A STRUCTURE EXHIBITING A PHOTONIC BAND GAP, A METHOD O FORMING THE STRUCTURE, AN OPTICAL SWITCH INCORPORATING THE STRUCTURE, AN OPTICAL DEVICE COMPRISING A BODY HAVING AT LEAST ONE PATH, AN OPTICAL SWITCH, OPTICAL DIODE OR TRANSISTOR INCORPORATING THE OPTICAL DEVICE, AND AN OPTICAL DEVICE HAVING AN OPTICAL TRANSMISSION PATH

摘要

In order to create an optical device with a photonic band gap extending in two dimensions and with very uniform properties in any direction and for any polarisation state, to within 1%, air holes are etched within a substrate of 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, an etched substrate with a regular crystal structure or quasicrystal structure exhibits a non-linear refractive index. Two adjacent areas in such a substrate have different lattice properties, or have defects in the lattices, to create a unidirectional transmission path (diode action). A further beam of light may be used to modulate the transmission path by reason of the non-linear refractive index.