Optical device having a stepwise or tapered light input/output part and manufacturing method therefor
An optical device includes an optical waveguide provided on a principal surface of a substrate. The optical waveguide includes a core and a cladding provided around the core. The cladding is configured by a substance having a refractive index smaller than 71.4% of the refractive index of the core. The core has constituent atoms substantially forming a diamond lattice structure. The optical waveguide has a light input/output part through which a light beam is input and/or output. The light input/output part decreases stepwise in thickness towards an output end while tapering down in its width. The core is provided in the light input/output part to have a (111) plane or an equivalent plane to the (111) plane exposed on a face of a riser of the stepwise thickness of the light input/output part.
1. An optical device comprising an optical waveguide provided on a principal surface of a substrate, said optical waveguide comprising:
a core formed by patterning a single-crystalline film which has constituent atoms substantially forming a diamond lattice structure and has a surface being neither a (111) plane nor an equivalent plane to the (111) plane;
a first cladding formed by covering the core with a substance having a refractive index smaller than 71.4% of the refractive index of the core; and
a light input/output part through which a light beam is input or output,
the light input/output part having two or more planes selected from a (111) plane and an equivalent plane to the (111) plane, which expose as etch-stop planes when a precursor tapered in width toward an end portion of the light input/output part is wet etched using an alkaline solution, and the core having two planes substantially non-parallel to each other among the (111) plane and the equivalent plane.
2. The optical device according to claim 1 , wherein the connective part has a plurality of sub-connective parts arrayed in series in a direction of light propagation,
each of the sub-connective parts having a sub-connective plane as a slope, and a sub-plane connected to the sub-connective plane and having a same plane orientation as a top face of the core,
the sub-connective planes having the same plane orientation for all of the plurality of sub-connective parts, and being configured to shrink stepwise in area in the direction of light propagation.
3. The optical device according to claim 1 , wherein the light input/output part has an end portion truncated substantially perpendicularly to a direction of light propagation, ensuring a size of cross section capable of allowing both of TE wave and TM wave to propagate therethrough.
4. The optical device according to claim 1 , wherein the light input/output part has provided therearound with a second cladding having a refractive index substantially larger than that of the first cladding and substantially smaller than that of the core,
the first cladding extending around the second cladding.
5. The optical device according to claim 1 , wherein the precursor before wet-etching has a uniform thickness.