Apparatus and method for optical equalization and amplification

• US 5,812,710 A
• Filed: 12/20/1996
• Issued: 09/22/1998
• Est. Priority Date: 02/07/1996
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Sugaya, Yasushi
• Primary Examiner(s): Lee, John D.
• Application Number:
  US08/771,756
• Time in Patent Office: 641 Days
• Field of Search: 385/15, 385/24, 385/27, 385/31, 385/39, 359/124, 359/127-131, 359/154, 359/161, 359/173, 359/174, 359/179, 359/333, 359/337-339, 359/341, 359/349
• US Class Current: 385/27
• CPC Class Codes: H01S 2301/04 Gain spectral shaping, flattening
• CPC Class Codes: H01S 2301/06 Gain non-linearity, distortion; Compensation thereof
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/06787 Bidirectional amplifier
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/1301 in optical amplifiers
• CPC Class Codes: H01S 3/13013 by controlling the optical pumping
• CPC Class Codes: H04B 10/077 using a supervisory or additional signal
• CPC Class Codes: H04B 10/07955 Monitoring or measuring power
• CPC Class Codes: H04B 10/2941 using an equalising unit, e.g. a filter H04B10/296 takes precedence
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant

Abstract

A variable optical attenuator is provided at an input terminal of a rare-earth doped optical fiber. The variable optical attenuator attenuates a multiwavelength light under the control of an AGBC circuit. The rare-earth doped optical fiber, which is excited by an excitation light generated by a light source, amplifies the multiwavelength light output from the variable optical attenuator. An ALC circuit controls the light source in such a way that an average optical level of the multiwavelength light output from the rare-earth doped optical fiber is kept constant. The wavelength division multiplexing coupler selects two optical signals having different wavelengths from the multiwavelength light amplified by the rare-earth doped optical fiber. The AGBC circuit controls the attenuation of the variable optical attenuator in such a way that the above described two optical signal levels match each other.

Claims

1. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

a variable optical attenuator for adjusting an optical level of the multiwavelength light;

a first optical fiber amplifying unit for receiving and amplifying a multiwavelength light output from said variable optical attenuator in accordance with an excitation light provided to said first optical fiber amplifying unit;

a light source for providing the excitation light to said first optical fiber amplifying unit; and

control means for controlling a light intensity of said light source in such a way that the optical level of the multiwavelength light output from said first optical fiber amplifying unit is kept constant, and for controlling attenuation of said variable optical attenuator in such a way that each of optical levels of a plurality of wavelength bands in the multiwavelength light output from said first optical fiber amplifying unit matches each other irrespective of wavelength dependency of the optical levels of the plurality of wavelength bands in the multiwavelength light when received by the first optical fiber amplifying unit.

2. The optical equalizing amplifier according to claim 1, further comprising before said variable optical attenuator:

a second optical fiber amplifying unit for amplifying the multiwavelength light with a constant gain.

3. The optical equalizing amplifier according to claim 1, further comprising before said variable optical attenuator:

a third optical fiber amplifying unit for receiving a constant excitation light and amplifying the multiwavelength light.

4. The optical equalizing amplifier according to claim 1, wherein

said control means makes a portion of the multiwavelength light output from said first optical fiber amplifying unit branch into a plurality of wavelength bands, and controls attenuation of said variable optical attenuator such that a detected optical level of a shortest wavelength band equals a detected optical level of a longest wavelength band of wavelength bands whose optical levels exceed a predetermined level.

5. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

a first optical fiber amplifying unit for receiving and amplifying the multiwavelength light in accordance with an excitation light provided to said first optical fiber amplifying unit;

a light source for providing the excitation light to said first optical fiber amplifying unit;

a variable optical attenuator for adjusting an optical level of a multiwavelength light output from said first optical fiber amplifying unit; and

control means for controlling a light intensity of said light source in such a way that optical levels of a plurality of wavelength bands in the multiwavelength light output from said first optical fiber amplifying unit match each other irrespective of wavelength dependency of the optical levels of the plurality of wavelength bands in the multiwavelength light when received by the first optical fiber amplifying unit, and for controlling attenuation of said variable optical attenuator in such a way that the optical level of the multiwavelength light output from said variable optical attenuator is kept constant.

6. The optical equalizing amplifier according to claim 5, further comprising:

a second optical fiber amplifying unit for amplifying with a constant gain the multiwavelength light output from said variable optical attenuator.

7. The optical equalizing amplifier according to claim 5, further comprising:

a third optical fiber amplifying unit for receiving a constant excitation light and amplifying the multiwavelength light output from said variable optical attenuator.

8. The optical equalizing amplifier according to claim 5, further comprising:

a fourth optical fiber amplifying unit after said variable optical attenuator, wherein

an optical level of the multiwavelength light output from said fourth optical fiber amplifying unit is controlled to be kept constant.

