Multi-wavelength light amplifier

• US 6,055,092 A
• Filed: 05/28/1996
• Issued: 04/25/2000
• Est. Priority Date: 03/09/1995
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Sugaya, Yasushi, Kinoshita, Susumu, Takeda, Miki, Chikama, Terumi
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US08/655,027
• Time in Patent Office: 1,428 Days
• Field of Search: 359/174, 359/341, 359/134, 359/160, 359/179
• US Class Current: 359/337
• CPC Class Codes: H01S 2301/04 Gain spectral shaping, flattening
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/10015 by monitoring or controlling, e.g. attenuating, the input signal
• CPC Class Codes: H01S 3/1301 in optical amplifiers
• CPC Class Codes: H01S 3/13013 by controlling the optical pumping
• CPC Class Codes: H04B 10/296 Transient power control, e.g. due to channel add/drop or rapid fluctuations in the input power
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04J 14/02216 by gain equalization

Abstract

A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Claims

1. An apparatus comprising:

a multi-stage optical amplifying unit, for amplifying an input light, which includes

a first-stage optical amplifier which has an optical fiber for amplifying the input light to produce a first-stage amplified light;

a second-stage optical amplifier which has an optical fiber for amplifying the first-stage amplified light, to produce a second-stage amplified light; and

an attenuator positioned between the first-stage optical amplifier and the second-stage optical amplifier, to attenuate the power level of the first-stage amplified light and thereby control a power level of the second-stage amplified light.

2. An apparatus as in claim 1, wherein the attenuator attenuates the power level of the first-stage amplified light on the basis of the power level of the second-stage amplified light.

3. An apparatus comprising:

a multi-stage optical amplifying unit, for amplifying an input light, which includes

a first-stage optical amplifier which has an optical fiber for amplifying the input light, to produce a first-stage amplified light;

a second-stage optical amplifier which has an optical fiber for amplifying the first-stage amplified light, to produce a second-stage amplified light; and

a level controller controlling the power level of the first-stage amplified light based on a power level of the second-stage amplified light.

4. An apparatus as in claim 3, wherein the level controller comprises an attenuator positioned between the first-stage optical amplifier and the second-stage optical amplifier.

5. An apparatus as in claim 4, wherein the attenuator attenuates the power level of the first-stage amplified light, to control a power level of the second-stage amplified light.

6. An apparatus as in claim 5, wherein the attenuator attenuates the power level of the first-stage amplified light on the basis of the power level of the second-stage amplified light.

7. An apparatus as in claim 3, wherein the first-stage and second-stage optical amplifiers have different gain versus wavelength characteristics so that the multi-stage optical amplifying unit has a gain with substantially no wavelength-dependence.

8. An apparatus as in claim 4, wherein the first-stage and second-stage optical amplifiers have different gain versus wavelength characteristics so that the multi-stage optical amplifying unit has a gain with substantially no wavelength-dependence.

14. An apparatus as in claim 3, wherein the level controller controls the power level of the first-stage amplified light to maintain the power level of the second-stage amplified light at a constant level.

19. An apparatus as in claim 3, wherein the level controller comprises a detector detecting the power level of the second-stage amplified light, the level controller controlling the power level of the first-stage amplified light based on the power level detected by the detector.

20. An apparatus as in claim 4, wherein the level controller comprises a detector detecting the power level of the second-stage amplified light, the level controller controlling the power level of the first-stage amplified light based on the power level detected by the detector.

21. An apparatus as in claim 4, wherein the attenuator is an optical attenuator having a variable attenuation.

9. An apparatus comprising:

a multi-stage optical amplifying unit, for amplifying an input light, which includes

a first-stage optical amplifier which has an optical fiber for amplifying the input light, to produce a first-stage amplified light;

a second-stage optical amplifier which has an optical fiber for amplifying the first-stage amplified light, to produce a second-stage amplified light; and

a level controller including an attenuator positioned between the first-stage optical amplifier and the second-stage optical amplifier, to control a power level of the first-stage amplified light depending on a power level of the second-stage amplified light.

10. An apparatus as in claim 9, wherein the attenuator attenuates the power level of the first-stage amplified light on the basis of the power level of the second-stage amplified light.

11. An apparatus as in claim 9, wherein the first-stage and second-stage optical amplifiers have different gain versus wavelength characteristics so that the multi-stage optical amplifying unit has a gain with substantially no wavelength-dependence.

15. An apparatus as in claim 9, wherein the level controller controls the power level of the first-stage amplified light to maintain the power level of the second-stage amplified light at a constant level.

22. An apparatus as in claim 9, wherein the level controller comprises a detector detecting the power level of the second-stage amplified light, the level controller controlling the power level of the first-stage amplified light based on the power level detected by the detector.

