Control apparatus and method for optical amplifier, optical amplifier, optical transmission apparatus, individual band gain equalizer, wavelength multiplexing transmission apparatus, optical amplifier and wavelength multiplexing transmission system using the same equalizer

• US 20060203329A1
• Filed: 02/28/2006
• Published: 09/14/2006
• Est. Priority Date: 03/14/2005
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Onaka, Miki, Hayashi, Etsuko, Muro, Shinichirou, Nishihara, Masato
• Granted Patent: US 7,359,112 B2
• Time in Patent Office: Days
• US Class Current: 359/337
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/10015 by monitoring or controlling, e.g. attenuating, the input signal
• CPC Class Codes: H01S 3/10069 Memorized or pre-programmed characteristics, e.g. look-up table [LUT]
• CPC Class Codes: H01S 3/13013 by controlling the optical pumping
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 3/302 in an optical fibre
• CPC Class Codes: H04B 10/2942 using automatic gain control [AGC] H04B10/296 takes precedence

Abstract

A control apparatus comprises a light monitoring unit for dividing a signal wavelength band into at least a band in which output light power of an optical amplifier tends to decrease at an decrease in the number of signal wavelengths and a band including a gain deviation band, and for monitoring inputted light power for the individual divided bands, a calculation unit for obtaining the number of signal wavelengths in the individual divided bands based on a monitor result, and a target gain correction unit for correcting a target gain based on a result of the calculation. This suppresses a transient variation of signal light level due to SHB or SRS at a high speed with a simple configuration without deteriorating noise characteristic, thus enabling optical amplifiers to be further disposed in a multi-stage fashion, which can lengthen the transmission distance of a transmission system including an optical add/drop unit.

Claims

1. A control apparatus for an optical amplifier comprising:

an automatic gain control unit for controlling a gain of said optical amplifier to a constant value based on power of incoming light and outgoing light of said optical amplifier and a target gain;

an individual band incoming light monitoring unit for dividing a signal wavelength band of the incoming light into at least a first band and second band;

said first band has tendency of decreasing power of the outgoing light at an decrease in the number of signal wavelengths and said second band, is a signal wavelength band other than said first band and, including a gain deviation band in which power of the outgoing light varies mainly due to a wavelength deviation of the gain control by said automatic gain control unit, and for monitoring power of the incoming light to said optical amplifier in each of the first and second bands;

an individual band signal wavelength number calculation unit for obtaining the number of signal wavelengths in each of the first and second bands based on a result of the monitoring by the individual band incoming light monitoring unit; and

a target gain correction unit for correcting said target gain to be used in said automatic gain control unit based on a result of the calculation by said individual band signal wavelength number calculation unit at a variation of the number of signal wavelengths.

2. The control apparatus according to claim 1, wherein said individual band incoming light monitoring unit divides said signal wavelength band into three bands:

an SHB band, said gain deviation band and SRS band, said SHB band being under dominance of a spectral hole burning (SHB) effect as said first band, and said SRS band being under dominance of a stimulated Raman scattering (SRS) effect occurring in an output transmission line of said optical amplifier as another band of said first band, and monitors power of the incoming light in each of said three bands.

3. The control apparatus according to claim 2, wherein said signal wavelength band is a C band, and said SHB band is from 1530 nm to 1540 nm, said SRS band is from 1555 nm to 1565 nm, and said gain deviation band is a band interposed between said SHB band and said SRS band.

4. The control apparatus according to claim 1, wherein said individual band signal wavelength number calculation unit divides values of power monitored for the individual divided bands by said individual band incoming light monitoring unit by a design value of power of signal light per signal wavelength, and determines a value closest to the nth power of 2 from the resultant value obtained by the division as the number of signal wavelengths in each of the divided bands.

5. The control apparatus according to claim 4, wherein a threshold to be used for the determination of the number of signal wavelengths is set on the basis of a characteristic of output light power variation in each of the divided bands.

6. The control apparatus according to claim 5, wherein said threshold for said first band is set to be smaller than a threshold for said second band including said gain deviation band.

7. The control apparatus according to claim 1, wherein said target gain correction unit increases said target gain, when recognizing, based on a result of the calculation by said individual band signal wavelength number calculation unit, that the number of signal wavelengths in said first band becomes smaller than a predetermined value.

8. The control apparatus according to claim 1, wherein said target gain correction unit decreases said target gain, when recognizing, based on a result of the calculation by said individual band signal wavelength number calculation unit, that the number of signal wavelengths in said gain deviation band becomes smaller than a predetermined value, in a state where the remaining number of signal wavelengths in said first band exceeds a predetermined value.

