Optical waveguide devices

1. An optical waveguide device comprising;

a thin layer consisting of an optical material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate, wherein said optical material is optionally doped with a metal element or a rare earth element; and

a ridge portion loaded directly on said thin layer, said ridge portion comprising tantalum pentoxide and having a trapezoidal shape viewed in a cross section perpendicular to a direction of propagation of a light,

wherein said ridge portion directly contacts said optical material; and

wherein said light is confined to and propagates in said thin layer under said ridge portion.

2. The device of claim 1 , wherein said ridge portion comprises an inclined face having a rising angle of 45° or larger and 80° or smaller viewed in said cross section perpendicular to said direction of propagation of light.

3. The device of claim 1 , further comprising a supporting body provided on a first side of said thin layer, said first side being opposite to a second side of said thin layer on which said ridge portion is loaded.

4. The device of claim 1 , wherein said thin layer is exposed to both sides of said ridge portion viewed in said cross section perpendicular to said direction of propagation of light.

5. The device of claim 1 , further comprising covering layers on both sides of said ridge portion viewed in said cross section perpendicular to said direction of propagation of light.

6. The device of claim 1 , further comprising a periodic domain inversion structure formed in said thin layer.

7. The device of claim 1 , further comprising a silicon dioxide film at least on said ridge portion.

8. The device of claim 1 , wherein said ridge portion is formed by wet etching.

9. A method of producing an optical waveguide, comprising the steps of:

providing a thin layer consisting of an optical material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate, said optical material optionally doped with a metal element or a rare earth element; and

providing a ridge portion on said thin layer by wet etching, said ridge portion comprising tantalum pentoxide and having a trapezoidal shape viewed in a cross section perpendicular to a direction of propagation of light, wherein said ridge portion directly contacts said optical material; and

wherein said light is confined to and propagates in said thin layer under said ridge portion.

10. The method of claim 9 , wherein said ridge portion comprises an inclined face having a rising angle of 45° or larger and 80° or smaller viewed in said cross section perpendicular to said direction of propagation of light.

11. The method of claim 9 , further comprising the step of providing said thin layer on a supporting body before providing said ridge portion on said thin layer.

12. The method of claim 9 , further comprising the step of providing covering layers on both sides of said ridge portion viewed in said cross section perpendicular to said direction of propagation of light.

13. The method of claim 9 , further comprising the step of providing a periodic domain inversion structure in said thin layer.

14. The method of claim 9 , further comprising the step of providing a silicon dioxide film on said ridge portion.

15. The device of claim 1 , wherein said optical material is doped with said metal element or said rare earth element.

16. The device of claim 1 , wherein said optical material is selected from the group consisting of lithium niobate and lithium tantalate.

17. The method of claim 9 , wherein said optical material is selected from the group consisting of lithium niobate and lithium tantalate.