METHOD FOR MAPPING OF DISPERSION AND OTHER OPTICAL PROPERTIES OF OPTICAL WAVEGUIDES

• US 20090079967A1
• Filed: 09/18/2008
• Published: 03/26/2009
• Est. Priority Date: 09/20/2007
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Radic, Stojan
• Granted Patent: US 7,796,244 B2
• Time in Patent Office: Days
• US Class Current: 356/73.100
• CPC Class Codes: G01M 11/319 Reflectometers using stimulated back-scatter, e.g. Raman or fibre amplifiers
• CPC Class Codes: G01M 11/338 by measuring dispersion other than PMD, e.g. chromatic dispersion
• CPC Class Codes: G01M 11/39 in which light is projected from both sides of the fiber or waveguide end-face

Abstract

A method is provided for measurement of dispersion or other optical and mechanical properties within a waveguide by inducing four-photon mixing at different locations within the waveguide by timing a pump signal to counter-collide with and abruptly amplify or attenuate one or both of a probe pulse and a signal pulse at each location. The measurement of the components of the resulting mixing signal created by each collision is used to calculate dispersion defined by the location at which the collision occurred. By combining the measurements from all of the locations, a spatial map of dispersion or other optical or mechanical properties within the waveguide can be generated.

Claims

1. A method for measurement of dispersion or other optical, mechanical or material properties of a waveguide, comprising:

localizing four-photon mixing at a plurality of different locations within the waveguide by timing a pump pulse to counter-collide with and abruptly modify the amplitude of one or both of a probe pulse and a signal pulse at each location;

measuring the power of each of four waves comprising a mixed signal at an output of the waveguide for each of the different locations; and

combining the measurements to generate a spatial map of dispersion or other properties within the waveguide.

2. The method of claim 1, wherein the modification comprises amplification of one or both of the probe pulse and signal pulse.

3. The method of claim 2, wherein an amplitude of the pump pulse is greater than an amplitude of the probe pulse and the signal pulse.

4. The method of claim 2, wherein an amplitude of the probe pulse and an amplitude of the signal pulse are sufficiently low so that mixing terms with adequate powers are not generated without the pump pulse.

5. The method of claim 1, wherein the modification comprises attenuation of one or both of the probe pulse and signal pulse.

6. The method of claim 5, wherein the pump pulse has an amplitude which is lower than the amplitude of the probe pulse and signal pulse.

7. The method of claim 6, wherein the amplitude of the probe pulse and the signal pulse after attenuation are sufficiently low so that mixing terms with adequate powers are not generated after the counter-colliding attenuation.

8. The method of claim 1, wherein the waveguide has a length on the order of kilometers and the modification of the amplitude of one of the signal pulse and the probe pulse is produced by stimulated Brillouin scattering.

9. The method of claim 1, wherein the waveguide has a length on the order of meters and the modification of the amplitude of one of the signal pulse and the probe pulse is produced by stimulated Raman scattering.

10. The method of claim 1, wherein the waveguide is a highly nonlinear fiber.

11. The method of claim 1, wherein the waveguide is a general, solid core optical fiber facilitating a four-photon mixing process.

12. The method claim 2, wherein polarizations of each of the probe pulse, signal pulse and the pump pulse are aligned in order to produce a deterministic four-photon mixing term.

13. The method of claim 12, wherein the polarizations are aligned to maximize a gain produced by the countercolliding amplification.

14. The method of claim 5, wherein polarizations of each of the probe pulse, signal pulse and the pump pulse are aligned in order to produce deterministic four-photon mixing term.

15. The method of claim 14, wherein the polarizations are aligned to maximize a loss produced by the countercolliding attenuation.

16. The method of claim 1, wherein the pump pulse and the probe pulse are launched at orthogonal states and either the pump pulse or the probe pulse is reflected from a Faraday mirror, whereby active polarization tracking for each pump-probe or pump-signal collision instance is avoided or minimized.

