Thermally diffused multi-core waveguide

A thermally diffused dual-core (TDDC) waveguide is provided that has a pair of spaced cores 12,14 disposed within a cladding 16. The waveguide 10 is formed of a glass material having the appropriate dopants to allow light 15 to propagate in either direction along the cores 12,14. The TDDC waveguide is formed by heating a portion 22 of the dual-core waveguide 10 to symmetrically diffuse the dopants of the cores 12,14 into the cladding 16. Consequently, the optical mode fields of the cores spread beyond the optical mode field of each original core such that the optical field in one core 12 excites the optical field in the adjacent core 14 to optically couple the two cores 12,14. The amount of diffusion of the core into the cladding is dependent on the temperature of the heat and the time the heat is applied to the dual-core waveguide. The cores may be diffused so that the cores overlap to thereby create a unitary core. The TDDC waveguide may be used to provide a coupler or wavelocker device.