We show the real-space observation of fast and slow pulses propagating inside a photonic crystal waveguide by time-resolved near-field scanning optical microscopy. Local phase and group velocities of modes are measured. For a specific optical frequency we observe a localized pattern associated with a flat band in the dispersion diagram. During at least 3 ps, movement of this field is hardly discernible: its group velocity would be at most c /1000. The huge trapping times without the use of a cavity reveal new perspectives for dispersion and time control within photonic crystals.

Phys. Rev. Lett.

Gersen, H, Karle, T.J, Engelen, R.J.P, Bogaerts, W, Korterik, J.P, van Hulst, N.F, … Kuipers, L. (2005). Real-Space observation of ultraslow light in photonic crystal waveguides. Phys.Rev.Lett., 94(Article number: 73903), 1–4. doi:10.1103/physrevlett.94.073903