Electro-optical element

1. An electro-optical element, comprising:

a core layer made of an electro-optical material;

a first clad structure directly on one side of the core layer and configured to form an optical waveguide together with the core layer; and

a second clad structure directly on an opposite side of the core layer and configured to form an optical waveguide together with the core layer;

wherein

(1) the first clad structure comprises a first clad layer and a second clad layer, wherein the first clad layer is directly on the core layer and the second clad layer is directly on the first clad layer, wherein the second clad layer has an dielectric permittivity larger than that of the first clad layer, and wherein the second clad layer has a thickness thicker than that of the first clad layer, and

(2) the second clad structure comprises a first clad layer and a second clad layer, wherein the first clad layer is directly on the core layer and the second clad layer is directly on the first clad layer, wherein the second clad layer has an dielectric permittivity larger than that of the first clad layer, and wherein the second clad layer has a thickness thicker than that of the first clad layer,

a first electrode on the first clad structure, where on the first electrode is on the second clad layer of the first clad structure; and

a second electrode on the second clad structure, where the second electrode is on the second clad layer of the second clad structure.

2. The electro-optical element according to claim 1 , wherein the first clad layers have a thickness smaller than a wavelength of light propagated in the core layer.

3. The electro-optical element according to claim 1 , wherein the second clad layers have a refractive index larger than that of the core layer.

4. The electro-optical element according to claim 3 , wherein the second clad layers have an optical transmittance lower than that of the first clad layer.

5. The electro-optical element according to claim 1 , wherein each of the electrodes comprise at least two kinds of metallic thin films.

6. The electro-optical element according to claim 1 , wherein at least one of the first clad layers and the second clad layers comprises a fine structure.

7. The electro-optical element according to claim 1 , wherein the core layer comprises a polarization-inverted area.

8. The electro-optical element according to claim 1 , wherein the electro-optical material of the core layer comprises one or more of lithium niobate, lithium tantalate, kalium niobate, barium titanate, KTN, STO, BTO, SBN, PLZT, PZT, and DAST.

9. The electro-optical element according to claim 1 , wherein the second clad layers are made of a materials comprising at least one of tantalum oxide, aluminum oxide, hafnium oxide, lithium niobate, lithium tantalate, kalium niobate, barium titanate, KTN, STO, BTO, SBN, PLZT, PZT, and DAST.

10. The electro-optical element according to claim 1 , wherein when an electric field of 10 kV/mm is applied to the core layer, a current density flowing in the core layer is set to be 2 nA/mm 2 or less.

11. The electro-optical element according to claim 1 , wherein the thickness of the first clad layers is less than 20% of the thickness of the core layer.

12. The electro-optical element according to claim 1 , wherein the second clad layers comprise a material having a refractive index larger than the refractive index of the core layer.

13. The electro-optical element according to claim 1 , wherein a ceramic material is attached to the second clad layers.

14. The electro-optical element according to claim 13 , wherein a mixing material in which the ceramic material is dispersed in a resin material is applied to the second clad layer.

15. The electro-optical element according to claim 14 , wherein the ceramic material is deposited on the outer side of the first clad layer.