9. The control apparatus according to claim 1, wherein said target gain correction unit updates said target gain based on a result of the calculation by said individual band signal wavelength number calculation unit until a predetermined period of time elapses from the occurrence of a variation of the number of signal wavelengths and, after the elapse of said predeterminded period of time, brings said target gain gradually closer to a specified gain value.

10. A control method for an optical amplifier having an automatic gain control function to control a gain of said optical amplifier to a constant value based on power of incoming light and outgoing light of said optical amplifier and a target gain, comprising the steps of:

dividing a signal wavelength band of the incoming light into at least a first band and second band;

said first band has tendency of decreasing power of the outgoing light at a decrease in the number of signal wavelengths and said second band, is a signal wavelength band other than said band, including a gain deviation band in which power of the outgoing light varies mainly due to a wavelength deviation of the gain control, and monitoring power of the incoming light in each of the divided bands;

obtaining the number of signal wavelengths in each of the divided bands based on a result of the monitoring; and

correcting said target gain to be used for the automatic gain control based on the number of signal wavelengths in each of the divided bands at a variation of the number of signal wavelengths.

11. The control method according to claim 10, comprising:

dividing said incoming light signal wavelength band into three bands;

an SHB band, said gain deviation band and an SRS band, said SHB band being under dominance of a spectral hole burning (SHB) effect as said first band, and said SRS band being under dominance of a stimulated Raman scattering (SRS) effect occurring in an output transmission line of said optical amplifier as another band of said first band, and

monitoring power of incoming light in each of said three bands.

12. The control method according to claim 11, wherein said signal wavelength band is a C band, and said SHB band is from 1530 nm to 1540 nm, said SRS band is from 1555 nm to 1565 nm, and said gain deviation band is a band interposed between said SHB band and said SRS band.

13. The control method according to claim 10, comprising:

dividing values of power monitored for the individual divided bands by a design value of power of signal light per signal wavelength, and

determining a value closest to the nth power of 2 from the resultant value obtained by the division as the number of signal wavelengths in each of the divided bands.

14. The control method according to claim 13, wherein a threshold to be used for the determination of the number of signal wavelengths is set on the basis of a characteristic of output light power variation in each of the divided bands.

15. The control method according to claim 14, wherein said threshold for said first band is set to be smaller than a threshold for said second band including said gain deviation band.

16. The control method according to claim 10, wherein said target gain is increased when the number of signal wavelengths in said first band becomes smaller than a predetermined value.

17. The control method according to claim 10, wherein said target gain is decreased when the number of signal wavelengths in said gain deviation band becomes smaller than a predetermined value, in a state where the remaining number of signal wavelengths in said first band exceeds a predetermined value.

18. The control method according to claim 10, wherein said target gain is updated based on the number of signal wavelengths for each of the divided bands until a predetermined period of time elapses from the occurrence of a variation of the number of signal wavelengths and, after the elapse of said predetermined period of time, said target gain is brought gradually closer to a specified gain value.

19. An optical transmission apparatus comprising:

an automatic gain control unit for controlling a gain of an optical amplifier to a constant value based on power of incoming light and outgoing light of said optical amplifier and a target gain;

an individual band incoming light monitoring unit for dividing a signal wavelength band of the incoming light into at least a first band and second band;

said first band has tendency of decreasing power of the outgoing light per channel at a decrease in the number of signal wavelengths or increasing power of the outgoing light per channel at an increase in the number of signal wavelengths and asid second band, is a signal wavelength band other than said band, including a gain deviation band in which power of the outgoing light per channel varies mainly due to a wavelength deviation of the gain control by said automatic gain control unit, and for monitoring power of the incoming light in each of the divided bands;

an individual band signal wavelength number calculation unit for obtaining the number of signal wavelengths in each of the divided bands based on a result of the monitoring by said individual band incoming light monitoring unit; and

a target gain correction unit for correcting said target gain to be used by said automatic gain control unit based on a result of the calculation by said individual band signal wavelength number calculation unit at a variation of the number of signal wavelengths.

20. The optical transmission apparatus according to claim 19, wherein said individual band input light monitoring unit divides said signal wavelength band into three bands:

an SHB band, said gain deviation band and an SRS band, said SHB band being under dominance of a spectral hole burning (SHB) effect as said first band and said SRS band being under dominance of a stimulated Raman scattering (SRS) effect occurring in an output transmission line of said optical amplifier as another band of said first band , and monitors power of the incoming light in each of said three bands.

