Soliton self-frequency blue-shift in gas-filled hollow-core photonic   crystal fibers
  We show theoretically that the photoionization process in a hollow-core photonic crystal fiber filled with a Raman-inactive noble gas leads to a constant acceleration of solitons in the time domain with a continuous shift to higher frequencies, limited only by ionization loss. This phenomenon is opposite to the well-known Raman self-frequency red-shift of solitons in solid-core glass fibers. We also predict the existence of unconventional long-range non-local soliton interactions leading to spectral and temporal soliton clustering. Furthermore, if the core is filled with a Raman-active molecular gas, spectral transformations between red-shifted, blue-shifted and stabilized solitons can take place in the same fiber. 
Mohammed F. Saleh, Wonkeun Chang, Philipp Hoelzer, Alexander Nazarkin,   John C. Travers, Nicolas Y. Joly, Philip St.J. Russ...
physics.optics cond-mat.other nlin.PS physics.plasm-ph