Abstract: A waveguide structure according to the invention comprises a core layer (10), having a refractive index ncore, and an array of rods (11) in the core layer having a refractive index nrods. The refractive indices satisfy the inequality: nrods>ncore. In a planar waveguide structure buffer (12) and cladding (13) layers are included, having a refractive index nbuffer and ncladding respectively. The refractive indices then satisfy the inequality: nrods>ncore>ncladding and nbuffer. This condition provides greater vertical confinement of the E-field of an optical signal passing through the waveguide. Furthermore, it allows waveguides to be formed of a glassy material having a similar refractive index and core dimensions to that of a fiber. A high refractive index contrast within the photonic crystal region is used while totally eliminating the need for mode conversion to launch light in and out of the waveguide.

Abstract: A waveguide structure (200) according to the invention comprises a core layer (210), a cladding layer (206) and a buffer layer (208). Sub-regions (204) are formed in the cladding layer (206) but not in the core layer (210). In one dimensional applications the sub-regions are slots: in two dimensional applications the sub-regions are rods. The rods or slots may be air-filled or filled with an in-fill material, (e.g. Si). The in-fill material, if present, enhances the contrast in dielectric constant between sub-regions (204) and the core layer (210). Sub-regions (204) may furthermore be formed in the portion of the buffer layer neighbouring the core layer. Slots or rods in the buffer may be air-filled or filled by an in-fill material. Substantially complete confinement of the mode in the core can be assured while still maintaining the ability to interact with the field within the photonic band structure region.

Abstract: A waveguide structure according to the invention comprises a core layer (10), having a refractive index ncore, and an array of rods (11) in the core layer having a refractive index nrods.