Optical communication system compensating for chromatic dispersion and phase conjugate light generator for use therewith

• US 5,798,853 A
• Filed: 12/16/1996
• Issued: 08/25/1998
• Est. Priority Date: 10/16/1992
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Watanabe, Shigeki
• Primary Examiner(s): Williams, Hezrone E.
• Assistant Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US08/766,052
• Time in Patent Office: 617 Days
• Field of Search: 385/1, 385/5, 385/122, 359/326, 359/300, 359/238, 359/240, 359/160, 359/161, 372/21
• US Class Current: 398/150
• CPC Class Codes: G02F 1/3538 for optical phase conjugation controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation using optical phase conjugation H01S3/10076
• CPC Class Codes: H04B 10/2531 using spectral inversion

Abstract

An optical communication system compensating for chromatic dispersion and a phase conjugate light generator for use therewith. The system includes an optical transmitter which receives an input signal and transmits signal light over an optical transmission line which is then input to a phase conjugate light generation unit. The phase conjugate light generation unit generates phase conjugate light corresponding to the signal light and outputs the phase conjugate light to an optical receiver which reproduces a demodulated signal corresponding to the input signal. The system compensates for chromatic dispersion by having the phase conjugate light generator generate phase conjugate light corresponding to signal light received over a first optical transmission line and then transmitting the generated phase conjugate light over a second optical transmission line.

Claims

1. A phase conjugate light generator, comprising:

an optical fiber providing a zero-dispersion at a first wavelength, the optical fiber having first and second ends;

a signal supply for supplying to the first end of the optical fiber an optical signal having an original phase; and

a light source for outputting to the first end of the optical fiber a pumping light having a wavelength substantially equal to the first wavelength such that the phase of light travelling in the optical fiber is changed from the original phase and a phase conjugate light having a phase which is a conjugate of the original phase is emitted from the second end of the optical fiber.

2. A phase conjugate light generator according to claim 1, wherein the optical signal has wavelength which is different from the first wavelength.

3. A phase conjugate light generator according to claim 1, wherein the optical fiber is a single mode optical fiber.

4. A phase conjugate light generator according to claim 1, wherein the optical fiber provides a third order non-linear optical effect and generates the phase conjugate light through four-wave mixing.

5. A phase conjugate light generator according to claim 1, further comprising an optical band pass filter downstream from the second end of the optical fiber so that the phase conjugate light passes through the optical band pass filter.

6. A phase conjugate light generator according to claim 1, further comprising an optical amplifier downstream from the second end of the optical fiber, for amplifying the phase conjugate light.

7. A phase conjugate light generator according to claim 1, wherein the optical signal is composed of a plurality of signal light components multiplexed by frequency division multiplexing.

8. An optical communication system comprising:

a first single mode optical fiber transmission line for transmitting a first optical signal having an original phase;

a second single mode optical fiber transmission line; and

an optical chromatic dispersion compensation device, comprising;

an optical fiber providing a zero-dispersion at a first wavelength, the optical fiber having first and second ends;

a first terminal for receiving the first optical signal from the first single mode optical fiber transmission line and for inputting the first optical signal to the first end of the optical fiber;

a light source for outputting to the first end of the optical fiber a pumping light having a wavelength substantially equal to the first wavelength such that the phase of light travelling in the optical fiber is changed from the original phase and a phase conjugate light having a phase which is a conjugate of the original phase is emitted from the second end of the optical fiber; and

a second terminal for receiving from the second end of the optical fiber the phase conjugate light emitted from the second end of the optical fiber, the second terminal being coupled to the second signal mode optical fiber transmission line for outputting the phase conjugate light to the second single mode optical fiber transmission line for travel through the second single mode optical fiber transmission line.

9. An optical communication system according to claim 8, wherein the first and second single mode optical transmission lines have chromatic dispersion values which are substantially the same.

10. A phase conjugate light generator, comprising:

a non-linear optical medium;

a splitter for splitting an optical signal having an original phase into a first polarized component having a first polarization plane and a second polarized component having a second polarization plane perpendicular to the first polarization plane and supplying the first and second polarized components to the non-linear optical medium; and

a light source for outputting to the non-linear optical medium a pumping light having a polarization plane substantially the same as one of the first and second polarization planes such that a phase conjugate light having a phase which is a conjugate of the original phase is generated in the non-linear optical medium.

11. A phase conjugate light generator according to claim 10, wherein the light source outputs first and second pumping light beams respectively having substantially the same polarization planes as the first and second polarization planes.

12. A phase conjugate light generator according to claim 10, wherein the non-linear optical medium comprises an optical fiber.

