Slow Light in Optical Fibers

Abstract

The group velocity at which light pulses propagate through a dispersive material system is very different from the vacuum speed of light c, One refers to light as being “slow” for vg c or vg <0 (Stenner et al, 2003 ). For vg <0, the pulse envelope appears to travel backward in the material (Gehring et al, 2006), and hence it is sometimes referred to as “backward light.” The subject of slow light has caused keen interest in the past decade or more, and it is possible to control the group velocity of light pulses in the dispersive materials. Interest in slow and fast light dates back to the early days of the 20th century. Sommerfeld and Brillouin (Sommerfeld & Brillouin, 1960) were intrigued by the fact that theory predicts that vg can exceed c, which leads to apparent inconsistencies with Einstein’s special theory of relativity. Experimental investigations of extreme propagation velocities were performed soon after the invention of the laser (Faxvog and et al, 1970). In 1999, Harris’s group research work greatly stimulated researchers’ interests, which showed that light could be slowed down to 17m/s. The result was obtained in ultra cold atom clouds with the use of electromagnetically induced transparency (EIT), which induces transparency in a material while allowing it to retain strong linear and nonlinear optical properties (Hau et al, 1999). Slow light can also be obtained through the use of the optical response of hot atomic vapors (Philips et al, 2001). These early research works require hard conditions and the slow light cannot operate in room temperature. Recently, researchers found ways to realize slow light operating in room temperature and solid-state materials, which are more suited for many practical applications, namely slow light via stimulated Brillouin scattering(SBS), slow light via coherent population oscillations (CPO), tunable time delays based on group velocity dispersion or conversion/ dispersion(C/D), slow light in fiber Bragg gratings and so on. In this chapter, we describe some of the physical mechanisms that can be used to induce slow and fast light effects in room-temperature solids (Bigelow et al, 2003) and some of the exotic propagation effects that can thereby be observed. We also survey some applications of slow and fast light within the fields of quantum electronics and photonics.