To investigate the physical meaning of pulse peak in fast and slow light media, we investigated propagation of differently shaped pulses experimentally, controlling the sharpness of the pulse peak. Symmetric behavior with respect to fast and slow light was observed in traditional Gaussian pulses; that is, propagated pulses were advanced or delayed, respectively, whereas the pulse shape remained unchanged. This symmetry broke down when the pulse peak was sharpened; in the fast light medium, the sharp pulse peak propagated with luminal velocity, and the transmitted pulse deformed into a characteristic asymmetric profile. In contrast, in the slow light medium, a time-delayed smooth peak appeared with a bending point at $t=0$ . This symmetry breaking with respect to fast and slow light is a universal characteristic of pulse propagation in causal dispersive systems. The sharp pulse peak can be recognized as a bending nonanalytical point and may be capable of transferring information.To investigate the physical meaning of pulse peak in fast and slow light media, we investigated propagation of differently shaped pulses experimentally, controlling the sharpness of the pulse peak. Symmetric behavior with respect to fast and slow light was observed in traditional Gaussian pulses; that is, propagated pulses were advanced or delayed, respectively, whereas the pulse shape remained unchanged. This symmetry broke down when the pulse peak was sharpened; in the fast light medium, the sharp pulse peak propagated with luminal velocity, and the transmitted pulse deformed into a characteristic asymmetric profile. In contrast, in the slow light medium, a time-delayed smooth peak appeared with a bending point at $t=0$. This symmetry breaking with respect to fast and slow light is a universal characteristic of pulse propagation in causal dispersive systems. The sharp pulse peak can be recognized as a bending nonanalytical point and may be capable of transferring information.

Physical Review ADec 23, 20152 citations

The speed of information in a ‘fast-light’ optical medium

Michael D. Stenner, Daniel J. Gauthier, Mark Allen Neifeld

NatureOct 1, 2003356 citations

Fast Causal Information Transmission in a Medium With a Slow Group Velocity

Michael D. Stenner, Daniel J. Gauthier, Mark Allen Neifeld

It is widely believed that the velocity of information ${\ensuremath{\upsilon}}_{i}$ encoded on an optical pulse is equal to the group velocity ${\ensuremath{\upsilon}}_{g}$, at least when ${\ensuremath{\upsilon}}_{g}$ is less than the speed of light in vacuum $c$ . On the other hand, several authors suggest that ${\ensuremath{\upsilon}}_{i}=c$, although the size of the signal traveling at this velocity may be small, thereby making it difficult to measure. Here, we measure ${\ensuremath{\upsilon}}_{i}$ for pulses propagating through a resonant ``slow-light'' medium where ${\ensuremath{\upsilon}}_{g}\ensuremath{\approx}0.006c$. We find ${\ensuremath{\upsilon}}_{i}=1.03{c}_{\ensuremath{-}0.25c}^{+0.49c}$, or that ${\ensuremath{\upsilon}}_{i}\ensuremath{\approx}168{\ensuremath{\upsilon}}_{g}$, clearly demonstrating that the speed of information cannot be generally described by ${\ensuremath{\upsilon}}_{g}$, but is characterized by its own velocity.It is widely believed that the velocity of information ${\ensuremath{\upsilon}}_{i}$ encoded on an optical pulse is equal to the group velocity ${\ensuremath{\upsilon}}_{g}$, at least when ${\ensuremath{\upsilon}}_{g}$ is less than the speed of light in vacuum $c$. On the other hand, several authors suggest that ${\ensuremath{\upsilon}}_{i}=c$, although the size of the signal traveling at this velocity may be small, thereby making it difficult to measure. Here, we measure ${\ensuremath{\upsilon}}_{i}$ for pulses propagating through a resonant ``slow-light'' medium where ${\ensuremath{\upsilon}}_{g}\ensuremath{\approx}0.006c$. We find ${\ensuremath{\upsilon}}_{i}=1.03{c}_{\ensuremath{-}0.25c}^{+0.49c}$, or that ${\ensuremath{\upsilon}}_{i}\ensuremath{\approx}168{\ensuremath{\upsilon}}_{g}$, clearly demonstrating that the speed of information cannot be generally described by ${\ensuremath{\upsilon}}_{g}$, but is characterized by its own velocity.

Physical Review LettersFeb 9, 200564 citations

Information Speed in Controllable Light Velocity

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

Laser & Optoelectronics ProgressJan 1, 20110 citations

t=0

. This symmetry breaking with respect to fast and slow light is a universal characteristic of pulse propagation in causal dispersive systems. The sharp pulse peak can be recognized as a bending nonanalytical point and may be capable of transferring information.

c

. On the other hand, several authors suggest that ${\ensuremath{\upsilon}}_{i}=c$, although the size of the signal traveling at this velocity may be small, thereby making it difficult to measure. Here, we measure ${\ensuremath{\upsilon}}_{i}$ for pulses propagating through a resonant ``slow-light'' medium where ${\ensuremath{\upsilon}}_{g}\ensuremath{\approx}0.006c$. We find ${\ensuremath{\upsilon}}_{i}=1.03{c}_{\ensuremath{-}0.25c}^{+0.49c}$, or that ${\ensuremath{\upsilon}}_{i}\ensuremath{\approx}168{\ensuremath{\upsilon}}_{g}$, clearly demonstrating that the speed of information cannot be generally described by ${\ensuremath{\upsilon}}_{g}$, but is characterized by its own velocity.