Claims
- 1. An optical amplifier system comprising:
a fiber communications link; a fiber Raman amplifier in the fiber communications link; a first Raman pump source coupled to the fiber link to provide co-propagating pump light into the fiber amplifier; and a second Raman pump source coupled to the fiber link, at least one of pump power and pump light output spectrum of the first pump source being adjustable in response to changes in at least one of signal channel loading and Raman pump level of the second Raman pump source.
- 2. The system as recited in claim 1 further comprising a wavelength division multiplexed (WDM) signal transmitter coupled to the fiber to provide a WDM signal propagating through the fiber Raman amplifier, the WDM signal transmitter being controlled by a transmitter controller.
- 3. The system as recited in claim 2 wherein the first Raman pump source is coupled to the fiber to receive a control signal from the transmitter controller indicative of channel loading conditions.
- 4. The system as recited in claim 1 further comprising a pump controller coupled to control the first Raman pump source, and coupled to receive a signal from the fiber communications link indicative of at least one of the signal channel loading and the Raman pump level of the second Raman pump source in the fiber communications link.
- 5. The system as recited in claim 1 wherein the first Raman pump source generates second order Raman pump light.
- 6. The system as recited in claim 1 wherein the first Raman pump source includes a semiconductor laser generating second order Raman pump light.
- 7. The system as recited in claim 6 wherein the semiconductor laser is wavelength stabilized.
- 8. The system as recited in claim 1 wherein the first Raman pump source provides depolarized light to the fiber amplifier.
- 9. A fiber communications system, comprising:
a WDM transmitter; a WDM receiver; a fiber link coupled to the WDM transmitter and the WDM receiver; a fiber Raman amplifier disposed in the fiber communications link; a first Raman pump source coupled to the link to provide co-propagating pump light to the fiber Raman amplifier; and a second Raman pump source coupled to the link, at least one of pump power and pump output spectrum of the first pump source being adjustable in response to changes in at least one of signal channel loading and Raman pump level of the second Raman pump source.
- 10. The system as recited in claim 9 further comprising a pump controller coupled to the first Raman pump source to control the at least one of pump power and pump output spectrum of the first Raman pump source.
- 11. The system as recited in claim 9 further comprising at least one erbium doped fiber amplifier (EDFA) disposed in the fiber link, wherein the pump output spectrum of the first Raman pump source is controlled so as to provide Raman gain in the fiber link having a spectral nonuniformity that at least partially compensates for gain spectral nonuniformity of the EDFA.
- 12. A fiber Raman amplifier, comprising:
an optical fiber, a signal propagating in the optical fiber having a signal wavelength; a first pump laser coupled to the fiber to provide first order Raman pump light into the optical fiber for Raman amplifying the signal; and a second pump laser coupled to the fiber to provide second order Raman pump light into the optical fiber for amplifying the first order Raman pump light, the second pump laser including a semiconductor laser.
- 13. The fiber amplifier as recited in claim 12 wherein the pump light from the second pump laser propagates in the optical fiber in a direction opposite to a propagation direction of the pump light from the first pump laser.
- 14. The fiber amplifier as recited in claim 13 wherein the pump light from the second pump laser co-propagates in the optical fiber with the signal.
- 15. The fiber amplifier as recited in claim 12 further comprising a third pump laser coupled to provide first order Raman pump light into the optical fiber in a direction opposite the propagation direction of the pump light from the first pump laser.
- 16. The fiber amplifier as recited in claim 15 further comprising a fourth pump laser coupled to provide second order Raman pump light into the optical fiber in a direction opposite the propagation direction of the pump light from the third pump laser, wherein the pump light from the second pump laser propagates along the fiber in a direction opposite to the propagation direction of pump light from the first pump laser.
- 17. The fiber amplifier as recited in claim 12 wherein the second pump laser includes at least first and second pump laser elements generating second order Raman pump light, a center wavelength of light generated by the first laser element being different from a center wavelength of light generated by the second laser element.
- 18. The fiber amplifier as recited in claim 17 wherein the center wavelengths of the at least first and second pump laser elements of the second pump laser and the relative intensities of outputs from the at least first and second pump laser elements are selected so as to provide a predetermined Raman gain spectral profile for amplifying the pump light from the first pump laser.
