Optical modulator

1. A method of operating an optical modulator,

the optical modulator having:

a rib waveguide which includes a junction which is either a PIN or PN junction, the junction having a breakdown voltage;

the method comprising:

applying a reverse bias to the junction, so as to operate the optical modulator around the breakdown voltage of the junction; and

operating the optical modulator in an avalanche multiplication and/or band-to-band tunnelling mode by increasing the reverse bias past the breakdown voltage,

wherein the breakdown voltage of the junction is less than or equal to 6 V.

2. The method of claim 1 , wherein the breakdown voltage of the junction is between 2 V and 6 V.

3. The method of claim 1 , wherein the rib waveguide includes:

a P+ doped region;

an N+ doped region; and

an intrinsic region, disposed between the P+ doped region and N+ doped region, and

wherein the intrinsic region is between 50 nm and 150 nm thick, such that a PIN junction formed by the P+ doped region, N+ doped region, and the intrinsic region has a breakdown voltage of less than 6 V and is operable in an avalanche multiplication mode.

4. An optical modulator, the optical modulator comprising:

a rib waveguide, the rib waveguide including:

a P+ doped region;

an N+ doped region; and

an intrinsic region, disposed between the P+ doped region and N+ doped region,

wherein the intrinsic region is between 50 nm and 150 nm thick, such that a PIN junction formed by the P+ doped region, N+ doped region, and the intrinsic region has a breakdown voltage of less than 12 V and is operable in an avalanche multiplication mode.

5. The optical modulator of claim 4 , wherein the breakdown voltage is less than or equal to 6 V.

6. The optical modulator of claim 4 wherein the rib waveguide includes an upstanding rib, said upstanding rib having a thickness of between 150 nm and 250 nm.

7. The optical modulator of claim 4 , wherein the rib waveguide includes an upstanding rib, said upstanding rib having a width of between 400 nm and 500 nm.

8. The optical modulator of claim 4 , wherein each of the P+ doped region and the N+ doped region contains dopants with a concentration of between 0.5×10 18 cm −3 and 5×10 18 cm −3 .

9. The optical modulator of claim 4 , wherein the intrinsic region includes dopants with a concentration of between 0.1×10 16 cm −3 and 1×10 16 cm −3 .

10. The optical modulator of claim 4 , further including a P++ doped region adjacent to the P+ doped region and an N++ doped region adjacent to the N+ doped region.

11. The optical modulator of claim 10 , wherein the P++ doped region and N++ doped region include dopants with a concentration of greater than 1×10 19 cm −3 .

12. The optical modulator of claim 11 , wherein the N+ doped region is disposed along an uppermost surface of an upstanding rib of the rib waveguide, and wherein the optical modulator further includes an electrically conductive thin film in contact with the N+ doped region.

13. The optical modulator of claim 12 , wherein the optical modulator further includes a P++ doped region adjacent to the P+ doped region, the P++ doped region including dopants with a concentration of greater than 1×10 19 cm −3 .

14. The optical modulator of claim 12 , wherein the electrically conductive thin film is formed from any one of:

a doped single crystalline Silicon film;

an Indium Tin Oxide (ITO) film; or

a Zinc Oxide (ZnO) film.

15. The optical modulator of claim 4 , wherein the breakdown voltage is between 2 and 6 V.

16. A Mach-Zehnder interferometer based modulator comprising two arms, wherein one arm contains the optical modulator of claim 4 .

17. An optical modulator, the optical modulator comprising:

a rib waveguide, the rib waveguide including:

a P+ doped region; and

an N+ doped region,

wherein the P+ doped region and N+ doped region contain dopants at a concentration of between 1×10 17 and 5×10 18 cm −3 , such that a PN junction formed by the P+ doped region and the N+ doped region has a breakdown voltage of less than 12 V and is operable in a band-to-band tunnelling mode,

wherein the rib waveguide further includes an intrinsic region, disposed between the P+ doped region and N+ doped region, and

wherein the intrinsic region includes dopants with a concentration of between 0.1×10 16 and 1×10 16 cm −3 .

18. The optical modulator of claim 17 , wherein the breakdown voltage is less than or equal to 6 V.

19. The optical modulator of claim 17 , wherein the rib waveguide includes an upstanding rib, said upstanding rib having a thickness of between 150 nm and 250 nm.

20. The optical modulator of claim 17 , wherein the rib waveguide includes an upstanding rib, said upstanding rib having a width of between 400 nm and 500 nm.

21. The optical modulator of claim 17 , wherein each of the P+ doped region and the N+ doped region contains dopants with a concentration of between 0.5×10 18 cm −3 and 5×10 18 cm −3 .

22. The optical modulator of claim 17 , further including a P++ doped region adjacent to the P+ doped region and an N++ doped region adjacent to the N+ doped region.

23. The optical modulator of claim 22 , wherein the P++ doped region and N++ doped region include dopants with a concentration of greater than 1×10 19 cm −3 .

24. The optical modulator of claim 17 , wherein the N+ doped region is disposed along an uppermost surface of an upstanding rib of the rib waveguide, and wherein the optical modulator further includes an electrically conductive thin film in contact with the N+ doped region.

25. The optical modulator of claim 24 , wherein the optical modulator further includes a P++ doped region adjacent to the P+ doped region, the P++ doped region including dopants with a concentration of greater than 1×10 19 cm −3 .

26. The optical modulator of claim 17 , wherein the breakdown voltage is between 2 and 6 V.

27. A Mach-Zehnder interferometer based modulator comprising two arms, wherein one arm contains the optical modulator of claim 17 .