Patent ID: 7346249

Claim:
An optical waveguide, comprising: a core, comprising an elongate region of relatively low refractive index; a photonic bandgap structure arranged to provide a photonic bandgap over a range of wavelengths of light, the structure, in a transverse cross section of the waveguide, surrounding the core and comprising elongate relatively low refractive index regions interspersed with elongate relatively high refractive index regions; and a relatively high refractive index boundary at the interface between the core and the photonic bandgap structure, the boundary having a thickness around the core such that, in use, light guided by the waveguide is guided in a transverse mode providing an F-factor of less than 0.23 μm −1 for an operating wavelength of 1.55 μm, less than an equivalent F-factor value scaled for a different operating wavelength or less than 0.7Λ −1 for structures having a periodic cladding and a pitch Λ.