Integrated waveguide coupler

1. An integrated waveguide coupler comprising:

a first waveguide comprising a higher refractive index portion that defines a light transmitting direction, a lower refractive index portion being disposed adjacent to the higher refractive index portion in a direction that is transverse to the light transmitting direction;

a second waveguide, comprising a III-V material and disposed near the first waveguide, the first waveguide and the second waveguide facing one another across a gap in the light transmitting direction, such that the first waveguide propagates light in the light transmitting direction, across the gap, toward the second waveguide; and

a connecting waveguide disposed in the gap between the first waveguide and the second waveguide, wherein the connecting waveguide comprises a first material, having a first index of refraction disposed substantially adjacent to the lower refractive index portion, and a second material having a second index of refraction higher than the first index of refraction and disposed substantially between the first waveguide and the second waveguides in the light transmitting direction.

2. The waveguide coupler of claim 1 further comprising a layer of a third material that covers the first waveguide, the second waveguide, and the connecting waveguide, wherein the third material is characterized by a lower index of refraction than effective indices of the higher refractive index portion of the first waveguide, the III-V material, and the second material of the connecting waveguide.

3. The waveguide coupler of claim 2 wherein the third material comprises a passivating oxide.

4. The waveguide coupler of claim 1 wherein an effective index of the higher refractive index portion of the first waveguide is substantially equal to an effective index of the second material of the second waveguide.

5. The waveguide coupler of claim 1 wherein the first waveguide and the second waveguide are coupled along the light transmitting direction and the first waveguide is characterized by a tapered width along the light transmitting direction.

6. A method of fabricating a waveguide coupler, the method comprising:

providing a substrate including a first waveguide and a second waveguide, both waveguides being operable to guide light along a light transmitting direction and spatially separated by a gap in the light transmitting direction, the gap having a bottom surface;

forming a first material in the gap and adjacent to the bottom surface, wherein the first material has a first index; and

forming a second material in the gap, adjacent to the first material and substantially adjacent to the first and second waveguides in the light transmitting direction, wherein the second material has an index higher than the first index.

7. The method of claim 6 wherein the first index is less than an effective index of the first waveguide and the second waveguide.

8. The method of claim 6 wherein the first waveguide comprises silicon material including a ridge guide structure.

9. The method of claim 6 wherein the first material comprises a silicon oxide material.

10. The method of claim 6 wherein the second material comprises an amorphous silicon material.

11. The method of claim 6 wherein forming the first material in the gap comprises a deposition of the first material, a planarization process, and a subsequent etch of the first material.

12. The method of claim 6 wherein forming the second material in the gap comprises a deposition of the second material and a planarization process.

13. The method of claim 6 wherein forming the second material in the gap comprises at least one of only a deposition of the second material or a deposition of the second material and an etch of the second material.

14. The method of claim 6 wherein the first waveguide is tapered in width along the light transmitting direction.

15. An optical device comprising:

a first waveguide region operable to support an optical mode having a peak amplitude and to propagate the optical mode in a light transmitting direction;

a second waveguide region spatially separated from the first waveguide region, in the light transmitting direction, by a separation region;

a multilayer waveguide region disposed in the separation region, wherein the multilayer waveguide region comprises a first material having a first index of refraction positioned below the optical mode and a second material aligned with the peak amplitude and having a second index of refraction higher than the first index of refraction.

16. The optical device of claim 15 further comprising a substrate supporting the first waveguide region, the second waveguide region, and the multilayer waveguide region.

17. The optical device of claim 16 wherein the substrate comprises a silicon substrate.

18. The optical device of claim 15 wherein the first waveguide region comprises a silicon on insulator structure.

19. The optical device of claim 15 wherein the second waveguide region comprises a III-V material structure.

20. The optical device of claim 15 wherein the first material comprises at least one of silicon oxide or silicon nitride and the second material comprises amorphous silicon.