When a light pulse propagates through a transparent, linear, and anomalously dispersive medium, its group velocity can exceed c,
or even become negative. We review recent experiments on superluminal and negative group velocity in various physical systems. We further study the velocity of signal transmission in these situations by closely analyze the optical signal-to-noise ratio. We show that quantum fluctuations limit the signal velocity to values less than c.
©Copyright 1999 KSU Department of Physics