Fast light and signal velocity

A. M. Akulshin, Peter Hannaford, Russell McLean +1 more

Makoto Tomita

Zhenshan S. Yang

We study the physical mechanism and the information velocity of fast light based on the time-domain propagator governing light propagation in a dispersive system. We show that the output pulse can be regarded as the superposition of multiple ``copies'' of the input pulse, each traveling at a well-defined signal velocity no greater than the speed of light in vacuum, and the interference between the front edges of these copies generates the peak of the output pulse. The information velocity is defined as the ratio of the propagation distance to the mini-mum time required to complete any given information transfer process, directly reflecting how fast the signal of interest, i.e., the part of the pulse that carries the information of interest, propagates. With the peak of the output pulse representing the information, as is typical in slow- and fast-light applications, we find that the information velocity is significantly smaller than the speed of a discontinuity in the pulse, which was traditionally proposed to be the signal velocity of fast light. The analysis can also be applied to slow-light propagation.

Hao Wang, Chunguang Zhang

Recently, researches about the controllable group velocity of light propagation had made many progresses. And several experiments had demonstrated the signal evolution of slow and fast light. In this letter, the authors described a simple experiment for the tracing of light signals in an erbium-doped optical fiber at the optical communication wavelength firstly. We have, directly, observed the evolution of slow and fast signals with different waveforms that travel in an erbium-doped fiber amplifier. Through tracing the signal evolution, when slow light (Vg<;<;c) or fast light (Vg<;0) was got in it, we concluded that asymmetrical absorption and amplification on the periodical signal could account for the generation of slow and fast light in an erbium-doped fiber amplifier easily.

王号 Wang Hao, 张春光 Zhang Chunguang, 李晖 Li Hui

Francisco Arrieta-Yáñez, Sonia Melle, Óscar G. Calderón +2 more

We propose a technique to obtain slow and fast light propagations based on coherent population oscillations forced by a modulated pump. This mechanism produces an enhancement of 1 order of magnitude of the delay or advancement of light signals. The relative phase between the pumps to the signal fields is used as a knob for changing light propagation from ultraslow group velocities to negative group velocities. The experimental realization of the phenomenon was carried out in an erbium-doped fiber amplifier at room temperature.