17. The method of claim 1, wherein the pump pulse has a predetermined polarization state for facilitating optical power transfer from the pump pulse to one or both of the probe pulse and signal pulse.

18. The method of claim 1, further comprising actively controlling the polarization state at the collision of one or both of the probe pulse and signal pulse with the counterpropagating pump pulse.

19. The method of claim 1, further comprising passively controlling the polarization state at the collision of one or both of the probe pulse and signal pulse with the counterpropagating pump pulse.

20. The method of claim 19, further comprising controlling the polarization states between the pump pulse and signal pulse to be orthogonal polarization states while controlling the polarization state between the signal pulse and probe pulse to be copolarized polarization states.

21. The method of claim 20, further comprising launching the pump pulse and probe pulse into the waveguide using a polarization beam combiner to control the polarization states to be orthogonal.

22. The method of claim 21, further comprising altering the probe and the signal pulse polarization state by reflection from the Faraday mirror to facilitate collision with the pump pulse.

23. The method of claim 1, further comprising controlling the bias of a modulator used to launch frequency locked pump and signal pulses into the waveguide prior to four-photon mixing, whereby pump-signal power transfer outside a defined collision window is minimized.

24. A method for measurement of dispersion or other optical properties in an optical waveguide, comprising:

inserting a probe pulse with a measured amplitude into the waveguide in a first direction traveling from a first end toward a second end of the waveguide;

inserting a signal pulse with a measured amplitude into the waveguide in the first direction, wherein the probe amplitude and the signal amplitude are sufficiently low that probe and signal mixing results in negligible optical power;

inserting a counter-propagating signal having a second amplitude larger than at least one of the probe amplitude and the signal amplitude into the second end of the waveguide, wherein the counter-propagating signal is timed to collide with and abruptly amplify one or both of the probe and the signal at a first collision coordinate within the waveguide so that a mixed signal is produced;

measuring the power of the mixed signal at the second end;

repeating the steps of inserting a probe, inserting a signal, inserting a counter-propagating signal and measuring at a plurality of different collision coordinates along the waveguide until a desired length of the waveguide has been tested; and

combining the measured powers for all collision coordinates to generate a spatial map of the optical properties of the waveguide.

25. The method of claim 24, wherein the waveguide has a length on the order of kilometers and the amplification of one of the signal pulse and the probe pulse is produced by stimulated Brillouin scattering.

26. The method of claim 24, wherein the waveguide has a length on the order of meters and the amplification of one of the signal pulse and the probe pulse is produced by stimulated Raman scattering.

27. The method of claim 24, wherein the waveguide is a highly nonlinear fiber.

28. The method claim 24, wherein polarizations of each of the probe pulse, the signal pulse and the pump signal are aligned.

29. The method of claim 28, wherein the polarizations are aligned to maximize a gain produced by the amplification.

30. The method of claim 24, wherein the pump signal and the probe pulse are launched at orthogonal states for polarization insensitivity.

31. A method for localization of four-photon mixing within an optical waveguide, comprising:

launching a probe pulse and a signal pulse into an input end of an optical waveguide, the probe pulse and signal pulse comprising weak pulses having amplitudes insufficient to produce significant four-photon mixing;

abruptly amplifying at least one of the probe pulse and signal pulse by a first counterpropagating pump pulse at a selected waveguide target window in the waveguide, the amplification being sufficient for significant four-photon generation by signal-probe pulse mixing;

measuring a power and phase of the mixed signal generated by the pulse mixing;

storing the measured power and phase of the mixed signal on a storage medium; and

computing a property of the waveguide using the stored data.

32. The method of claim 31, further comprising attenuating the or each amplified pulse outside the target window by a second counterpropagating pump pulse to a level sufficient to prevent significant four-photon generation by signal-probe pulse mixing outside the target window, whereby the computed waveguide property is localized at the target window.

33. The method of claim 31, further comprising launching the first counterpropagating pump pulse at a predetermined time interval after launching of said at least one of the probe pulse and signal pulse, whereby the pulse amplification is spatially defined.

