Method and apparatus for measuring waveform of optical signal

• US 6,456,380 B1
• Filed: 05/15/2000
• Issued: 09/24/2002
• Est. Priority Date: 05/19/1999
• Status: Expired due to Fees

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Naganuma, Kazunori
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US09/570,889
• Time in Patent Office: 862 Days
• Field of Search: 356/450, 356/451, 356/484, 356/491
• US Class Current: 356/450
• CPC Class Codes: G01J 11/00 Measuring the characteristics of individual optical pulses or of optical pulse trains

Abstract

A method for measuring a temporal waveform of the electric field of an optical signal avoids substantial sacrifice of sensitivity and enables accurate measuring of the ultra-fast temporal waveform of the electric field of the optical signal. It generates phase conjugated light by applying light whose phase is fixed with respect to optical signal to be measured; obtains spectral phase by observing mixed spectrum generated by combining the optical signal to be measured with the phase conjugated light; and obtains the temporal waveform of the electric field of the optical signal by attaching the spectral phase to a separately observed spectrum of the optical signal to be measured.

Claims

1. A method for measuring a temporal waveform of the electric field of an optical signal comprising the steps of:

generating phase conjugated light by applying local oscillator light to optical signal to be measured;

generating mixed light by combining the optical signal to be measured with the phase conjugated light;

obtaining a spectral phase by observing a spectrum of the mixed light; and

obtaining a temporal waveform of the electric field of the optical signal to be measured by attaching the spectral phase to a separately observed spectrum of the optical signal to be measured.

2. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 1, further comprising the step of acquiring spectra of two mixed light waves which are associated with the local oscillator light having different wavelengths.

3. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 2, further comprising the step of carrying out for each spectrum of the mixed light waves multiple times of measurements with different fixed relative phases between the local oscillator light and the optical signal to be measured.

4. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 2, further comprising the step of comparing, for each wavelength of the local oscillator light, intensity changes in at least two spectral components in the mixed light resulting from changes in a relative phase between the local oscillator light and the optical signal to be measured, and the step of measuring a relative phase between the at least two spectral components using results of the step of comparing.

5. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 2, further comprising the steps of:

splitting the optical signal to be measured;

generating the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split.

6. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 2, further comprising the steps of:

generating the local oscillator light by launching first optical signal to be measured onto an optical filter; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

7. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 2, further comprising the step of amplifying the local oscillator light.

8. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 1, further comprising the step of carrying out for each spectrum of the mixed light waves multiple times of measurements with different fixed relative phases between the local oscillator light and the optical signal to be measured.

9. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 8, further comprising the steps of:

splitting the optical signal to be measured;

generating the local oscillator light by launching first optical signal,to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split.

10. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 8, further comprising the steps of:

generating the local oscillator light by launching first optical signal to be measured onto an optical filter; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

11. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 8, further comprising the step of amplifying the local oscillator light.

12. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 1, further comprising the step of comparing, for each wavelength of the local oscillator light, intensity changes in at least two spectral components in the mixed light resulting from changes in a relative phase between the local oscillator light and the optical signal to be measured, and the step of measuring a relative phase between the at least two spectral components using results of the step of comparing.

13. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 12, further comprising the steps of:

splitting the optical signal to be measured;

generating the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split.

14. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 12, further comprising the steps of:

generating the local oscillator light by launching first optical signal to be measured onto an optical filter; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

15. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 12, further comprising the step of amplifying the local oscillator light.

16. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 12, wherein the step of comparing intensity changes in at least two spectral components resulting from the changes in the relative phase comprises the steps of:

changing the relative phase in a ramp (linear slope) fashion;

generating, for sinusoidal intensity changes obtained, a signal whose phase is shifted by 90 degrees from a spectral component adopted as a reference;

integrating a product of the intensity changes of the spectral component and intensity changes in another spectral component to obtain a first integral;

integrating a product of the intensity changes of the spectral component and the signal whose phase is shifted by 90 degrees to obtain a second integral; and

obtaining the relative phase between the spectral components from a ratio of the two integrals.

17. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 16, further comprising the steps of:

splitting the optical signal to be measured;

generating the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split.

18. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 16, further comprising the steps of:

generating the local oscillator light by launching first optical signal to be measured onto an optical filter; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

19. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 16, further comprising the step of amplifying the local oscillator light.

20. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 16, wherein an integration interval of the integration is set at an integer multiple of a period of the intensity changes in the spectral component adopted as the reference.

21. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 20, further comprising the steps of:

splitting the optical signal to be measured;

generating the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split.

22. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 20, further comprising the steps of:

generating the local oscillator light by launching first optical signal to be measured onto an optical filter; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

23. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 20, further comprising the step of amplifying the local oscillator light.

24. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 1, further comprising the steps of:

splitting the optical signal to be measured;

generating the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split.

25. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 24, further comprising the step of amplifying the local oscillator light.

26. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 24, further comprising the step of limiting a spectral width of the local oscillator light by inserting an optical filter in at least one of two positions before and after the medium with the second-order optical nonlinear effect to which the first optical signal to be measured is incident.

27. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 26, further comprising the step of amplifying the local oscillator light.

28. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 24, further comprising the step of amplifying the light to be incident to the medium with the second-order optical nonlinear effect to which the first optical signal to be measured is incident, or amplifying, when the optical filter is interposed, the light which is output from the optical filter and is to be incident to the medium.

29. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 28, further comprising the step of amplifying the local oscillator light.

30. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 1, further comprising the steps of:

generating the local oscillator light by launching first optical signal to be measured onto an optical filter; and

generating the phase conjugated light by launching the generated local oscillator light and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

31. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 30, further comprising the step of amplifying the local oscillator light.

32. The method for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 1, further comprising the step of amplifying the local oscillator light.

33. An apparatus for measuring a temporal waveform of the electric field of an optical signal comprising:

local oscillator light generating means for generating local oscillator light from optical signal to be measured;

phase conjugated light generating means for generating phase conjugated light using the local oscillator light;

means for obtaining a spectral phase by observing a spectrum of mixed light generated by combining the optical signal to be measured with the phase conjugated light; and

means for obtaining a temporal waveform of the electric field of the optical signal to be measured by attaching the spectral phase to a separately observed spectrum of the optical signal to be measured.

34. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 33, further comprising means for acquiring spectra of two mixed light waves which are associated with the local oscillator light having different wavelengths.

35. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 34, further comprising means for carrying out for each spectrum of the mixed light waves multiple times of measurements with different relative phases between the local oscillator light and the optical signal to be measured.

36. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 34, further comprising:

means for simultaneously observing intensities of at least two spectral components in the mixed light;

means for changing a relative phase between the local oscillator light and the optical signal to be measured; and

means for measuring a relative phase between the at least two spectral components by comparing intensity changes in the at least two spectral components resulting from the changes in the relative phase.

37. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 34, further comprising a beam splitter for splitting the optical signal to be measured, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split by said beam splitter, and wherein said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split by said beam splitter.

38. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 34, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto an optical filter, and said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

39. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 34, further comprising an optical amplifier for amplifying the local oscillator light.

40. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 33, further comprising means for carrying out for each spectrum of the mixed light waves multiple times of measurements with different relative phases between the local oscillator light and the optical signal to be measured.

41. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 40, further comprising a beam splitter for splitting the optical signal to be measured, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split by said beam splitter, and wherein said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split by said beam splitter.

42. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 40, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto an optical filter, and said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

43. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 40, further comprising an optical amplifier for amplifying the local oscillator light.

44. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 33, further comprising:

means for simultaneously observing intensities of at least two spectral components in the mixed light;

means for changing a relative phase between the local oscillator light and the optical signal to be measured; and

means for measuring a relative phase between the at least two spectral components by comparing intensity changes in the at least two spectral components resulting from the changes in the relative phase.

45. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 44, further comprising a beam splitter for splitting the optical signal to be measured, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split by said beam splitter, and wherein said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split by said beam splitter.

46. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 44, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto an optical filter, and said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

47. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 44, further comprising an optical amplifier for amplifying the local oscillator light.

48. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 44, wherein said means for simultaneously observing intensities of at least two spectral components comprises two monochromators, a photo-detector mounted on each of said monochromators, and a beam splitter for splitting the mixed light into two portions to be supplied to said two monochromators.

49. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 48, further comprising a beam splitter for splitting the optical signal to be measured, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split by said beam splitter, and wherein said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split by said beam splitter.

50. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 48, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto an optical filter, and said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

51. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 48, further comprising an optical amplifier for amplifying the local oscillator light.

52. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 44, wherein said means for simultaneously observing intensities of at least two spectral components comprises a spectrograph equipped with a linear detector array.

53. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 52, further comprising a beam splitter for splitting the optical signal to be measured, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split by said beam splitter, and wherein said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split by said beam splitter.

54. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 52, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto an optical filter, and said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

55. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 52, further comprising an optical amplifier for amplifying the local oscillator light.

56. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 33, further comprising a beam splitter for splitting the optical signal to be measured, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto a medium with a second-order optical nonlinear effect, the first optical signal to be measured being a first portion split by said beam splitter, and wherein said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto another medium with a second-order optical nonlinear effect, the second optical signal to be measured being a second portion split by said beam splitter.

57. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 56, further comprising an optical amplifier for amplifying the local oscillator light.

58. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 56, further comprising an optical filter inserted in at least one of two positions before and after the medium with the second-order optical nonlinear effect to which the first optical signal to be measured is incident, said optical filter being deployed for limiting a spectral width of the local oscillator light.

59. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 58, further comprising an optical amplifier for amplifying the local oscillator light.

60. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 56, further comprising an optical amplifier inserted before the medium with the second-order optical nonlinear effect to which the first optical signal to be measured is incident, or between the optical filter and said medium when said optical filter is interposed.

61. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 60, further comprising an optical amplifier for amplifying the local oscillator light.

62. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 33, wherein said local oscillator light generating means generates the local oscillator light by launching first optical signal to be measured onto an optical filter, and said phase conjugated light generating means generates the phase conjugated light by launching the local oscillator light generated by said local oscillator light generating means and second optical signal to be measured onto a medium with a third-order optical nonlinear effect.

63. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 62, further comprising an optical amplifier for amplifying the local oscillator light.

64. The apparatus for measuring a temporal waveform of the electric field of an optical signal as claimed in claim 33, further comprising an optical amplifier for amplifying the local oscillator light.