Ultrafast tilting of the dispersion of a photonic crystal and adiabatic   spectral compression of light pulses
  We demonstrate, by theory and experiment, the ultrafast tilting of the dispersion curve of a photonic-crystal waveguide following the absorption of a femtosecond pump pulse. By shaping the pump-beam cross section with a nanometric shadow mask, different waveguide eigenmodes acquire different spatial overlap with the perturbing pump, leading to a local flattening of the dispersion by up to 11 %. We find that such partial mode perturbation can be used to adiabatically compress the spectrum of a light pulse traveling through the waveguide. 
Daryl M. Beggs, Thomas F. Krauss, L. Kuipers, Tobias Kampfrath
physics.optics