Fast Light and the Speed of Information Transfer in the Presence of Detector Noise

• Main Authors: Michael Z. Feng, Wayne V. Sorin, Rodney S. Tucker
• Format: Article
• Language: English
• Published: IEEE 2009-01-01
• Series: IEEE Photonics Journal
• Subjects: Fast light; information transfer; pulse advancement; Q-factor
• Online Access: https://ieeexplore.ieee.org/document/5232875/

The phenomenon of fast-light pulse propagation has seen renewed interest in recent years, but its relationship to the <i>speed of information transfer</i> is still being debated. In this paper, we define the <i>speed of information transfer</i> as the propagation speed of a point of constant signal-to-noise ratio (SNR) on the leading edge of a signal pulse. We use standard telecommunication analysis to include the effects of noise so that the bit-error rate (BER) can be calculated as a function of a variable decision time. We introduce the concept of a time-dependent Q-factor so that pulse arrival times can be compared at equivalent BERs. We show that when receiver noise is included in a gain-assisted fast-light system, the measured <i>speed of information transfer</i> can exceed the speed of light for an equivalent pulse travelling through a vacuum.