- 19. The fiber amplifier as recited in claim 12 wherein the second order Raman pump light is in a wavelength range that substantially avoids absorption by an OH absorption peak in the optical fiber centered at about 1385 nm.
- 20. The fiber amplifier as recited in claim 19 wherein the second wavelength range has a peak wavelength in the range 1360-1365 nm.
- 21. The fiber amplifier as recited in claim 12 wherein there is substantially no absorption in the optical fiber at 1385 nm due to OH.
- 22. The fiber amplifier as recited in claim 12 wherein a signal noise level obtained when both first order and second order Raman pump light are present is improved by more than 0.5 dB over the signal noise level obtained when only first order Raman light is present.
- 23. The fiber amplifier as recited in claim 12 wherein the semiconductor laser includes a coupling fiber to receive light output from a semiconductor gain element, the coupling fiber including a fiber Bragg grating disposed to reflect light at a selected wavelength range to the semiconductor gain element, the coupling fiber being coupled at an output end to the optical fiber.
- 24. The fiber amplifier as recited in claim 23 wherein the semiconductor laser operates under coherence collapse.
- 25. The fiber amplifier as recited in claim 12 further comprising a depolarizer coupled between the semiconductor laser and the optical fiber to depolarize pump light generated by the semiconductor laser.
- 26. The fiber amplifier as recited in claim 12 wherein the semiconductor laser is tuned to a wavelength so as to increase amplification of the signal in the EDFA L-band.
- 27. The fiber amplifier as recited in claim 12 wherein the second order Raman pump light has a spectrum selected so as to optimize amplification of the signal by the first order pump light.
- 28. An optical communications system, comprising:
a WDM transmitter; a WDM receiver; an optical fiber link coupled to the transmitter and the receiver to carry a WDM signal from the WDM transmitter to the WDM receiver; a first pump laser coupled to the fiber link to provide first order Raman pump light into the optical fiber link for Raman amplifying the WDM signal; and a second pump laser coupled to the fiber link to provide second order Raman pump light into the optical fiber link for amplifying the first order Raman pump light, the second pump laser including a semiconductor laser.
- 29. The system as recited in claim 28 further comprising a pump laser controller having a current controller to generate and control current passing through the semiconductor laser and a temperature controller to control operating temperature of the semiconductor laser.
- 30. The system as recited in claim 28 wherein the second pump laser includes at least two semiconductor lasers generating light at different center wavelengths.
- 31. The system as recited in claim 30 further comprising a controller coupled to control relative intensities of outputs from the at least two semiconductor lasers.
- 32. The system as recited in claim 31 further comprising at least one EDFA disposed along the optical fiber link, and wherein the controller controls the relative intensities of the outputs from the at least two semiconductor lasers so as to provide Raman signal gain having a spectral nonuniformity that at least partially compensates for spectral nonuniformity of signal gain of the at least one EDFA.
- 33. The system as recited in claim 31 wherein at least one of pump power and pump output spectrum of the second pump laser is adjustable in response to changes in at least one of signal channel loading and level of first order Raman pump light in the optical fiber link.
- 34. A fiber amplifier comprising:
an optical fiber for propagating a signal in a signal wavelength range; a first Raman pump source coupled to provide first order Raman pump light into the optical fiber to Raman amplify the signal; and a second Raman pump source coupled to provide second order Raman pump light into the optical fiber to Raman amplify the first order Raman pump light, the second Raman pump source including at least first and second pump laser elements, a center wavelength of light generated by the first laser element being different from a center wavelength of light generated by the second laser element.
- 35. The fiber amplifier as recited in claim 34 wherein the center wavelengths of the at least first and second pump laser elements of the second Raman pump source and the relative intensities of outputs from the at least first and second pump laser elements are selected so as to provide a predetermined Raman gain spectral profile for the first order Raman pump light.
- 36. The fiber amplifier as recited in claim 34 wherein the center wavelengths of the at least first and second pump laser elements of the second Raman pump source and the relative intensities of outputs from the at least first and second pump laser elements are selected so as to provide a spectrally flattened gain spectrum to the signal.
- 37. The fiber amplifier as recited in claim 34 wherein the center wavelengths of the at least first and second pump laser elements of the second Raman pump source and the relative intensities of outputs from the at least first and second pump laser elements are selected so as to provide a spectrally flattened signal noise spectrum.
