Integrated waveguide coupler

1. An integrated waveguide coupler comprising:

a first waveguide, the first waveguide comprising:

a higher refractive index portion; and

a lower refractive index portion, adjacent to the higher refractive index portion of the first waveguide;

a second waveguide, the second waveguide comprising:

a higher refractive index portion; and

a lower refractive index portion, adjacent to the higher refractive index portion of the second waveguide;

a third waveguide between the first waveguide and the second waveguide;

a first region between the first waveguide and the third waveguide, wherein:

the first region separates the first waveguide from the third waveguide;

the first region comprises a first material having a first index of refraction;

the first region comprises a second material having a second index of refraction;

the second index of refraction is higher than the first index of refraction;

the second material is different from material of the higher refractive index portion of the first waveguide; and

the second material is different from material of the third waveguide; and

a second region between the second waveguide and the third waveguide, wherein:

the second region separates the second waveguide from the third waveguide;

the second region comprises a third material having a third index of refraction;

the second region comprises a fourth material having a fourth index of refraction;

the fourth index of refraction is higher than the third index of refraction;

the fourth material is different from material of the higher refractive index portion of the second waveguide; and

the fourth material is different from material of the third waveguide.

2. The integrated waveguide coupler of claim 1 , wherein:

the first material is a silicon oxide; and

the third material is a silicon oxide.

3. The integrated waveguide coupler of claim 1 , wherein:

the second material is amorphous silicon; and

the fourth material is amorphous silicon.

4. The integrated waveguide coupler of claim 3 , wherein:

the first waveguide is a first silicon-on-insulator waveguide;

the second waveguide is a second silicon-on-insulator waveguide; and

the third waveguide comprises III-V material.

5. The integrated waveguide coupler of claim 1 , wherein the third waveguide comprises a gain medium for a laser.

6. The integrated waveguide coupler of claim 1 , wherein:

the first waveguide is tapered along a light-transmitting direction of the first waveguide; and

the third waveguide is tapered along a light-transmitting direction of the third waveguide.

7. The integrated waveguide coupler of claim 1 , wherein the first waveguide comprises a ridge structure.

8. A method of fabricating an integrated waveguide coupler, the method comprising:

forming a first material in a first gap, wherein:

the first gap is between a first waveguide and a second waveguide; and

the first material has a first index of refraction;

forming a second material in the first gap, wherein:

the second material is formed in the first gap after forming the first material in the first gap;

the second material has a second index of refraction; and

the second index of refraction is greater than the first index of refraction;

forming a third material in a second gap, wherein the second gap is between the second waveguide and a third waveguide;

forming a fourth material in the second gap, wherein the fourth material is formed in the second gap after forming the third material in the second gap.

9. The method of fabricating an integrated waveguide coupler as recited in claim 8 , the method further comprising applying a fifth material that covers the first waveguide, the third waveguide, the second material formed in the first gap, and the fourth material formed in the second gap.

10. The method of fabricating an integrated waveguide coupler as recited in claim 8 , the method further comprising:

etching the first material formed in the first gap before forming the second material in the first gap; and

etching the third material formed in the second gap before forming the fourth material in the second gap.

11. The method of fabricating an integrated waveguide coupler as recited in claim 10 , the method further comprising a planarization process of the first material before etching the first material.

12. The method of fabricating an integrated waveguide coupler as recited in claim 8 , wherein:

the third material is the same as the first material; and

the fourth material is the same as the second material.

13. The method of fabricating an integrated waveguide coupler as recited in claim 8 , wherein:

the second material is amorphous silicon; and

the fourth material is amorphous silicon.

14. The method of fabricating an integrated waveguide coupler as recited in claim 8 , wherein the third waveguide comprises a gain medium for a laser.

15. An optical device, the optical device comprising:

a first waveguide region configured to support an optical mode;

a second waveguide region configured to support the optical mode;

a third waveguide region, wherein:

the third waveguide region is separated from the first waveguide region by a first separation region; and

the third waveguide region is separated from the second waveguide region by a second separation region;

a first multilayer waveguide region is disposed in the first separation region, the first multilayer waveguide region comprising:

a first material having a first index of refraction; and

a second material having a second index of refraction, wherein the second index of refraction is greater than the first index of refraction; and

a second multilayer waveguide region disposed in the second separation region, the second multilayer waveguide region comprising:

a third material having a third index of refraction; and

a fourth material having a fourth index of refraction.

16. The optical device as recited in claim 15 , wherein:

the first material is the same as the third material; and

the fourth material is the same as the second material.

17. The optical device as recited in claim 15 , wherein:

the first material is a silicon oxide; and

the second material is amorphous silicon.

18. The optical device as recited in claim 15 , wherein the third waveguide region comprises a gain medium for a laser.

19. The optical device as recited in claim 18 , wherein the first waveguide region and the second waveguide region are silicon-on-insulator waveguides.

20. The optical device as recited in claim 15 , wherein:

the first waveguide region comprises a first ridge structure; and

the second waveguide region comprises a second ridge structure.