Structure of light in the near field of photonic crystals: -Losses, highly structured intensity patterns and polarization singularities-

Abstract

The huge influence that photonic crystals and plasmonic nanostructures can exert over light at the nanoscale is of both academic and industrial interest. Close to a nanophotonic structure the light field itself becomes highly structured. We have succeeded in measuring the structure of light in the near field of photonic crystal waveguides with phase-sensitive near-field microscopy. It turns out that the evanescent field of these waveguides is much richer than expected due to the Bloch nature of the eigenmodes. For example, it turns out that the light does not decay with a single or even multiple exponent away from the surface as might have naively been expected [1]. With a breakthrough in near-field microscopy we have succeeded to separate the two electric field components in to the plane above the waveguide structure and the phase difference between them. As a consequence we can reconstruct the polarization ellipse for every point above the nanophotonic structure. We find that the polarization above a photonics crystal structure is highly dependent on position to extent that the field even contains polarization singularities [2]. When a nanophotonic structure is used to slow the light down, the concomitant increase in the light-matter interaction leads to a transition at a certain group velocity from a regime where imperfections can be considered as a minor perturbation to one where they come to dominate the light propagation and induce multiple scattering [3].