9. The optical equalizing amplifier according to claim 5, wherein

said control means makes a portion of the multiwavelength light output from said first optical fiber amplifying unit branch into a plurality of wavelength bands, and controls the light intensity of said light source such that a detected optical level of a shortest wavelength band equals a detected optical level of a longest wavelength band of wavelength bands whose optical levels exceed a predetermined level.

10. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

an optical fiber amplifying unit for receiving and amplifying the multiwavelength light with a plurality of optical fiber amplifiers connected in series, said optical fiber amplifiers having different amplification characteristics dependant on wavelength;

a plurality of light sources for providing excitation lights to the plurality of optical fiber amplifiers; and

control means for controlling each light intensity of said plurality of light sources in such a way that each of optical levels of a plurality of wavelength bands in the multiwavelength light output from said optical fiber amplifying unit matches each other irrespective of wavelength dependency of the optical levels of the plurality of wavelength bands in the multiwavelength light when received by the optical fiber amplifying unit.

11. An optical equalizer for equalizing a multiwavelength light, comprising:

an optical fiber amplifying unit for amplifying a multiwavelength light;

a variable optical attenuator for adjusting an optical level of the multiwavelength light input to said optical fiber amplifying unit; and

control means for selecting a plurality of wavelength bands from a portion of the multiwavelength light output from said optical fiber amplifying unit and for controlling attenuation of said variable optical attenuator in such a way that each optical level of each wavelength band matches each other.

12. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

optical level adjusting means for adjusting an optical level of a multiwavelength light;

an optical fiber amplifying unit for amplifying the multiwavelength light output from said optical level adjusting means in accordance with an excitation light provided to said optical fiber amplifying unit;

a light source for providing the excitation light to said optical fiber amplifying unit; and

control means for controlling a light intensity of the light source in such a way that the optical level of the multiwavelength light output from said optical fiber amplifying unit is kept constant, and for controlling said optical level adjusting means so as to equalize optical levels of a plurality of wavelength bands in the multiwavelength light output from said optical fiber amplifying unit.

13. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

an optical fiber amplifying unit for amplifying the multiwavelength light in accordance with an excitation light provided to said optical fiber amplifying unit;

a light source for providing the excitation light to said optical fiber amplifying unit;

optical level adjusting means for adjusting an optical level of a multiwavelength light output from said optical fiber amplifying unit; and

control means for controlling a light intensity of the light source so as to equalize optical levels of a plurality of wavelength bands in the multiwavelength light output from said optical fiber amplifying unit, and for controlling said optical level adjusting means in such a way that the optical level of the multiwavelength light output from said optical level adjusting means is kept constant.

14. An optical equalizer for equalizing a multiwavelength light, comprising:

an optical fiber amplifying unit for receiving and amplifying a multiwavelength light;

optical level adjusting means for adjusting an optical level of the multiwavelength light input to said optical fiber amplifying unit; and

control means for controlling said optical level adjusting means in such a way that each optical level of each of a plurality of wavelength bands in the multiwavelength light output from said optical fiber amplifying unit matches each other irrespective of wavelength dependency of the optical levels when the multiwavelength light is received by the optical fiber amplifying unit.

15. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

optical level adjusting means for adjusting an optical level of a wavelength division multiplexed optical light;

optical fiber amplifying unit for amplifying the multiwavelength light output from said optical level adjusting means;

a light source for providing an excitation light to said optical fiber amplifying unit; and

branch means comprising a plurality of wavelength transmission bands for generating a plurality of lights having different wavelength components from a portion of the multiwavelength light amplified by said optical fiber amplifying unit; and

control means for controlling a light intensity of the light source in such a way that the optical level of the multiwavelength light output from said optical fiber amplifying unit is kept constant, and for controlling said optical level adjusting means based on a plurality of optical levels output from said branch means.

16. An optical amplifying/equalizing method for equalizing a multiwavelength light, comprising the steps of:

adjusting an optical level of the multiwavelength light using a variable optical attenuator;

amplifying the multiwavelength light whose optical level has been adjusted by the variable optical attenuator, the amplifying being performed by an optical fiber amplifier in accordance with an excitation light provided to the optical fiber amplifier;

controlling the optical level of the excitation light provided to the optical fiber amplifier in such a way that the optical level of the multiwavelength light output from the optical fiber amplifier is kept constant, and

controlling attenuation of the variable optical attenuator so as to equalize optical levels of a plurality of wavelength bands in the multiwavelength light.

17. An optical equalizing/amplifying method for equalizing a multiwavelength light, comprising the steps of:

amplifying the multiwavelength light using an optical fiber amplifier in accordance with an excitation light provided to the optical fiber amplifier;

adjusting, using a variable optical attenuator, an optical level of the multiwavelength light amplified by the optical fiber amplifier;

controlling the optical level of the excitation light provided to the optical fiber amplifier so as to equalize the output level of a plurality of wavelength bands in the multiwavelength light; and

controlling attenuation of the variable optical attenuator in such a way that the optical level of the multiwavelength light output from the variable optical attenuator is kept constant.

18. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

a variable optical attenuator for adjusting an optical level of the multiwavelength light;

a first optical fiber amplifying unit for amplifying a multiwavelength light output from the variable optical attenuator in accordance with an excitation light provided to the first optical fiber amplifying unit;

a light source for providing the excitation light to the first optical fiber amplifying unit; and

control means for controlling a light intensity of the light source in such a way that the optical level of the multiwavelength light output from the first optical fiber amplifying unit is kept constant, and for controlling attenuation of the variable optical attenuator in such a way that each of optical levels of a plurality of wavelength bands in the multiwavelength light output from the first optical fiber amplifying unit matches each other,

wherein the control means makes a portion of the multiwavelength light output from the first optical fiber amplifying unit branch into a plurality of wavelength bands, and controls attenuation of the variable optical attenuator such that a detected optical level of a shortest wavelength band equals a detected optical level of a longest wavelength band of wavelength bands whose optical levels exceed a predetermined level.

19. An optical equalizing amplifier for equalizing a multiwavelength light, comprising:

a first optical fiber amplifying unit for amplifying the multiwavelength light in accordance with an excitation light provided to the first optical fiber amplifying unit;

a light source for providing the excitation light to the first optical fiber amplifying unit;

a variable optical attenuator for adjusting an optical level of a multiwavelength light output from the first optical fiber amplifying unit; and

control means for controlling a light intensity of the light source in such a way that optical levels of a plurality of wavelength bands in the multiwavelength light output from the first optical fiber amplifying unit match each other, and for controlling attenuation of the variable optical attenuator in such a way that the optical level of the multiwavelength light output from the variable optical attenuator is kept constant,

wherein the control means makes a portion of the multiwavelength light output from the first optical fiber amplifying unit branch into a plurality of wavelength bands, and controls the light intensity of the light source such that a detected optical level of a shortest wavelength band equals a detected optical level of a longest wavelength band of wavelength bands whose optical levels exceed a predetermined level.

20. An apparatus for amplifying a multiwavelength light including first and second wavelength bands at first and second optical levels, respectively, the apparatus comprising:

a variable optical attenuator adjusting the first and second optical levels in the multiwavelength light;

an optical amplifier amplifying the first and second optical level adjusted multiwavelength light; and

a controller controlling the optical amplifier to maintain the amplified multiwavelength light at a constant power level, and controlling the variable optical attenuator to equalize the first and second optical levels in the amplified multiwavelength light.

21. An apparatus as in claim 20, wherein

the optical amplifier receives an excitation light and amplifies the multiwavelength light in accordance with the power level of the excitation light, and

the controller controls the optical amplifier by controlling the power level of the excitation light.

22. An apparatus as in claim 20, wherein

the multiwavelength light includes more than two wavelength bands, each at a corresponding optical level,

the variable optical attenuator adjusts the optical level of each wavelength band in the multiwavelength light,

the optical amplifier amplifies the optical level adjusted multiwavelength light;

and

the controller controls the optical amplifier to maintain the amplified multiwavelength light at a constant power level, and controls the variable optical attenuator to equalize the optical levels of the wavelength bands in the amplified multiwavelength light.

23. An apparatus for amplifying a multiwavelength light including first and second wavelength bands at first and second optical levels, respectively, the apparatus comprising:

an optical amplifier amplifying the multiwavelength light;

a variable optical attenuator adjusting the first and second optical levels in the amplified multiwavelength light; and

a controller controlling the optical amplifier to equalize the first and second optical levels, and controlling the variable optical attenuator to maintain the amplified multiwavelength light at a constant power level.

24. An apparatus as in claim 23, wherein

the optical amplifier receives an excitation light and amplifies the multiwavelength light in accordance with the power level of the excitation light, and

the controller controls the optical amplifier by controlling the power level of the excitation light.

25. An apparatus as in claim 23, wherein

the multiwavelength light includes more than two wavelength bands, each at a corresponding optical level,

the optical amplifier amplifies the multiwavelength light;

the variable optical attenuator adjusts the optical level of each wavelength band in the amplified multiwavelength light, and

the controller controls the optical amplifier to equalize the optical levels of the wavelength bands in the amplified multiwavelength light, and controls the variable optical attenuator to maintain the amplified multiwavelength light at a constant power level.

26. A method for amplifying a multiwavelength light including first and second wavelength bands at first and second optical levels, respectively, the method comprising the steps of:

adjusting the first and second optical levels in the multiwavelength light; and

amplifying the first and second optical level adjusted multiwavelength light, wherein

the amplifying step maintains the amplified multiwavelength light at a constant power level, and

the adjusting step equalizes the first and second optical levels in the amplified multiwavelength light.

27. A method for amplifying a multiwavelength light including first and second wavelength bands at first and second optical levels, respectively, the method comprising the steps of:

amplifying the multiwavelength light; and

adjusting the first and second optical levels in the amplified multiwavelength light, wherein

the amplifying step equalizes the first and second optical levels, and

the adjusting step maintains the amplified multiwavelength light at a constant power level.