13. A phase conjugate light generator, comprising:

first and second non-linear optical mediums;

a splitter for splitting an optical signal having an original phase into a first polarized component having a first polarization plane and a second polarized component having a second polarization plane perpendicular to the first polarization plane and supplying the first and second polarized components respectively to the first and second non-linear optical mediums; and

a light source for outputting to the first and second non-linear optical mediums first and second pumping light beams respectively having substantially the same polarization planes as the first and second polarization planes such that the optical signal is transformed in the first and second non-linear optical mediums and first and second phase conjugate light beams are respectively generated in the first and second non-linear optical mediums, the first and second phase conjugate light beams having a phase which is a conjugate of the original phase.

14. A phase conjugate light generator, comprising:

an optical fiber having first and second ends;

a splitter for splitting an optical signal having an original phase into a first polarized component having a first polarization plane and a second polarized component having a second polarization plane perpendicular to the first polarization plane and supplying the first and second polarized components respectively to the first and second ends of the optical fiber; and

a light source for outputting to the first and second ends of the optical fiber first and second pumping light beams respectively having substantially the same polarization planes as the first and second polarization planes such that the first and second polarized components are transformed in the optical fiber into first and second phase conjugate light beams which are emitted from the second and first ends of the optical fiber, respectively, the first and second phase conjugate light beams having a phase which is a conjugate of the original phase.

15. A phase conjugate light generator according to claim 14, further comprising a polarized light controller provided on the optical fiber for maintaining the respective polarization planes of the first and second polarized components and the first and second pumping light beams travelling in the optical fiber.

16. A phase conjugate light generator according to claim 14, wherein the optical fiber is a polarization maintaining optical fiber.

17. A phase conjugate light generator, comprising:

a non-linear optical medium;

a signal supply for supplying to the non-linear optical medium an optical signal having an original phase; and

a light source for outputting to the non-linear optical medium a pumping light having a polarization which is scrambled such that the optical signal is transformed in the non-linear optical medium and a phase conjugate light is generated in the non-linear optical medium, the phase conjugate light having a phase which is a conjugate of the original phase.

18. A phase conjugate light generator, comprising:

a non-linear optical medium;

a signal supply for supplying to the non-linear optical medium an optical signal saving a polarization which is scrambled and having an original phase; and

a light source for outputting to the non-linear optical medium a pumping light such that the optical signal is transformed in the non-linear optical medium and a phase conjugate light is generated in the non-linear optical medium, the phase conjugate light having a phase which is a conjugate of the original phase.

19. An optical communication system, comprising:

a first optical fiber transmission line for transmitting an optical signal having an original phase;

a phase conjugate light generator for receiving the optical signal from the first optical fiber transmission line, transforming the optical signal and generating a phase conjugate light having a phase which is a conjugate of the original phase; and

a second optical fiber transmission line for receiving the phase conjugate light from the phase conjugate light generator and transmitting the phase conjugate light, the first and second optical fiber transmission lines being selected so that the optical Kerr effect in the first optical fiber transmission line is substantially equal to the optical Kerr effect in the second optical fiber transmission line.

20. An optical communication system according to claim 19, wherein the first and second optical fiber transmission lines satisfy the following equation:

##EQU22## where ω

_s and ω

_c represent the optical frequencies of the optical signal and the phase conjugate light respectively, n₂₁ and n₂₂ represent the non-linear refractive indices of the first and second optical fiber transmission lines respectively, L₁ and L₂ represent the fiber lengths of the first and second optical fiber transmission lines respectively, A_eff1 and A_eff2 represent the effective core areas of the first and second optical fiber transmission lines respectively, and P_s and P_c represent the mean powers of the optical signal and the phase conjugate light respectively.

21. An optical communication system according to claim 20, wherein the first and second optical fiber transmission lines are selected so that the optical frequencies ω

_s and ω

_c, the non-linear refractive indices n₂₁ and n₂₂, the fiber lengths L₁ and L₂, the effective core areas A_eff1 and A_eff2 and the mean powers P_s and P_c optimize compensation for chromatic dispersion.

22. An optical communication system according to claim 19, further comprising:

an optical transmitter, optically connected to the first optical fiber transmission line, for modulating the optical signal in accordance with an input signal; and

an optical receiver, optically connected to the second optical fiber transmission line, for demodulating the phase conjugate light and producing a demodulated signal corresponding to the input signal.

23. An optical communication system according to claim 22, wherein the optical receiver includes a photo detector for converting the phase conjugate light into an electrical signal.

24. An optical communication system according to claim 22, wherein the optical receiver includes a local light source for outputting a local light to be coupled with the phase conjugate light, and a photo detector for converting the phase conjugate light and the local light into an electrical signal.

