speed of the entire polarization structure. For zero detuning between light and atoms, even more general shape-preserving pulses exist. Quantum fluctuations of slow-light pulses can be stored in atomic media. In the case of solitons, these are fluctuations of the soliton parameters.