An optical waveguide includes a first cladding, a second cladding, and a core. The core is embedded in the first cladding so as to be exposed on one principal surface of the first cladding that is opposed to the second cladding. The first cladding and the second cladding are arranged so as to sandwich the core. The core is a product formed by a reaction in which a polymeric material that includes branched polysilane and polysiloxane is subjected to at least one process selected from heating and ultraviolet irradiation. The refractive index of the core is higher than the refractive indices of the first cladding and the second cladding.

An optical waveguide device is provided with a core formed on a substrate and a clad layer. A low-temperature film-forming method, such as the CVD or PVD method, is used in a core forming process for forming the core and a clad forming process for forming the clad layer. The surface of the clad layer is coated with a protective film of chrome or the like in a protective film forming process that is carried out after the clad forming process. In a heating/pressurizing process that is carried out after the protective film forming process, the clad layer is heated and pressurized from its outside by the HIP (hot isostatic pressing) method. This heating/pressurizing process substantially eliminates voids in the clad layer and the like, and enhances or improves the density of a buffer layer, core, and upper clad layer and the transparency of the core layer. The protective film is removed by etching or the like in a removing process.

Proposed is a method for fabricating a planar optical waveguide device having a plurality of core segments formed between a lower clad layer and an upper clad layer, in which a hot isostatic pressing process (HIP) is carried out during the fabrication process. The lower clad layer may consist of a substrate or a buffer layer formed on a substrate. Each layer may be formed either by a low-temperature film-forming process such as CVD or by the flame hydrolysis pressing process. The HIP process is also effective in eliminating voids when the core is formed in a recess of the lower clad layer. According to the tests conducted by the inventors, it was found that the HIP process can be conducted without requiring any protective layer or a gas barrier through proper selection of the condition for the HIP process, as opposed to the common belief that a protective layer or a gas barrier is essential for the HIP process.

An optical waveguide component has a first optical member in which a predetermined first core pattern groove is formed and a second optical member in which a predetermined second core pattern groove is formed, the first and second optical members being combined together so that said first and second core pattern grooves are opposingly overlapped with each other, and the first and second core pattern grooves being filled with a core material.

An optical waveguide component has a first optical member in which a predetermined first core pattern groove is formed and a second optical member in which a predetermined second core pattern groove is formed, the first and second optical members being combined together so that said first and second core pattern grooves are opposingly overlapped with each other, and the first and second core pattern grooves being filled with a core material.