Optical waveguide and method for fabricating the same

An optical waveguide comprising:

• a cladding;
• and
• a core segment buried in said cladding, said core segment serving as a waveguide,
• wherein a glass material constituting said core segment and another glass material constituting said cladding are combined so that an absolute value of difference in coefficient of thermal expansion between said glass materials (α1−α2) is within a range of 0 and 9×10−7/° C., and
• further wherein a yield point of said glass material constituting said core segment is higher than a yield point of said another glass material constituting said cladding by 70° C. or greater,
• where α1 and At1 denote a coefficient of thermal expansion and the yield point of said glass material, and α2 and At2 denote a coefficient of thermal expansion and the yield point of said another glass material.

A method of manufacturing optical waveguide comprising the steps of:

• forming a bonded substrate by pressing and heating a glass plate constituting a lower cladding layer and another glass plate constituting a core layer arranged in a manner that optically polished surfaces thereof abut against each other, to make direct bonding;
• finishing a surface of said core layer of said bonded substrate by one of grinding and polishing, to obtain a thickness appropriate for a core segment;
• forming said core segment defining a waveguide by etching said core layer;
• and
• forming an upper cladding layer by making a film with sputtering over said lower cladding layer, including said core segment, while burying said core segment at the same time into a cladding comprised of said upper cladding layer and said lower cladding layer.

A method of manufacturing optical waveguide comprising the steps of:

• forming a bonded substrate by pressing and heating a glass plate constituting a lower cladding layer and another glass plate constituting a core layer arranged in a manner that optically polished surfaces thereof abut against each other, to make direct bonding;
• finishing a surface of said core layer of said bonded substrate by one of grinding and polishing, to obtain a thickness appropriate for a core segment;
• forming said core segment defining a waveguide by etching said core layer;
• and
• arranging on said core segment an upper cladding layer of glass plate having a yield point lower than a yield point of said core segment, and hot-pressing said upper cladding layer by means of heating and pressing at a temperature at least equal to or higher than the yield point of said upper cladding layer, to bond together said upper cladding layer and said lower cladding layer into an integral body and to bury said core segment at the same time into a cladding while retaining an original shape of said core segment.