Micro-cylinder mode in photonic quasicrystal observed by near-field optical microscopy

We propose and realize a micro-cylinder mode in photonic quasicrystal (PQC) on the top of an edge-emitting GaN light emitting diodes (LEDs) with 30 μm indium tin oxides (ITO) covered and 8 μm GaN exposed broad-stripe. A well-defined hexagon-like localized state following a C6v symmetry is identified from the PQC micro-cylinder arrays. Enhancement factor of the surface light extraction from 12-fold PQC patterns on electrical current injected GaN-based light emitters is 2.4 times higher than non-patterned regions, which is observed by scanning near-field optical microscopy (SNOM). According to the near-field optical images, micro-cylinders can be considered as nano-optics sources because the electromagnetic energy is strongly concentrated due to the wave guide modes and the beaming effect of the surface microstructures.