25. An optical communication system according to claim 19, further comprising:

an optical amplifier for amplifying the optical signal; and

an optical band pass filter located downstream from the optical amplifier and upstream from the phase conjugate light generator for filtering the optical signal amplified by the optical amplifier before the optical signal reaches the phase conjugate generator.

26. An optical communication system according to claim 19, wherein:

the first and second optical fiber transmission lines have initial portions, the optical signal and the phase conjugate light have respective mean peak intensities, and

the mean peak intensities are substantially the same in the initial portions of the first and second optical fiber transmission lines.

27. An optical communication system according to claim 19, wherein:

the optical signal and the phase conjugate light have intensity distributions respectively in longitudinal directions of the first and second optical fiber transmission lines, and

the intensity distributions of the optical signal and the phase conjugate light are substantially symmetrical.

28. An optical communication system according to claim 27, further comprising a plurality of optical amplifiers provided along the second optical fiber transmission line for amplifying the phase conjugate light transmitted on the second optical fiber transmission line.

29. A phase conjugate light generator, comprising:

a first optical fiber transmission line for transmitting an optical signal having an original phase;

a phase conjugate light generator comprising;

a non-linear optical medium connected to the first optical fiber transmission line to receive the optical signal, and

a light source for outputting to the non-linear optical medium a pumping light so that the optical signal is transformed in the non-linear optical medium and a phase conjugate light is generated in the non-linear optical medium, the phase conjugate light having phase which is a conjugate of the original phase,

a second optical fiber transmission line for receiving the phase conjugate light from the phase conjugate light generator and transmitting the phase conjugate light, the first and second optical fiber transmission lines being selected so that the optical Kerr effect in the first optical fiber transmission line is substantially equal to the optical Kerr effect in the second optical fiber transmission line.

30. A phase conjugate light generator according to claim 29, wherein the first and second optical fiber transmission lines are selected to approximately satisfy the following equation:

##EQU23## where ω

_s and ω

_c represent the optical frequencies of the optical signal and the phase conjugate light respectively, n₂₁ and n₂₂ represent the non-linear refractive indices of the first and second optical fiber transmission lines respectively, L₁ and L₂ represent the fiber lengths of the first and second optical fiber transmission lines respectively, A_eff1 and A_eff2 represent the effective core areas of the first and second optical fiber transmission lines respectively, and P_s and P_c represent the mean powers of the optical signal and the phase conjugate light respectively.

31. A phase conjugate light generator according to claim 30, wherein the first and second optical fiber transmission lines are selected so that the optical frequencies ω

_s and ω

_c, the non-linear refractive indices n₂₁ and n₂₂, the fiber lengths L₁ and L₂, the effective core areas A_eff1 and A_eff2 and the mean powers P_s and P_c optimize compensation for chromatic dispersion.

32. A phase conjugate light generator according to claim 29, wherein the second optical fiber transmission line acts as an optical compensation device.

33. An optical compensation apparatus, optically connected to a first optical fiber transmission line for receiving an optical signal having an original phase from the first optical fiber transmission line, comprising:

a phase conjugate light generator for receiving the optical signal, transforming the optical signal and generating a phase conjugate light having a phase which is a conjugate of the original phase; and

a second optical fiber transmission line for receiving the phase conjugate light from the phase conjugate light generator and transmitting the phase conjugate light, the second optical fiber transmission line being selected so that the optical Kerr effect in the second optical fiber transmission line is substantially equal to the optical Kerr effect in the first optical fiber transmission line.

34. An optical compensation apparatus according to claim 33, wherein the first and second optical fiber transmission lines satisfy the following equation:

##EQU24## where ω

_s and ω

_c represent the optical frequencies of the optical signal and the phase conjugate light respectively, n₂₁ and n₂₂ represent the non-linear refractive indices of the first and second optical fiber transmission lines respectively, L₁ and L₂ represent the fiber lengths of the first and second optical fiber transmission lines respectively, A_eff1 and A_eff2 represent the effective core areas of the first and second optical fiber transmission lines respectively, and P_s and P_c represent the mean powers of the optical signal and the phase conjugate light respectively.

35. An optical compensation apparatus according to claim 34, wherein the second optical fiber transmission line is selected so that the optical frequencies ω

_s and ω

_c, the non-linear refractive indices n₂₁ and n₂₂, the fiber lengths L₁ and L₂, the effective core areas A_eff1 and A_eff2 and the mean powers P_s and P_c optimize compensation for chromatic dispersion.

36. An optical compensation apparatus for supplying a phase conjugate light to a second optical fiber transmission line, comprising:

a first optical fiber transmission line for transmitting an optical signal having an original phase, the first optical fiber transmission line being selected so that the optical Kerr effect in the first optical fiber transmission line is substantially equal to the optical Kerr effect in the second optical fiber transmission line;

a phase conjugate light generator for receiving the optical signal from the first optical fiber transmission line, transforming the optical signal and generating the phase conjugate light, the phase conjugate light having a phase which is a conjugate of the original phase.

