Evanescent coupling of photodiode with optical waveguide

1. An apparatus comprising:

a semiconductor-based photodiode comprising:

a first region formed in a silicon-on-insulator (SOI) layer and doped with a first conductivity type, wherein a first electrical contact is formed within the first region; and

a second region formed in a block of a semiconductor material other than silicon, wherein the block contacts a top surface of the SOI layer, wherein the second region is doped with a second, different conductivity type, and wherein a second electrical contact is formed within the second region; and

an optical waveguide spaced apart from the SOI layer and evanescently coupled with a depletion region of the photodiode formed at least partly in the block.

2. The apparatus of claim 1 , wherein the depletion region is formed in an intrinsic region of the block.

3. The apparatus of claim 2 ,

wherein the intrinsic region of the block extends along a first dimension, and

wherein at least a portion of the optical waveguide extends parallel to the intrinsic region along the first dimension.

4. The apparatus of claim 3 , wherein the optical waveguide tapers as the optical waveguide extends along the first dimension.

5. The apparatus of claim 3 , wherein the optical waveguide is a first optical waveguide, the apparatus further comprising:

a second optical waveguide evanescently coupled with the first optical waveguide.

6. The apparatus of claim 1 , wherein the optical waveguide is formed of a material other than crystalline silicon.

7. The apparatus of claim 6 , wherein the optical waveguide is formed of one of silicon nitride and silicon oxynitride.

8. The apparatus of claim 1 ,

wherein the semiconductor material comprises one of germanium and indium gallium arsenide.

9. The apparatus of claim 8 , wherein an intrinsic region of the photodiode extends into a recess formed from a surface of the SOI layer.

10. The apparatus of claim 9 , wherein one or both of a p-type region and an n-type region of the photodiode extends into the recess.

11. The apparatus of claim 1 , wherein the optical waveguide defines:

a first side facing the block and extending parallel to the block; and

a second side, opposite the first side, that tapers toward the block in a direction of propagation of an optical signal.

12. The apparatus of claim 1 , wherein the optical waveguide is a curved optical waveguide.

13. The apparatus of claim 12 , wherein the curved optical waveguide comprises:

a curved waveguide section; and

a straight or tapered waveguide section coupled to the curved waveguide section and extending parallel to the block.

14. An apparatus comprising:

a silicon-on-insulator (SOI) layer;

a vertical photodiode formed partly in the SOI layer, wherein a first region having a first electrical contact is formed in the SOI layer and doped with a first conductivity type, wherein a second region having a second electrical contact is formed in a block of a semiconductor material other than silicon, wherein the block contacts a top surface of the SOI layer, and wherein the second region is doped with a second, different conductivity type; and

an optical waveguide spaced apart from the vertical photodiode and side-coupled with a depletion region of the vertical photodiode.

15. The apparatus of claim 14 , wherein the depletion region is formed in an intrinsic region of the block.

16. The apparatus of claim 15 ,

wherein the intrinsic region of the block extends along a first dimension, and

wherein at least a portion of the optical waveguide extends parallel to the intrinsic region along the first dimension.

17. The apparatus of claim 16 , wherein the optical waveguide tapers as the optical waveguide extends along the first dimension.

18. The apparatus of claim 16 , wherein the first dimension is parallel to a surface of the SOI layer.