- 38. The fiber amplifier as recited in claim 34 further comprising an erbium-doped fiber amplifier (EDFA) coupled to the fiber to amplify light propagating in the optical fiber, wherein the center wavelengths of the at least first and second pump laser elements of the second Raman pump source and the relative intensities of outputs from the at least first and second pump laser elements are selected so as to provide Raman signal gain having a spectral gain nonuniformity that at least partially compensates for a spectral gain nonuniformity of the EDFA.
- 39. The fiber amplifier as recited in claim 34 wherein the center wavelengths of light output from the first and second pump laser elements are selected so as to avoid absorption by OH in the optical fiber.
- 40. The fiber amplifier as recited in claim 34 wherein at least one of pump power and pump light output spectrum of the second Raman pump source is adjustable in response to changes in signal channel loading in the optical fiber.
- 41. The fiber amplifier as recited in claim 34 wherein at least one of pump power and pump light output spectrum of the second Raman pump source is adjustable in response to changes in first order Raman pump light in the optical fiber.
- 42. The fiber amplifier as recited in claim 34 wherein the at least first and second pump laser elements are semiconductor laser elements, and the second Raman pump source is configured to provide depolarized pump light.
- 43. The fiber amplifier as recited in claim 42 further comprising at least one depolarizer disposed to depolarize light output from the semiconductor laser elements.
- 44. A fiber Raman amplifier, comprising:
an optical fiber, a signal propagating in the optical fiber having a signal wavelength; a first pump laser coupled to the fiber to provide first order Raman pump light into the optical fiber for Raman amplifying the signal; and a second pump laser coupled to the fiber to provide second order Raman pump light into the optical fiber for amplifying the first order Raman pump light, wherein signal gain due to the second order pump laser is in excess of 1 dB and a signal bit error rate (BER) without the second order Raman pump light for a selected level of signal launch power into the optical fiber is the same as the signal BER in the presence of the second order Raman pump light when the signal launch power is less than the selected level of signal launch power by at least 1.2 dB, the BER being no greater than 10−9.
- 45. The fiber amplifier as recited in claim 44 wherein the pump light from the second pump laser propagates in the optical fiber in a direction opposite to a propagation direction of the pump light from the first pump laser.
- 46. The fiber amplifier as recited in claim 44 further comprising a third pump laser coupled to provide first order Raman pump light into the optical fiber in a direction opposite the propagation direction of pump light from the first pump laser.
- 47. The fiber amplifier as recited in claim 46 further comprising a fourth pump laser coupled to provide second order Raman pump light into the optical fiber in a direction opposite the propagation direction of pump light from the third pump laser, wherein pump light from the second pump laser propagates along the fiber in a direction opposite to the propagation direction of pump light from the first pump laser.
- 48. The fiber amplifier as recited in claim 44 wherein the second pump laser includes at least first and second pump laser elements generating second order Raman pump light, a center wavelength of light generated by the first laser element being different from a center wavelength of light generated by the second laser element.
- 49. The fiber amplifier as recited in claim 48 wherein the center wavelengths of the at least first and second pump laser elements of the second pump laser and the relative intensities of outputs from the at least first and second pump laser elements are selected so as to provide a predetermined Raman gain spectral profile for amplifying the pump light from the first pump laser.
- 50. The fiber amplifier as recited in claim 44 wherein the second order Raman pump light is in a wavelength range that substantially avoids absorption by an OH absorption peak in the optical fiber centered at about 1385 nm.
- 51. The fiber amplifier as recited in claim 50 wherein the second wavelength range has a peak wavelength in the range 1360-1365 nm.
- 52. The fiber amplifier as recited in claim 44 wherein there is substantially no absorption in the optical fiber at 1385 nm due to OH.
- 53. The fiber amplifier as recited in claim 44 wherein the second pump laser is a semiconductor laser.
- 54. The fiber amplifier as recited in claim 53 wherein the semiconductor laser includes a coupling fiber to receive light output from a semiconductor gain element, the coupling fiber including a fiber Bragg grating disposed to reflect light at a selected wavelength range to the semiconductor gain element, the coupling fiber being coupled at an output end to the optical fiber.
- 55. The fiber amplifier as recited in claim 53 wherein the semiconductor laser operates under coherence collapse.
- 56. The fiber amplifier as recited in claim 44 further comprising an optical device disposed between the second pump laser and the optical fiber to prevent first order Raman pump light from reaching the second pump laser from the optical fiber.
