An optical waveguide structure according to the invention comprises a core layer having a first refractive index n_core, an array of sub-regions within the core having a second refractive index n_rods, 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 n_cladding, wherein: n_coren_rods[[]]n_cladding and n_core-n_rods0.1. The structure of the present invention is less lossy than prior waveguide structures having photonic band structure regions. The out of plane divergence of light in the sub-regions is reduced as compared with air holes which are typically used in photonic crystal structures. As a result more light is coupled back into the core at the sub-region/core interface. Coupling of light into the buffer layer is also reduced. Furthermore, there are added advantages over the prior art associated with the fabrication of these structures.