Ultrafast reciprocal space investigation of cavity-waveguide coupling.

Local information on the coupling mechanism between the photonic crystal nanocavity and the feeding waveguide is crucial to enable further improvements of the performance of these systems. Although several investigations on such a coupling have already been performed, information on the local dynamic properties remains hidden. Here, we present a reciprocal space investigation of the dynamics of light side-coupled to a photonic crystal nanocavity. We find that the coupling is promoted by Bloch harmonics having greater transverse momentum.