High index-contrast fiber waveguides and applications

1. A fiber waveguide having a waveguide axis, comprising:

a first portion extending along the waveguide axis having a refractive index n 1 ; and

a second portion extending along the waveguide axis having a refractive index n 2 ;

wherein |n 1 −n 2 |≧0.3 and the fiber waveguide has an axial optical modulation extending along the waveguide axis.

2. The fiber waveguide of claim 1 , wherein the axial optical modulation has an amplitude of at least 0.1%.

3. The fiber waveguide of claim 2 , wherein the amplitude of the axial optical modulation is at least 5%.

4. The fiber waveguide of claim 1 , wherein the first portion is a core and n 1 >n 2 .

5. The fiber waveguide of claim 1 , wherein the fiber waveguide is a photonic crystal fiber.

6. The fiber waveguide of claim 5 , wherein the photonic crystal fiber has a hollow core.

7. The fiber waveguide of claim 5 , wherein the photonic crystal fiber is a Bragg fiber.

8. The fiber waveguide of claim 1 , wherein the first portion includes chalcogenide glass.

9. The fiber waveguide of claim 8 , wherein structural modulation is a modulation in the fiber waveguide diameter.

10. The fiber waveguide of claim 1 , wherein the axial optical modulation includes a structural modulation.

11. The fiber waveguide of claim 1 , wherein the axial optical modulation is a modulation in the fiber waveguide refractive index.

12. The fiber waveguide of claim 1 , wherein the axial optical modulation forms a Bragg reflector in the fiber waveguide.

13. The fiber waveguide of claim 1 , wherein the axial optical modulation forms an optical cavity in the fiber waveguide.

14. The fiber waveguide of claim 13 , wherein the optical cavity has a resonant wavelength, λ, and a modal volume less than or equal to 500 λ 3 .

15. The fiber waveguide of claim 1 , wherein the axial optical modulation is a periodic axial optical modulation.

16. The fiber waveguide of claim 1 , wherein the axial optical modulation is an aperiodic axial optical modulation.

17. The fiber waveguide of claim 1 , wherein the second portion surrounds the first portion and the first portion includes a nonlinear material.

18. An optical fiber having a waveguide axis, comprising:

a core extending along the waveguide axis having a refractive index, n 1 ; and

a cladding extending along the waveguide axis and surrounding the core, the cladding having a refractive index n 2 <n 1 ; and

an axial optical modulation extending along the waveguide axis forming an optical cavity having a resonant wavelength λ, and a modal volume of less than or equal to 100 λ 3 .

19. The optical fiber of claim 18 , wherein the optical cavity has a modal volume of less than or equal to 10 λ 3 .

20. The optical fiber of claim 18 , wherein the optical cavity has a modal volume of less than or equal to 1 λ 3 .

21. The optical fiber of claim 20 , wherein the axial optical modulation has an amplitude of at least 5%.

22. The optical fiber of claim 18 , wherein the core includes a chalcogenide glass.

23. The optical waveguide of claim 18 , wherein the core includes a nonlinear material.

24. A fiber waveguide device, comprising:

a fiber waveguide having a waveguide axis, wherein the fiber waveguide includes a first portion extending along the waveguide axis having a refractive index n 1 , and a second portion extending along the waveguide axis having a refractive index n 2 , wherein |n 1 −n 2 |≧0.35, an axial optical modulation forming an optical cavity in the fiber waveguide;

wherein during operation an input signal propagating in the fiber waveguide having a power between a first power value, P 1 , and a second power value, P 2 , causes the fiber waveguide to produce an output signal whose output signal power varies nonlinearly with respect to the input signal power.

25. The fiber waveguide device of claim 24 , wherein an input signal power between P 1 and P 2 causes the fiber waveguide to produce an output signal whose output signal power varies discontinuously with respect to the input signal power.

26. The waveguide device of claim 24 , wherein an input signal power below P 1 causes the fiber waveguide to produce an output signal whose output signal power is below an output power value P out,1 , and wherein an input signal power above P 2 causes the fiber waveguide to produce an output signal whose output signal power is above an output power value P out,2 , wherein P out,2 /P out,1 is at least 2.

27. The waveguide device of claim 26 , P out,2 /P out,1 is at least 5.

28. The waveguide device of claim 27 , wherein the ratio P out,2 /P out,1 at least 10.

29. The waveguide device of claim 27 , wherein the ratio P out,2 /P out,1 is at least 100.

30. The fiber waveguide device of claim 24 , wherein the ratio P 1 /P 2 >0.9.

31. The fiber waveguide device of claim 24 , wherein the optical cavity has a quality factor Q and P 1 is less than or equal to 10 8 W/Q 2 .

32. The fiber waveguide device of claim 31 , wherein P 1 is less than or equal to 10 6 W/Q 2 .

33. The fiber waveguide device of claim 32 , wherein P 1 is less than or equal to 10 4 W/Q 2 .

34. The fiber waveguide device of claim 24 , wherein the axial optical modulation forms more than one optical cavity.

35. The fiber waveguide device of claim 24 , wherein the axial optical modulation includes a refractive index modulation.

36. The fiber waveguide device of claim 24 , wherein the axial optical modulation includes a structural modulation.

37. The fiber waveguide device of claim 24 , wherein the fiber waveguide includes a nonlinear material.

38. The fiber waveguide device of claim 37 , wherein the nonlinear material is photorefractive material.

39. The fiber waveguide device of claim 24 , wherein the fiber waveguide is a photonic crystal fiber.

40. The fiber waveguide device of claim 39 , wherein the photonic crystal fiber is a Bragg fiber.

41. The fiber waveguide device of claim 24 , wherein the first portion is a core and n 1 >n 2 .

42. The fiber waveguide device of claim 24 , wherein the fiber waveguide includes a chalcogenide glass.

43. A photonic crystal fiber having a waveguide axis, comprising:

a core region extending along the waveguide axis;

a confinement region extending along the waveguide axis and surrounding the core and comprising a chalcogenide glass; and

an axial optical modulation extending along the waveguide axis forming an optical cavity in the photonic crystal fiber.

44. The photonic crystal fiber of claim 43 , wherein the photonic crystal fiber is a one-dimensionally periodic photonic crystal fiber.

45. The photonic crystal fiber of claim 44 , wherein the photonic crystal fiber is a Bragg fiber.

46. The photonic crystal fiber of claim 43 , wherein the photonic crystal fiber is a two-dimensionally periodic photonic crystal fiber.

47. The photonic crystal fiber of claim 46 , wherein the confinement region is an inhomogeneous region.

48. The photonic crystal fiber of claim 47 , wherein the confinement region includes a holey region having one or more holes extending along the waveguide axis.

49. The photonic crystal fiber of claim 43 , wherein the axial optical modulation has an amplitude of at least 0.01%.