High Resolution Imaging of Photonic Crystals

Abstract

The light propagation inside photonic crystals has a strong similarity to the wave propagation of a conducting electron in a crystalline solid. Photonic crystals are structures with a spatial periodically modulated refractive index. The length scale of the modulation is of the same order as the wavelength of light. Given a sufficient index contrast, Bragg like diffraction prohibits certain propagation directions and photon frequency ranges. The localization of light at lattice defects allows one to integrate optic devices on a small scaledue to the sub wavelength scale of the defects. For example line defects may be used to form waveguides and point defects can form frequency selective filters.Regular microscopy images the light that scatters away from some sample. It is limited by diffraction to a resolution of half a wavelength and cannot reveal the detailed patterns of light confinement in photonic crystal defects. In the scope of a diploma thesis, scanning near field optical microscopy has been used on two different photonic crystal types, provided by two collaborating research groups. Images have been taken with sub diffraction limited resolution. The data was used to study the transmission of photonic crystal junctions and to visualize the changing of optical modes in a photonic waveguide as a function of wavelength.