Superluminal signal conversion in stimulated Brillouin scattering via an   optical fiber ring resonator
  We report the superluminal phenomenon of both Stokes and pump light in stimulated Brillouin scattering (SBS) via an optical-fiber ring lasing resonator. In our experiment, the superluminal generation of Stokes light firstly delayed with 33.79 ns and then propagated with the advancement of 93.34 ns within an 8-m single mode fiber (SMF), when the pump power increased from the SBS threshold to a higher power. This proves the first evidence that the optical interaction is determined by the group velocity even at the negative group velocity superluminal propagation. It is important that, this implies the possibility of superluminal information interchange because the results also indicate that the signal conversion between different wavelengths can be realized at the negative group velocity propagation. 
Liang Zhang, Li Zhan, Jinmei Liu, Gaomeng Wang, Fangying Tao, Taohu   Xu, Qishun Shen
physics.optics