A waveguide structure according to the invention comprises a core layer (10), having a refractive index n.sub.core, and an array of rods (11) in the core layer having a refractive index n.sub.rods. The refractive indices satisfy the inequality: n.sub.rods>n.sub.core. In a planar waveguide structure buffer (12) and cladding (13) layers are included, having a refractive index n.sub.buffer and n.sub.cladding respectively. The refractive indices then satisfy the inequality: n.sub.rods>n.sub.core>n.sub.cladding and n.sub.buffer. 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.