We demonstrate, by theory and experiment, the ultrafast tilting of the dispersion curve of a photoniccrystal 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.

Phys. Rev. Lett.

Beggs, D. M., Krauss, T. F., Kuipers, K., & Kampfrath, T. (2012). Ultrafast tilting of the dispersion of a photonic crystal and adiabatic spectral compression of light pulses. Phys.Rev.Lett., 108(Article number: 33902), 1–5. doi:10.1103/PhysRevLett.108.033902