Enhancing the performance of light sensors that receive light signals from an integrated waveguide

1. An optical device, comprising:

a light sensor on a base; and

a waveguide on the base such that a light signal guided by the waveguide is received at the light sensor, the waveguide including a taper configured such that a ratio of a width of the waveguide at a first location in the taper:the width of the waveguide at a second location in the taper is greater than 1.2:1 where a length of the taper between the first location and the second location is less than 20 μm.

2. The device of claim 1 , wherein the first location is at the wide end of the taper and the second location is at the narrow end of the taper.

3. The device of claim 1 , wherein the waveguide is partially defined by a ridge extending from slab regions, the slab regions being on opposing sides of the ridge, and the width of the waveguide is equal to the width of the ridge.

4. The device of claim 3 , wherein a ratio of a thickness of a slab region:a thickness of the ridge is less than 1:5.

5. The device of claim 3 , wherein a wide end of the taper has a ratio of a thickness of a slab region:a width of the ridge less than 1:1.

6. The device of claim 1 , wherein

the light sensor includes a light-absorbing medium positioned to receive at least a portion of the light signal from the waveguide,

the light sensor includes a ridge extending upwards from slab regions and the light-absorbing medium is included in the ridge and also in the slab regions,

the light-absorbing medium includes doped regions positioned such that an application of a reverse bias between the doped regions forms an electrical field in the light-absorbing medium included in the ridge.

7. The device of claim 6 , wherein the doped regions are positioned on opposing sides of the ridge.

8. The device of claim 6 , wherein the light-absorbing medium included in each slab region is continuous with the light-absorbing medium included in the ridge.

9. The device of claim 1 , wherein the first location is at a wide end of the taper and the second location is at a narrow end of the taper and the length of the taper between the first location and the second location is less than 10 μm.

10. The device of claim 9 , wherein the length of the taper between the first location and the second location is less than 5 μm.

11. The device of claim 1 , wherein the width of the waveguide at the first location is greater than 2 μm.

12. The device of claim 11 , wherein the width of the waveguide at the first location is greater than 3 μm.

13. The device of claim 1 , wherein a height of the waveguide is greater than 2 μm.

14. The device of claim 13 , wherein the height of the waveguide is greater than 3 μm.

15. The device of claim 13 , wherein the device is built on a silicon-on-insulator wafer and the waveguide is a ridge waveguide, and the height of the waveguide is a distance between a top of the ridge and an optical insulator of the silicon-on-insulator wafer.

16. The device of claim 1 , wherein the device excludes an output waveguide that carries the light signal away from the light sensor.

17. The device of claim 1 , wherein the light signal travels on an optical path through the waveguide, the optical path of the light signal having a constant thickness from a location before the taper and through the taper.

18. The device of claim 1 , wherein the light signal travels on an optical path through the waveguide, the optical path does not expand vertically as the light signal enters the taper from a location before the taper.

19. The device of claim 1 , wherein the second location is between the light sensor and the first location.

20. The device of claim 19 , wherein the first location is at a wide end of the taper and the second location is at a narrow end of the taper, the length of the taper between the first location and the second location is less than 10 μm, and the ratio is greater than 2.5.