Observation of polarization singularities at the nanoscale

Diffracted waves are widespread in nature. They can be generated by the scattering with disordered and/or ordered system. Topological defects, such as phase dislocations or polarization singularities, can be hidden in complicated field pattern that arises from this multiple scattering. Photonic crystals owe their peculiar optical properties from the interference that emerges from the diffraction of electromagnetic waves. The question now arises whether topological defects are present in the light in and around the photonic structure. While efforts have been made to study the Bloch-nature of the electromagnetic wave propagating in such a waveguide, much less attention has been given to other aspects of the sub- wavelength structure of the light field. This paper presents results on the sub-wavelength structure of light in the near field of a photonic crystal waveguide. Features that are the fingerprint of topological defects present in the electromagnetic field distribution of photonic nanostructures are observed using a phase-sensitive near-field microscope. Polarization singularities that are present in a single unit cell of a photonic crystal waveguide are also observed.