21. The optical transmission apparatus according to claim 20, wherein said SHB band is from 1530 nm to 1540 nm, said SRS band is from 1555 nm to 1565 nm, and said gain deviation band is a band interposed between said SHB band and said SRS band.

22. The optical transmission apparatus according to claim 19, wherein said individual band signal wavelength number calculation unit divides values of power monitored for the individual divided bands by said individual band incoming light monitoring unit by a design value of power of signal light per signal wavelength, and determines a value closest to the nth power of 2 from the resultant value obtained by the division as the number of signal wavelengths in each of the divided bands.

23. The optical transmission apparatus according to claim 22, wherein a threshold to be used for the determination of the number of signal wavelengths is set on the basis of a characteristic of output light power variation per channel in each of the divided bands.

24. The optical transmission apparatus according to claim 23, wherein said threshold for said first band is set to be smaller than a threshold for said second band including said gain deviation band.

25. The optical transmission apparatus according to claim 19, wherein said target gain correction unit increases said target gain, when recognizing, based on a result of the calculation by said individual band signal wavelength number calculation unit, that the number of signal wavelengths in said first band becomes smaller than a predetermined value.

26. The optical transmission apparatus according to claim 19, wherein said target gain correction unit decreases said target gain, when recognizing, based on a result of the calculation by said individual band signal wavelength number calculation unit, that the number of signal wavelengths in said gain deviation band becomes smaller than a predetermined value, in a state where the remaining number of signal wavelengths in said first band exceeds a predetermined value.

27. The optical transmission apparatus according to claim 19, wherein said target gain correction unit updates said target gain based on a result of the calculation by said individual band signal wavelength number calculation unit until a predetermined period of time elapses from the occurrence of a variation of the number of signal wavelengths and, after the elapse of said predetermined period of time, brings said target gain gradually closer to a specified gain value.

28. An optical amplifier having an automatic gain control function to control a gain to a constant value based on power of incoming light and outgoing light and a target gain, comprising:

dividing a signal wavelength band of the incoming light into at least a first band and second band;

said first band has tendency of decreasing power of the outgoing light per channel at a decrease in the number of signal wavelengths or increasing power of the outgoing light per channel at an increase in the number of signal wavelengths and said second band, is a signal wavelength band other than said band, including a gain deviation band in which power of the outgoing light varies mainly due to a wavelength deviation of the gain control;

monitoring power of the incoming light in each of the divided bands;

obtaining the number of signal wavelengths in each of the divided bands based on a result of the monitoring; and

correcting said target gain to be used for the automatic gain control based on the number of signal wavelengths in each of the divided bands at a variation of the number of signal wavelengths.

29. The optical amplifier according to claim 28, comprising:

dividing said signal wavelength band into three bands;

an SHB band, said gain deviation band and an SRS band, said SHB band being under dominance of a spectral hole burning (SHB) effect as said first band, and said SRS band being under dominance of a stimulated Raman scattering (SRS) effect occurring in an output transmission line of said optical amplifier as another band of said first band; and

monitoring power of incoming light in each of said three bands.

30. The optical amplifier according to claim 29, wherein said SHB band is from 1530 nm to 1540 nm, said SRS band is from 1555 nm to 1565 nm, and said gain deviation band is a band interposed between said SHB band and said SRS band.

31. The optical amplifier according to claim 28, comprising:

dividing values of power monitored for the individual divided bands by a design value of power of signal light per signal wavelength; and

determining a value closest to the nth power of 2 from the resultant value obatained by the division as the number of signal wavelengths in each of the divided bands.

32. The optical amplifier according to claim 31, wherein a threshold to be used for the determination of the number of signal wavelengths is set on the basis of a characteristic of output light power variation per channel in each of the divided bands.

33. The optical amplifier according to claim 32, wherein said threshold for said first band is set to be smaller than a threshold for said second band including said gain deviation band.

34. The optical amplifier according to claim 28, wherein said target gain is increased when the number of signal wavelengths in said first band becomes smaller than a predetermined value.

35. The optical amplifier according to claim 28, wherein said target gain is decreased when the number of signal wavelengths in said gain deviation band becomes smaller than a predetermined value, in a state where the remaining number of signal wavelengths in said first band exceeds a predetermined value.

36. The optical amplifier according to claim 28, wherein said target gain is updated on the basis of the number of signal wavelengths for each of the divided bands until a predetermined period of time elapses from the occurrence of a variation of the number of signal wavelengths and, after the elapse of said predetermined period of time, said target gain is brought gradually closer to a specified gain value.

