'Hexagon-type' photonic crystal slabs based on SOI

In this paper we discuss the design of a novel category of photonic crystal slabs (PCS) and as an example, we consider structures based on SOI wafers. Fabrication issues related to lithographic accuracy are addressed, too. The geometry consists in a triangular lattice of hexagons having their symmetry axes rotated with respect to the lattice.We show that the mirror-symmetric 'hexagon-type' PCS with air claddings can have an absolute (i.e. polarization independent) gap in guided modes with normalized width of approximately 10%. This gap, although reduced to about 4%, is still present in an asymmetric geometry, when the under-cladding is a silicon oxide layer with deeply etched holes.