Low-noise distributed Raman amplifier using bi-directional pumping using multiple Raman orders

• US 6,631,025 B2
• Filed: 01/12/2001
• Issued: 10/07/2003
• Est. Priority Date: 01/12/2000
• Status: Expired due to Term

• Current Assignee: Neptune Subsea IP Ltd. (Xtera Topco Ltd.)
• Original Assignee: Xtera Communications Incorporated (Xtera Topco Ltd.)
• Inventors: Islam, Mohammed N., Freeman, Michael
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US09/760,201
• Publication Number:
  US 20030016437A1
• Time in Patent Office: 998 Days
• Field of Search: 359/334, 359/341.3, 359/341.31, 359/341.32, 359/341.33, 372/3, 372/6, 372/20
• US Class Current: 359/334
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/094011 with bidirectional pumping, i.e. with injection of the pump light from both two ends of the fibre
• CPC Class Codes: H01S 3/094015 with pump light recycling, i.e. with reinjection of the unused pump light back into the fiber, e.g. by reflectors or circulators
• CPC Class Codes: H01S 3/094096 Multi-wavelength pumping
• CPC Class Codes: H01S 3/302 in an optical fibre
• CPC Class Codes: H04B 10/2916 using Raman or Brillouin amplifiers
• CPC Class Codes: H04B 2210/258 treating each wavelength or wavelength band separately

Abstract

A Raman amplifier assembly includes a Raman amplifier configured to receive a signal from a signal source. The signal travels in an upstream direction in the Raman amplifier. A first pump source is coupled to the Raman amplifier. The first pump source produces a first pump beam that travels in a downstream direction and is counter-propagating relative to the signal. A second pump source is coupled to the Raman amplifier and produces a second pump beam that travels in the upstream direction. The second pump source has an average relative intensity noise of less than −80 dB/Hz.

Claims

1. A multi-stage Raman amplifier apparatus, comprising:

a first Raman amplifier configured to receive a signal of at least one wavelength traveling in an upstream direction in the first Raman amplifier;

a first pump source coupled to the first Raman amplifier producing a first pump beam in a downstream direction that is counter-propagating relative to the signal;

a second pump source coupled to the first Raman amplifier producing a second pump beam that travels in the upstream direction;

a second Raman amplifier coupled to the first Raman amplifier, wherein one of the first Raman amplifier and the second Raman amplifier comprises a distributed Raman amplifier and the other of the first Raman amplifier and the second Raman amplifier comprises a discrete Raman amplifier; and

a third pump source coupled to the second Raman amplifier producing a third pump beam traveling in the downstream direction.

2. The apparatus of claim 1, wherein the second pump beam pumps the first pump beam.

3. The apparatus of claim 1, wherein the second pump source has an average relative intensity noise of less than −

80 dB/Hz.

4. The apparatus of claim 3, wherein the average relative intensity noise from 1-10 GHz is less than −

80 dB/Hz.

5. The apparatus of claim 3, wherein the average relative intensity noise from 100 MHz to 1 GHz is less than −

90 dB/Hz.

6. The apparatus of claim 3, wherein the average relative intensity noise from 0-100 MHz is less than −

100 dB/Hz.

7. The apparatus of claim 1, further comprising:

a fourth pump source coupled to the second Raman amplifier producing a fourth pump beam that travels in the upstream direction.

8. The apparatus of claim 1, further comprising:

an isolator coupled to the second Raman amplifier.

9. The apparatus of claim 1, wherein the first Raman amplifier is a low-noise preamplifier and the second Raman amplifier is a power amplifier.

10. The apparatus of claim 1, further comprising:

a pump shunt coupled to the first and second Raman amplifiers.

11. The apparatus of claim 1, further comprising:

a first isolator positioned between the first and second Raman amplifiers.

12. The apparatus of claim 1, further comprising:

a pump shunt coupled to the first and second Raman amplifiers; and

a second isolator coupled to the pump shunt.

27. The apparatus of claim 1, wherein the first Raman amplifier comprises a Raman gain fiber with a non-linear gain coefficient (γ

) of greater than 3 W<sup>−

1</sup> km<sup>−

1</sup>.

28. The apparatus of claim 1, wherein the second Raman amplifier comprises a Raman gain fiber with a non-linear gain coefficient (γ

) of greater than 3 W<sup>−

1</sup> km<sup>−

1</sup>.

13. A method of amplifying on optical signal, comprising:

receiving at a first Raman amplifier a signal having at least one wavelength traveling in an upstream direction in the first Raman amplifier;

introducing to the first Raman amplifier a first pump beam traveling in a downstream direction that is counter-propagating relative to the signal;

introducing to the first Raman amplifier a second pump beam traveling in an upstream direction;

receiving at a second Raman amplifier coupled to the first Raman amplifier the signal traveling in an upstream direction;

introducing to the second Raman amplifier a third pump beam traveling in a downstream direction; and

wherein one of the first Raman amplifier and the second Raman amplifier comprises a distributed Raman amplifier and the other of the first Raman amplifier and the second Raman amplifier comprises a discrete Raman amplifier.

14. The method of claim 13, wherein the second pump beam pumps the first pump beam.

15. The method of claim 13, wherein the second pump beam is introduced to the first Raman amplifier by a pump source comprising an average relative intensity noise of less than −

80 dB/Hz.

16. The method of claim 15, wherein the average relative intensity noise from 1-10 GHz is less than −

80 dB/Hz.

17. The method of claim 15, wherein the average relative intensity noise from 100 MHz to 1 GHz is less than −

90 dB/Hz.

18. The method of claim 15, wherein the average relative intensity noise from 0-100 MHz is less than −

100 dB/Hz.

19. The method of claim 13, wherein the first Raman amplifier is a low-noise preamplifier and the second Raman amplifier is a power amplifier.

20. The method of claim 13, wherein the first Raman amplifier receives the signal from the second Raman amplifier.

21. The method of claim 13, wherein the second Raman amplifier receives the signal from the first Raman amplifier.

22. The method of claim 13, further comprising:

introducing to the second Raman amplifier a fourth pump beam traveling in a upstream direction.

23. The method of claim 13, further comprising:

coupling an isolator to the second Raman amplifier.

24. The method of claim 13, further comprising:

coupling a pump shunt to the first and second Raman amplifiers.

25. The method of claim 24, further comprising:

coupling a second isolator to the pump shunt.

26. The method of claim 13, further comprising:

coupling a first isolator between the first and second Raman amplifiers.