- 57. The fiber amplifier as recited in claim 56 wherein the optical device is an optical isolator.
- 58. The fiber amplifier as recited in claim 56 wherein the optical device is a WDM coupler disposed to couple light from the second pump laser into the optical fiber.
- 59. The fiber amplifier as recited in claim 56 further comprising a coupling fiber disposed between the second pump laser and the optical fiber, the coupling fiber including a fiber Bragg grating having a high reflectivity for first order Raman pump light.
- 60. The fiber amplifier as recited in claim 44 wherein the second pump laser provides depolarized pump light to the optical fiber.
- 61. The fiber amplifier as recited in claim 44 further comprising a depolarizer coupled between the second pump laser and the optical fiber to depolarize pump light generated by the second pump laser.
- 62. The fiber amplifier as recited in claim 44 wherein the second pump laser is tuned to a wavelength so as to increase amplification of the signal in the EDFA L-band.
- 63. The fiber amplifier as recited in claim 44 wherein the second order Raman pump light has a spectrum selected so as to optimize amplification of the signal by the first order pump light.
- 64. An optical communications system, comprising:
a WDM transmitter; a WDM receiver; an optical fiber link coupled to carry a WDM signal from the WDM transmitter to the WDM receiver; a first pump laser coupled to the fiber link to provide first order Raman pump light into the optical fiber link for Raman amplifying the WDM signal; and a second pump laser coupled to the fiber link to provide second order Raman pump light into the optical fiber link for amplifying the first order Raman pump light, wherein WDM signal gain due to the second order pump laser is in excess of 1 dB and a WDM signal bit error rate (BER) without the second order Raman pump light for a selected level of WDM signal launch power into the optical fiber is the same as the WDM signal BER in the presence of the second order Raman pump light when the WDM signal launch power is less than the selected level of WDM signal launch power by at least 1.2 dB, the BER being no greater than 10−9.
- 65. The system as recited in claim 64 further comprising a second pump laser controller coupled to the second pump laser to control operation of the second pump laser.
- 66. The system as recited in claim 64 wherein the second pump laser includes at least two lasers generating light at different center wavelengths.
- 67. A system as recited in claim 66 further comprising a controller coupled to control the relative intensities of outputs from the at least two lasers.
- 68. A system as recited in claim 67 further comprising at least one EDFA disposed along the optical fiber link, wherein the controller controls the relative intensities of the outputs from the at least two semiconductor lasers so as to provide Raman signal gain having a spectral nonuniformity that at least partially compensates for spectral nonuniformity of signal gain of the at least one EDFA.
- 69. The system as recited in claim 67 wherein at least one of pump power and pump output spectrum of the second pump laser is adjustable by the controller in response to changes in at least one of signal channel loading and level of first order Raman pump light in the optical fiber link.
- 70. A fiber Raman amplifier comprising:
an optical fiber, a signal propagating in the optical fiber having a signal wavelength; a first pump source coupled to the optical fiber to provide first order Raman pump light into the optical fiber for Raman amplifying the signal; a second pump source coupled to the optical fiber to provide second order Raman pump light into the optical fiber for amplifying the first order Raman pump light; and a third pump source coupled to the optical fiber to provide third order Raman pump light into the optical fiber for amplifying the second order Raman pump light.
- 71. The amplifier as recited in claim 70 wherein one of the second and third pump sources includes a semiconductor laser.
- 72. The amplifier as recited in claim 70 wherein the third order pump light co-propagates along the fiber with the second order pump light.
- 73. The amplifier as recited in claim 70 wherein the second order pump light co-propagates along the fiber with the first order pump light.
- 74. The amplifier as recited in claim 70 wherein the third order pump source includes first and second light sources generating light centered at respective first and second center wavelengths, the first center wavelength being different from the second center wavelength.
- 75. The amplifier as recited in claim 70 wherein the third order pump source provides depolarized pump light to the optical fiber.
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional Application No. 60/224,108, entitled Second Order Raman Pumping Architectures, filed Aug. 9, 2000 and U.S. Provisional Application No. 60/257,701, entitled Second Order Fiber Raman Amplifiers, filed Dec. 21, 2000.
Provisional Applications (2)
|
Number |
Date |
Country |
|
60224108 |
Aug 2000 |
US |
|
60257701 |
Dec 2000 |
US |