37. An individual band gain equalizer comprising:

a band division means for dividing a signal wavelength band of an incoming wavelength multiplexed light into at least a first band and second band;

said first band has tendency of decreasing power of outgoing light of an optical amplifier per channel at a decrease in the number of signal wavelengths or increasing power of the outgoing light of said optical amplifier per channel at an increase in the number of signal wavelengths and said second band, is a signal wavelength band other than said first band, including a gain deviation band in which power of the outgoing light per channel varies mainly due to a wavelength deviation of automatic gain control in the optical amplifier; and

an adjustment means for adjusting the power of the outgoing light for the individual divided bands devided by the band division means.

38. The individual band gain equalizer according to claim 37, wherein said band division means divides said signal wavelength band into three bands:

an SHB band, said gain deviation band and an SRS band, said SHB band being under dominance of a spectral hole burning (SHB) effect as said first band, and said SRS band being under dominance of a stimulated Raman scattering (SRS) effect occurring in an output transmission line of said optical amplifier as another band of said first band.

39. The individual band gain equalizer according to claim 38, wherein said adjustment means includes:

a variable optical attenuator for said SHB band;

a variable optical attenuator for said gain deviation band; and

a variable optical attenuator for said SRS band, and

said band division means includes;

a gain deviation band reflection device for reflecting light in said gain deviation band;

a first optical circulator for leading said incoming wavelength multiplexed light to said gain deviation band reflection device and leading reflected light from said gain deviation band reflection device to said variable optical attenuator for said gain deviation band;

a band separation device for separating light passing through the gain deviation band reflection device into light in said SHB band and light in said SRS band to lead the lights to said variable optical attenuators for said SHB band and said SRS band;

a band coupling device for coupling output lights of said SHB band and SRS band variable optical attenuators; and

a second optical circulator provided on an output side of said gain deviation band variable optical attenuator for leading output light from said band coupling device to said gain deviation band variable optical attenuator side and for leading light inputted from said gain deviation band variable optical attenuator side to an output port;

an SHB band reflection device, provided between said gain deviation band variable optical attenuator and said second optical circulator, for reflecting, of light led to said gain deviation band variable optical attenuator side, light in said SHB band; and

an SRS band reflection device, provided between said gain deviation band variable optical attenuator and said second optical circulator, for reflecting, of light led to said gain deviation band variable optical attenuator side, light in said SRS band.

40. The individual band gain equalizer according to claim 39, wherein each of said variable optical attenuators is a high-speed variable optical attenuator having a response speed on the order of microsecond.

41. The individual band gain equalizer according to claim 38, wherein said band division means includes:

a first edge filter having a leading edge portion of a transmission band with respect to a wavelength in the vicinity of the boundary between said SHB band and said gain deviation band and having a transmission characteristic with respect to light with a wavelength on a longer-wavelength side from said leading edge portion; and

a second edge filter having a trailing edge portion of a transmission band with respect to a wavelength in the vicinity of the boundary between said gain deviation band and said SRS band and having a transmission characteristic with respect to light with a wavelength on a shorter-wavelength side from said trailing edge portion, and

said adjustment means includes;

a variable optical attenuator for adjusting output light power of said second edge filter; and

a transmission wavelength control unit for controlling a transmission light quantities of said SHB band and said SRS band independently by shifting said edge portions of said edge filters individually.

42. The individual band gain equalizer according to claim 38, wherein said band division means includes:

a first transmission fiber grating having an adjustment function to adjust a transmission light quantity of light in said SHB band contained in said inputted wavelength multiplexed light; and

second transmission fiber grating having an adjustment function to adjust a transmission light quantity of light in said SRS band contained in output light of said first transmission fiber grating, and

said adjustment means includes;

a variable optical attenuator for adjusting output light power of said second transmission fiber grating; and

a transmission quantity control unit for applying a temperature or pressure variation to each of said transmission fiber gratings individually to control a transmission light quantity of each of said transmission fiber gratings independently.

43. A wavelength multiplexing transmission apparatus using an individual band gain equalizer, comprising:

said individual band gain equalizer including;

a band division means for dividing a signal wavelength band of an incoming wavelength multiplexed light into at least a first band and second band;

said first band has tendency of decreasing power of out going light of an optical amplifier per channel at a decrease in the number of signal wavelengths or increasing power of the outgoing light per channel at an increase in the number of signal wavelengths and said second band, is a signal wavelength band other than this band, including a gain deviation band in which power of the outgoing light per channel varies mainly due to a wavelength deviation of automatic gain control in the optical amplifier; and

an adjustment means for adjusting the power of the outgoing light for the individual divided bands devided by said band division means, and

control means for monitoring power of input light or output light of said individual band gain equalizer for each of the divided bands to control the output light power adjustment for the individual divided bands in said adjustment means based on a result of the monitoring so that output light power of each of the divided bands becomes a predetermined target value.

