Optical waveguide device

1. An optical waveguide device, comprising:

a substrate on which an intermediate layer, a thin-film LN layer of lithium niobate, and a buffer layer are stacked;

an optical waveguide formed in the thin-film LN layer; and

a plurality of electrodes near the optical waveguide,

wherein,

the intermediate layer and the buffer layer contain a same material of a metal element of any one of group 3 to group 18 of a periodic table of elements,

the electrodes are disposed so that respective bottom surfaces thereof are at positions lower than a position of a surface of the buffer layer;

the thin-film LN layer has a plurality of steps provided therein at a predetermined depth from the surface of the buffer layer, and

the electrodes are disposed so that the bottom surfaces thereof are on the steps, respectively.

2. An optical waveguide device, comprising:

a substrate on which an intermediate layer, a thin-film LN layer of lithium niobate, and a buffer layer are stacked;

an optical waveguide formed in the thin-film LN layer; and

a plurality of electrodes near the optical waveguide,

wherein

the intermediate layer and the buffer layer contain a same material of a metal element of any one of group 3 to group 18 of a periodic table of elements,

the electrodes are disposed so that respective bottom surfaces thereof are at positions lower than a position of a surface of the buffer layer;

the intermediate layer has a plurality of steps provided therein at a predetermined depth from the surface of the buffer layer, and

the electrodes are disposed so that the bottom surfaces thereof are on the steps, respectively.

3. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain silicon oxide and an oxide of indium.

4. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain silicon oxide and an oxide of titanium.

5. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain silicon oxide and an oxide of tin.

6. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain silicon oxide and an oxide of germanium.

7. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain silicon oxide and an oxide of zinc.

8. The optical waveguide device according to claim 3 , wherein

the intermediate layer and the buffer layer further contain an oxide of a second metal or a second semiconductor element.

9. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain a mixture or a compound of silicon oxide and an oxide of at least one metal element of group 3 to group 18 of the periodic table of elements.

10. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain a mixture or a compound of silicon oxide and an oxide of at least one semiconductor element excluding silicon.

11. The optical waveguide device according to claim 2 , wherein

the intermediate layer and the buffer layer contain a mixture or a compound of silicon oxide and an oxide containing at least one metal element of any one of group 3 to group 18 of the periodic table of elements and at least one semiconductor element excluding silicon.

12. The optical waveguide device according to claim 2 , wherein

the thin-film LN layer contains an X-cut lithium niobate.

13. The optical waveguide device according to claim 2 , wherein

the buffer layer is stacked on the thin-film LN layer and recesses that occur in the buffer layer corresponding to a shape of the optical waveguide formed in the thin-film LN layer are planarized.