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, K. (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