44. The wavelength multiplexing transmission apparatus according to claim 43, wherein said control means includes:

an individual band monitoring unit for monitoring power of input light or output light of said individual band gain equalizer for each of the divided bands;

a storage unit for storing said target value in advance;

a difference detection unit for detecting a difference between a result of the monitoring by said individual band monitoring unit and said target value in said storage unit for each of the divided bands; and

a gain equalization control unit for controlling said adjustment means so that the difference detected by said difference detection unit for each of the divided bands reaches a minimum.

45. The wavelength multiplexing transmission apparatus according to claim 43, wherein said wavelength multiplexing transmission apparatus is arranged as a wavelength add/drop apparatus having an add/drop unit made to add/drop light with a wavelength forming at least a portion of said inputted wavelength multiplexed light, and

said individual band gain equalizer is provided at a former or latter stage of said add/drop unit.

46. A wavelength multiplexing transmission system using an individual band gain equalizer, comprising a wavelength multiplexing transmission apparatus including an individual band gain equalizer, wherein said individual band gain equalizer comprising:

a band division means for dividing a signal wavelength band of an incoming wavelength multiplexed light into at least a first band and second band;

said first band has tendency of decreasing power of out going light of an optical amplifier per channel at a decrease in the number of signal wavelengths or increasing power of the outgoing light per channel at an increase in the number of signal wavelengths and said second band, is a signal wavelength band other than this band, including a gain deviation band in which power of the outgoing light per channel varies mainly due to a wavelength deviation of automatic gain control in the optical amplifier; and

an adjustment means for adjusting the power of the outgoing light for the individual divided bands devided by said band division means, and

control means for monitoring power of input light or output light of said individual band gain equalizer for each of the divided bands to control the output light power adjustment for the individual divided bands in said adjustment means based on a result of the monitoring so that output light power of each of the divided bands becomes a predetermined target value.

47. An optical amplifier using an individual band gain equalizer, comprising:

an amplification medium for amplifying incoming wavelength multiplexed light;

an automatic gain control unit for carrying out automatic gain control based on power of incoming light and outgoing light of said amplification medium and a target gain;

a individual band gain equalizer for dividing a signal wavelength band of an outgoing light of said amplification medium into at least a first band and second band;

said first band has tendency of decreasing power of the outgoing light per channel at a decrease in the number of signal wavelengths or increasing power of the outgoing light per channel at an increase in the number of signal wavelengths and said second band, is a signal wavelength band other than said first band, including a gain deviation band in which power of the outgoing light varies mainly due to a wavelength deviation of the automatic gain control so as to adjust the power of the outgoing light for the individual divided bands; and

control means for monitoring the power of the outgoing light of said amplification medium for each of the divided bands to control said output light power adjustment of said band unit gain equalizer for each of the divided bands based on a result of the monitoring so that the power of the outgoing light of each of the divided bands becomes a predetermined target value.

48. The optical amplifier according to claim 47, wherein said control means includes:

an individual band monitoring unit for monitoring output light power of said amplification medium for each of the divided bands;

a storage unit for storing said target value in advance;

a difference detection unit for detecting a difference between a result of the monitoring by said individual band monitoring unit and said target value in said storage unit for each of the divided bands; and

a gain equalization control unit for controlling said individual band gain equalizer so that the difference detected by said difference detection unit for each of the divided bands reaches a minimum.

49. A wavelength multiplexing transmission system using an individual band gain equalizer, comprising:

said individual band gain equalizer including;

a band division means for dividing a signal wavelength band of an incoming wavelength multiplexed light into at least a first band and second band;

said first band has tendency of decreasing of power of the outgoing light of an optical amplifier per channel at a decrease in the number of signal wavelengths or increasing of power of the outgoing light per channel at an increase in the number of signal wavelengths and said second band, is a signal wavelength band other than said first band, including a gain deviation band in which power of the outgoing light per channel varies mainly due to a wavelength deviation of automatic gain control in the optical amplifier; and

an adjustment means for adjusting the output light power for the individual divided bands devided by said band division means, and

an optical amplifier including;

control means for monitoring power of input light or output light of said individual band gain equalizer for each of the divided bands to control the output light power adjustment for the individual divided bands in said adjustment means based on a result of the monitoring so that power of the output light of each of the divided bands becomes a predetermined target value.