34. The method of claim 32, further comprising launching the second counterpropagating pump pulse at a predetermined time interval from the amplification, whereby the pulse attenuation is spatially defined.

35. The method of claim 31, wherein said signal pulse is amplified by the first counterpropagating pump pulse.

36. The method of claim 31, wherein said probe pulse is amplified by the first counterpropagating pump pulse.

37. The method of claim 31, wherein both said signal pulse and said probe pulse are amplified by the first counterpropagating pump pulse.

38. The method of claim 32, wherein said signal pulse is attenuated by the second counterpropagating pump pulse.

39. The method of claim 32, wherein said probe pulse is attenuated by the second counterpropagating pump pulse.

40. The method of claim 32, wherein both said signal pulse and said probe pulse are attenuated by the second counterpropagating pump pulse.

41. The method of claim 31, wherein the amplification step comprises spatially localized amplification of said at least one pulse by collision with the first counterpropagating pump pulse positioned at the Brillouin frequency required to facilitate optical power transfer from the counterpropagating pump pulse to said at least one pulse.

42. The method of claim 32, wherein the attenuation step comprises spatially localized attenuation of said at least one pulse by collision with the second counterpropagating pump pulse positioned at the Brillouin frequency required to facilitate optical power transfer from said at least one pulse to the second counterpropagating pump pulse.

43. The method of claim 42, wherein the optical power of the counterpropagating pump pulse is lower than that of said at least one pulse prior to the collision instance.

44. The method of claim 31, wherein the first counterpropagating pump pulse has a predetermined polarization state for facilitating optical power transfer from the first counterpropagating pump pulse to said at least one pulse during amplification.

45. The method of claim 32, wherein the second counterpropagating pump pulse has a predetermined polarization state for facilitating optical power transfer from the second counterpropagating pump pulse to said at least one pulse during attenuation.

46. A method of abrupt power adjustment in an optical waveguide, comprising:

launching a probe pulse and a signal pulse into a first end of an optical waveguide;

inserting a counterpropagating pump pulse into a second end of the waveguide, the counterpropagating pump pulse having a different amplitude from the probe pulse and signal pulse, wherein the counterpropagating pump pulse is timed to collide with and abruptly modify the amplitude of one or both of the signal and probe pulses by power transfer at selected location in the waveguide; and

obtaining information from the modified signal output at the second end of the optical waveguide.

47. The method of claim 46, wherein the modification comprises amplification of at least one of the probe pulse and signal pulse, the amplification being sufficient for significant four-photon generation by signal-probe pulse mixing.

48. The method of claim 46, wherein the modification comprises attenuation of at least one of the probe pulse and signal pulse.

49. The method of claim 46, wherein the modification comprises amplification of both the probe pulse and the signal pulse.

50. The method of claim 46, wherein the amplitude modification of the at least one pulse is spatially defined by timing between the forward propagating signal or probe pulse and the counterpropagating pump pulse.

51. The method of claim 46, wherein the amplitude modification is spatially defined by positioning the counterpropagating pump pulse for collision with the probe or signal pulse at the Brillouin frequency required to facilitate optical power transfer between the colliding pulses.

52. The method of claim 46, wherein the polarization states of the probe or signal pulse and the counterpropagating pump pulse are actively controlled.

53. The method of claim 46, wherein the polarization states of the probe or signal pulse and the counterpropagating pump pulse are passively controlled.

54. The method of claim 53, wherein the polarization states are controlled to be orthogonal polarization states by a polarization beam combiner.

55. The method of claim 53, wherein the probe pulse and signal pulse polarization states are controlled by reflection from a Faraday mirror.

56. The method of claim 47, further comprising measuring the power and phase of the mixed signal generated by the pulse mixing, using the measured power and phase to compute an output which corresponds to a property of the waveguide, and providing the output on a medium accessible by a user.

57. The method of claim 46, further comprising controlling the power transfer to alter the pulse waveform of at least one of the signal and probe pulses in a predetermined manner, whereby information content carried by the at least one pulse is modified.