37. An optical compensation apparatus according to claim 36, wherein the first and second optical fiber transmission lines satisfy the following equation:

##EQU25## where ω

_s and ω

_c represent the optical frequencies of the optical signal and the phase conjugate light respectively, n₂₁ and n₂₂ represent the non-linear refractive indices of the first and second optical fiber transmission lines respectively, L₁ and L₂ represent the fiber lengths of the first and second optical fiber transmission lines respectively, A_eff1 and A_eff2 represent the effective core areas of the first and second optical fiber transmission lines respectively, and P_s and P_c represent the mean powers of the optical signal and the phase conjugate light respectively.

38. An optical compensation apparatus according to claim 37, wherein the first optical fiber transmission line is selected so that the optical frequencies ω

_s and ω

_c, the non-linear refractive indices n₂₁ and n₂₂, the fiber lengths L₁ and L₂, the effective core areas A_eff1 and A_eff2 and the mean powers P_s and P_c optimize compensation for chromatic dispersion.

39. A phase conjugate light generator, comprising:

a non-linear optical medium;

a signal supply for supplying to the non-linear optical medium an optical signal having an original phase and comprising a first optical signal pulse train; and

a light source for outputting to the non-linear optical medium a pumping light pulse train synchronized with the first optical signal pulse train such that the optical signal is transformed in the non-linear optical medium and a phase conjugate light is generated in the non-linear optical medium, the phase conjugate light having a phase which is a conjugate of the original phase, the phase conjugate light comprising a second optical signal pulse train synchronized with the first optical signal pulse train and the pumping light pulse train.

40. An optical compensation apparatus, comprising:

a non-linear optical medium;

a signal supply for supplying to the non-linear optical medium an optical signal having an original phase and comprising a first optical signal pulse train; and

a light source for outputting to the non-linear optical medium a pumping light pulse train having a pumping pulse width, the pumping light pulse train being synchronized with the optical signal pulse train such that the optical signal is transformed in the non-linear optical medium and a phase conjugate light is generated in the non-linear optical medium, the phase conjugate light having a phase which is a conjugate of the original phase, the phase conjugate light comprising a second optical signal pulse train synchronized with the first optical signal pulse train and the pumping light pulse train, the second optical signal pulse train having a pulse width and the pumping pulse width being selected to control the pulse width of the second optical signal pulse train.

42. An optical communication system according to claim 40, wherein the pumping light pulse train has a narrower pulse width than the first optical signal pulse train whereby the second optical signal pulse train is effectively reshaped.

41. An optical communication system, comprising:

a first optical fiber transmission line for transmitting an optical signal having an original phase and comprising a first optical signal pulse train; and

an optical compensation device including;

a non-linear optical medium connected to the first optical fiber transmission line to receive the optical signal;

a light source for outputting to the non-linear optical medium a pumping light pulse train synchronized with the first optical signal pulse train such that the optical signal is transformed in the non-linear optical medium and a phase conjugate light is generated in the non-linear optical medium, the phase conjugate light having a phase which is a conjugate of the original phase, the phase conjugate light comprising a second optical signal pulse train synchronized with the first optical signal pulse train and the pumping light pulse train; and

a second optical fiber transmission line for receiving the phase conjugate light from the non-linear optical medium and for transmitting the phase conjugate light.

43. An optical communication system according to claim 41, wherein the pumping pulse train is in a Return to Zero signal encoding format.

44. An optical communication system according to claim 43, wherein the first optical signal pulse train is in a Non Return to Zero signal encoding format.

45. An optical communication system according to claim 43, wherein the first optical signal pulse train is in a Return to Zero signal encoding format.

46. An optical communication system according to claim 43, wherein the first optical signal pulse train comprises a soliton pulse train.

47. An optical communication system according to claim 41, wherein the pumping light pulse train comprises a soliton pulse train.

48. A phase conjugate light generator, comprising:

an optical fiber having first and second ends;

a signal supply for supplying to the first end of the optical fiber an optical signal having an original phase;

a light source for outputting to the first end of the optical fiber a pumping light modulated by a low frequency such that the phase of light travelling in the optical fiber is changed from the original phase and phase conjugate light have a phase which is a conjugate of the original phase is emitted from the second end of the optical fiber.

49. A phase conjugate light generator according to claim 48, wherein the optical fiber provides a zero dispersion at a first wavelength, and the pumping light has a wavelength substantially equal to the first wavelength.

50. A phase conjugate light generator according to claim 48, wherein the low frequency signal used for modulating the pumping light has a frequency in the range of from 10 kHz to 1 MHz.