Optical waveguide device and manufacturing method of optical waveguide device

A manufacturing method of an optical waveguide device that allows light to propagate though a core formed within a cladding formed on a substrate, the core having a higher refractive index than the cladding, the method comprising:

• layering a first cladding-material layer as a lower cladding layer for the cladding and a core-material layer for the core sequentially on the substrate;
• forming the core-material layer into a core having a predetermined waveguide shape, and removing a first part of the core, the first part being positioned at a portion in which a slit is to be formed, to thereby form a gap in the core, wherein L represents a width of the gap in the core;
• layering a second cladding-material layer as an upper cladding layer for the cladding to cover the first cladding-material layer and the core such that the core is buried under the upper cladding layer and the gap having the width L is filled with a material of the upper cladding layer;
• and
• after the gap in the core has been formed, removing, by using dry-etching, a second part of the first and second cladding-material layers, the second part being positioned at the portion in which the slit is to be formed, to thereby form the slit which intersects the gap in the core, wherein:
• W represents a width of the slit in the first and second cladding material layers and the width W of the slit is the same as the width L of the can such that the dry etching forms a slit sidewall having a continuous planar surface that includes the core, the lower cladding laver and the upper cladding layer,
• a depth of the slit is such that the dry etching removes part of substrate,
• the slit is formed by a separate process from the removing a first part of the core to form the gap in the core,
• on a bottom surface of the slit, in a region where the gap is formed by removing the core-material layer, there is no residue of a material of the cladding or the substrate, and
• on the bottom surface of the slit, in a region where the gap is not formed, there exists the residue.