Patent ID: 6975800

Claim:
An optical waveguide having a core material and a cladding material, each of fused silica, wherein the difference between respective linear thermal expansion coefficients of the core material and the cladding material is selected by doping at least one of the core material and the cladding material using at least one foreign substance so that inner mechanical stresses produced in the optical waveguide by manufacturing process are reduced, wherein at least one of the core material and the cladding material is doped using at least one of a first foreign substance and a second foreign substance in such a way that a first ratio of chance in refractive index to change in linear thermal expansion coefficient produced by a doping using the first foreign substance is different from a second ratio of change in refractive index to chance in linear thermal expansion coefficient produced by a doping using the second foreign substance, wherein fluorine and GeO 2 are used as dopants for the cladding material in such concentrations that for a purpose of achieving a difference in the refractive index between the core material and the cladding material of 0.4%, given the same linear thermal expansion coefficients of the core material and the cladding material, the refractive index of the cladding material as compared to pure fused silica is reduced by 0.6% by the fluorine doping alone, and increased by the additional doping with germanium dioxide (GeO b 2 ) by 0.2%, so that the refractive index of the cladding material is less by altogether 0.4% than that of the core material.