OPTICAL DEVICE

摘要

In order to create an optical device with a photonic band gap extending in t wo dimensions and with very uniform properties in any direction and for any polarisation state, to within 1 %, air holes are etched within a substrate o f low refractive index material such silicon oxynitride or silica glass. The ratio of air hole area to the remainder of the substrate is low, being less than 35 %. The air holes define a quasicrystal structure, having twelve fold symmetry, being based on a square-triangle system. In another development, a n etched substrate with a regular crystal structure or quasicrystal structure exhibits a non-linear refractive index. Two adjacent areas in such a substra te have different lattice properties, or have defects in the lattices, to creat e a unidirectional transmission path (diode action). A further beam of light m ay be used to modulate the transmission path by reason of the non-linear refractive index.