Near-field optical investigation of three-dimensional photonic crystals

We show that the coupling of light from an external pointlike light source into a three-dimensional photonic crystal depends on the relative launching position with respect to the crystal lattice as well as on the frequency of light. The results are obtained with a near-field technique which is used to acquire optical information beyond the diffraction limit and to access optical details within the unit cell of the crystal. The experiments are performed at frequencies near the second-order L-gap. As a result, the changes in the shape of the near-field pattern are explained by the photonic properties of the crystal.