Electro-optic waveguide device and optical module

1. An electro-optic waveguide device comprising:

a slot waveguide including a lower high-refractive-index layer with a first refractive index and an upper high-refractive-index layer with a second refractive index,

wherein the lower high-refractive-index layer and the upper high-refractive-index layer have conductivity and are disposed to face each other with a gap; and

a slot part formed as a low-refractive-index layer,

wherein the low-refractive-index layer is formed of a material producing an electro-optic effect and has a third refractive index lower than the first refractive index and the second refractive index,

wherein the low-refractive-index layer is formed in the gap to come into contact with the lower high-refractive-index layer and the upper high-refractive-index layer,

wherein one of the lower high-refractive-index layer or the upper high-refractive-index layer includes a stretch stretching beyond both sides of a contact portion with the slot part in a width direction intersecting a transmission direction of the slot waveguide,

at least a portion of the stretch remaining planar with the contact portion, and

the contact portion spanning, in the width direction, for an entire width of the slot part where the slot part makes contact with the one of the lower high-refractive-index layer or the upper high-refractive-index layer, and

wherein another one of the lower high-refractive-index layer or the upper high-refractive-index layer includes portions facing the stretch in a cross-sectional shape in the width direction.

2. The electro-optic waveguide device of claim 1 , wherein

the other one of the lower high-refractive-index layer or the upper high-refractive-index layer includes another stretch, and

the stretch and the other stretch include portions facing each other.

3. The electro-optic waveguide device of claim 2 , wherein

the slot part has a strip shape extending in the transmission direction, and

the gap is located at the contact portion, and

the stretch and the other stretch layer are equal to each another.

4. The electro-optic waveguide device of claim 3 , further comprising:

a clad layer that contacts side surfaces of the low-refractive-index layer, has a refractive index lower than the low-refractive-index layer, and is disposed in the gap.

5. The electro-optic waveguide device of claim 2 , wherein the contact portion is formed in a rib shape and extends in the transmission direction.

6. The electro-optic waveguide device of claim 5 , wherein

the low-refractive-index layer has a width larger than the slot part, and

clad layers with a refractive index lower than the low-refractive-index layer are disposed in the gap.

7. The electro-optic waveguide device of claim 1 , further comprising:

a lower contact region configured to have an electric resistance lower than the lower high-refractive-index layer and to electrically connect the lower high-refractive-index layer to an electrode; and

an upper contact region configured to have an electric resistance lower than the upper high-refractive-index layer and to electrically connect the upper high-refractive-index layer to an electrode.

8. The electro-optic waveguide device of claim 7 , wherein the lower contact region and the upper contact region are disposed to come into contact with the lower high-refractive-index layer or the upper high-refractive-index layer at positions spaced with the slot part in the width direction.

9. The electro-optic waveguide device of claim 1 , wherein a contact portion of the lower high-refractive-index layer and a contact portion of the upper high-refractive-index layer with the slot part face each other in parallel.

10. The electro-optic waveguide device of claim 1 , wherein

in regard to an electric field generated between the lower high-refractive-index layer and the upper high-refractive-index layer when a voltage is applied, dimensions of the stretch, in a horizontal direction, are determined so that a reducing rate of an electric field intensity at end portions compared to a middle portion of the slot part in the width direction is set to a predetermined value.

11. An optical module comprising:

electro-optic waveguide device comprising:

a slot waveguide including a lower high-refractive-index layer with a first refractive index and an upper high-refractive-index layer with a second refractive index,

wherein the lower high-refractive-index layer and the upper high-refractive-index layer have conductivity and are disposed to face each other with a gap; and

a slot part formed as a low-refractive-index layer,

wherein the low-refractive-index layer is formed of a material producing an electro-optic effect and has a third refractive index lower than the first refractive index and the second refractive index,

wherein the low-refractive-index layer is formed in the gap to come into contact with the lower high-refractive-index layer and the upper high-refractive-index layer,

wherein one of the lower high-refractive-index layer or the upper high-refractive-index layer includes a stretch stretching beyond both sides of a contact portion with the slot part in a width direction intersecting a transmission direction of the slot waveguide,

at least a portion of the stretch remaining planar with the contact portion, and

the contact portion spanning, in the width direction, for an entire width of the slot part where the slot part makes contact with the one of the lower high-refractive-index layer or the upper high-refractive-index layer, and

wherein another one of the lower high-refractive-index layer or the upper high-refractive-index layer includes portions facing the stretch in a cross-sectional shape in the width direction;

a light source optically connected to the electro-optic waveguide device; and

a medium for transmitting light passing through the electro-optic waveguide device.

12. The optical module of claim 11 , wherein

the other one of the lower high-refractive-index layer and the upper high-refractive-index layer includes another stretch, and

the stretch and the other stretch include portions facing each other.

13. The optical module of claim 12 , wherein

the slot part has a strip shape extending in the transmission direction, and

the gap is located at the contact portion, and

the stretch and the other stretch are equal to each another.

14. The optical module of claim 13 , further comprising:

a clad layer that contacts side surfaces of the low-refractive-index layer, has a refractive index lower than the low-refractive-index layer, and is disposed in the gap.

15. The optical module of claim 12 , wherein the contact portion is formed in a rib shape and extends in the transmission direction.

16. The optical module of claim 15 , wherein

the low-refractive-index layer has a width larger than the slot part, and

clad layers with a refractive index lower than the low-refractive-index layer are disposed in the gap.

17. The optical module of claim 11 , further comprising:

a lower contact region configured to have an electric resistance lower than the lower high-refractive-index layer and to electrically connect the lower high-refractive-index layer to an electrode; and

an upper contact region configured to have an electric resistance lower than the upper high-refractive-index layer and to electrically connect the upper high-refractive-index layer to an electrode.

18. The optical module of claim 17 , wherein the lower contact region and the upper contact region are disposed to come into contact with the lower high-refractive-index layer or the upper high-refractive-index layer at positions spaced with the slot part in the width direction.

19. The optical module of claim 11 , wherein a contact portion of the lower high-refractive-index layer and a contact portion of the upper high-refractive-index layer with the slot part face each other in parallel.

20. The optical module of claim 11 , wherein

in regard to an electric field generated between the lower high-refractive-index layer and the upper high-refractive-index layer when a voltage is applied, dimensions of the stretch, in a horizontal direction, are determined so that a reducing rate of an electric field intensity at end portions compared to a middle portion of the slot part in the width direction is set to a predetermined value.