23. An apparatus as in claim 9, wherein the attenuator is an optical attenuator having a variable attenuation.

12. A method comprising the steps of:

(a) optically amplifying an input light to produce a first-stage amplified light;

(b) optically amplifying the first-stage amplified light to produce a second-stage amplified light;

(c) controlling the power level of the first-stage amplified light in accordance with a power level of the second-stage amplified light; and

(d) performing said steps (a), (b) and (c) by a multi-stage optical amplifying unit.

16. A method as in claim 12, wherein said controlling controls the power level of the first-stage amplified light to maintain a power level of the second-stage amplified light at a constant level.

24. A method as in claim 12, further comprising:

detecting the power level of the second-stage amplified light, wherein said controlling controls the power level of the first-stage amplified light in accordance with said detected power level.

13. An apparatus comprising:

a multi-stage optical amplifying unit, for amplifying an input light, which includes;

a first-stage optical amplifier which has an optical fiber for amplifying the input light, to produce a first-stage amplified light;

a second-stage optical amplifier which has an optical fiber for amplifying the first-stage amplified light, to produce a second-stage amplified light; and

a level controller detecting a power level of the second-stage amplified light, and controlling the power level of the first-stage amplified light in accordance with said detected power level.

25. An apparatus as in claim 13, wherein the level controller comprises a detector detecting the power level of the second-stage amplified light.

17. An apparatus comprising:

a multi-stage optical amplifying unit, for amplifying an input light, which includes;

a first-stage optical amplifier which has an optical fiber for amplifying the input light, to produce a first-stage amplified light;

a second-stage optical amplifier which has an optical fiber for amplifying the first-stage amplified light, to produce a second-stage amplified light at an output port of the second-stage optical amplifier; and

a level controller controlling a power level of the first-stage amplified light based on a power level of the second-stage amplified light at the output port of the second-stage optical amplifier.

18. An apparatus as in claim 17, wherein the level controller comprises an attenuator positioned between the first-stage optical amplifier and the second-stage optical amplifier, to control the power level of the first-stage amplified light.

26. An apparatus as in claim 17, wherein the level controller comprises a detector detecting the power level of the second-stage amplified light at the output port of the second-stage optical amplifier, the level controller controlling the power level of the first-stage amplified light based on the power level detected by the detector.

27. An apparatus comprising:

a multi-stage optical amplifying unit, for amplifying an input light, which includes

a first-stage optical amplifier amplifying the input light, to produce a first-stage amplified light;

a second-stage optical amplifier amplifying the first-stage amplified light, to produce a second-stage amplified light;

a detector detecting a power level of the second-stage amplified light; and

an optical attenuator having a variable attenuation and positioned between the first-stage optical amplifier and the second-stage optical amplifier to attenuate the first-stage amplified light, the attenuation of the optical attenuator being controlled based on the power level detected by the detector.

28. A method comprising the steps of:

(a) optically amplifying an input light to produce a first-stage amplified light;

(b) optical amplifying the first-stage amplified light to produce a second-stage amplified light;

(c) attenuating a power level of the first-stage amplified light in accordance with a power level of the second-stage amplified light; and

(d) performing said steps (a), (b) and (c) by a multi-stage optical amplifying unit.

29. A method comprising the steps of:

(a) providing a multi-stage optical amplifying unit;

(b) optically amplifying an input light by a stage of the multi-stage optical amplifying unit to produce a first-stage amplified light;

(c) optical amplifying the first-stage amplified light by a stage of the multi-stage optical amplifying unit, different from said stage in step (b), to produce a second-stage amplified light;

(d) attenuating the power level of the first-stage amplified light in accordance with a power level of the second-stage amplified light, by the multi-stage optical amplifying unit; and

(e) outputting the second-stage amplified light as an output light of the multi-stage optical amplifying unit.

30. A method comprising the steps of:

(a) transmitting an optical signal through an optical fiber;

(b) providing a multi-stage optical amplifying unit;

(c) optically amplifying the optical signal received through the optical fiber by a stage of the multi-stage optical amplifying unit, to produce a first-stage amplified optical signal;

(d) optically amplifying the first-stage amplified optical signal by a stage of the multi-stage optical amplifying unit different from said stage in step (c), to produce a second-stage amplified optical signal;

(e) controlling the power level of the first-stage amplified optical signal in accordance with a power level of the second-stage amplified optical signal by the multi-stage optical amplifying unit;

(f) outputting the second-stage amplified optical signal as an output optical signal of the multi-stage optical amplifying unit; and

(g) transmitting the output optical signal through an optical fiber.