Abstract: 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.

Abstract: In the present invention, an optical device having a waveguide structure includes a photonic band structure region, the photonic band structure region comprising a first region having a first refractive index and an array of sub-regions having a second refractive index, the array of subregions being arranged in a Fibonacci spiral pattern. The present invention can also be applied to optical fibers. The Fibonacci spiral pattern and can be found in nature in the arrangement of the seeds of a sunflower and in pine kernels. The Fibonacci pattern is an optimal packing system for the sub-regions surrounding a central cavity region.

Abstract: 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.

Abstract: An optical waveguide structure according to the invention comprises a core layer having a first refractive index ncore, an array of sub-regions within the core having a second refractive index nrods, the array of sub-regions giving rise to a photonic band structure within the core layer, and a cladding layer adjacent to the core layer having a refractive index ncladding, wherein:

Abstract: In the present invention, an optical device having a waveguide structure includes a photonic band structure region, the photonic band structure region comprising a first region having a first refractive index and an array of sub-regions having a second refractive index, the array of sub-regions being arranged in a Fibonacci spiral pattern. The present invention can also be applied to optical fibres.