Included are an optical waveguide including a first cladding layer formed on a substrate; a core formed on the first cladding layer; and a second cladding layer formed on the first cladding layer so as to cover the core. At least one of the first cladding layer and the second cladding layer is composed of a cladding material of silicon oxide containing deuterium atoms. The number of hydrogen atoms contained in the cladding material is smaller than the number of the deuterium atoms contained in the cladding material.