Hybrid raman/erbium-doped fiber amplifier and transmission system with dispersion map

• US 20030179440A1
• Filed: 03/14/2003
• Published: 09/25/2003
• Est. Priority Date: 03/15/2002
• Status: Active Grant

• Current Assignee: Tyco Electronics Subsea Communications LLC (TE Connectivity Limited)
• Original Assignee: Tyco Telecommunications Us Incorporated (Johnson Controls International plc)
• Inventors: Nissov, Morten, Lin, Chinlon, Pilipetskii, Alexei N., Foursa, Dmitri, Pedersen, Bo, Mills, Michael A.
• Granted Patent: US 7,085,039 B2
• Time in Patent Office: Days
• US Class Current: 359/334
• CPC Class Codes: H01S 2301/04 Gain spectral shaping, flattening
• CPC Class Codes: H01S 3/06725 Fibre characterized by a specific dispersion, e.g. for pulse shaping in soliton lasers or for dispersion compensating [DCF]
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/1608 erbium
• CPC Class Codes: H01S 3/2375 Hybrid lasers H01S3/07 takes precedence
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

A hybrid Raman-EDFA provides gain equalization over the C-band and L-band. The hybrid Raman-EDFA includes a Raman section producing a Raman gain and an EDFA section producing an EDFA gain complimenting the Raman gain. The EDFA section preferably includes a highly inverted, single-stage EDFA to produce the complimenting EDFA gain shape. One embodiment of the EDFA section includes a high return loss termination located after the erbium fiber to receive unabsorbed pump power. Multiple hybrid Raman-EDFAs can be connected in an amplifier chain in a transmission system. The transmission system preferably provides a dispersion map including regular composite fiber spans followed by at least one compensating span of negative dispersion fibers. The Raman sections of the hybrid Raman-EDFAs are preferably coupled to negative dispersion fiber in the transmission system.

Claims

1. A system for amplifying an optical signal, said system comprising:

a transmission path for transmitting said optical signal;

at least one Raman pump coupled to said transmission path for single wavelength unpolarized backward Raman pumping to produce Raman gain in said optical signal; and

a single-stage erbium doped fiber amplifier (EDFA) coupled to said transmission medium at the output of said Raman pumping to produce an EDFA gain in said optical signal complimenting said Raman gain, said EDFA including a length of erbium doped fiber and an EDFA pump coupled to said erbium doped fiber, wherein said EDFA is highly inverted such that gain shapes of said Raman gain and said EDFA gain are complimentary and provide a substantially flat composite gain shape.

2. The system of claim 1 wherein said Raman gain is predominantly in the L-band, and wherein said EDFA gain is predominantly in the C-band.

3. The system of claim 1 wherein said at least one Raman pump includes two polarization multiplexed lasers.

4. The system of claim 3 wherein said lasers are grating stabilized.

5. The system of claim 1 further comprising a circulator coupling the output of said at least one Raman pump to said transmission path.

6. The system of claim 1 wherein said at least one Raman pump has a wavelength of about 1497 nm.

7. The system of claim 1 wherein said EDFA pump has a wavelength of about 980 nm.

8. The system of claim 7 wherein said EDFA includes an isolator following said erbium doped fiber.

9. The system of claim 8 wherein said EDFA includes a gain flattening filter following said isolator.

10. The system of claim 1 further comprising a high return loss termination coupled after said erbium fiber such that unabsorbed radiation from said EDFA pump is directed to said termination.

11. The system of claim 10 further comprising a wavelength division multiplexer (WDM) at the output of said erbium doped fiber for directing said unabsorbed radiation from said EDFA pump to said high return loss termination.

12. The system of claim 10 wherein said high return loss termination includes a tightly bended fiber.

13. The system of claim 10 wherein said high return loss termination includes a double looped fiber and a thermoplastic surrounding at least a portion of said double looped fiber.

14. The system of claim 1 wherein said transmission path includes a dispersion slope matched fiber path, and wherein said Raman pump is coupled to a negative dispersion section of said dispersion slope matched fiber path.

15. The system of claim 1 wherein said transmission path includes a fiber span combining positive dispersion fibers having a large effective area followed by negative dispersion fibers having a small effective area, and wherein said Raman pump is coupled to said negative dispersion fibers.

16. A transmission system having a dispersion map, said transmission system comprising:

a transmitter and a receiver;

a transmission path between said transmitter and said receiver, said transmission path comprising;

a first group of composite fiber spans including a combination of positive dispersion fibers and negative dispersion fibers and having a residual positive dispersion;

at least one compensating span following said first group of composite fiber spans, said compensating span including negative dispersion fibers; and

a second group of composite fiber spans following said compensating span, said composite fiber spans in said second group including a combination of positive dispersion fibers and negative dispersion fibers and having a residual positive dispersion; and

a plurality of hybrid Raman-EDFAs connected respectively between said fiber spans, each of said Raman-EDFAs including a Raman section and an EDFA section, wherein each said Raman section is coupled to negative dispersion fibers of a respective one of said fiber spans.

17. The transmission system of claim 16 wherein said EDFA section includes a single-stage EDFA.

18. The transmission system of claim 17 wherein said Raman section provides single wavelength unpolarized backward Raman pumping in front of each said single-stage EDFA.

19. The transmission system of claim 18 wherein said single-stage EDFA is highly inverted such that gain shapes produced by said Raman section and said EDFA section are complimentary and provide a substantially flat composite gain shape.

20. The transmissions system of claim 16 wherein each said EDFA section includes a high return loss termination for receiving unabsorbed pump radiation.

21. The transmission system of claim 16 wherein said composite fiber spans include said positive dispersion fibers and said negative dispersion fibers in a 2:

1 ratio.

22. A system for amplifying an optical signal, said system comprising:

a transmission path for transmitting said optical signal;

at least one Raman pump coupled to said transmission path for producing Raman gain in said optical signal; and

an erbium doped fiber amplifier (EDFA) coupled to said transmission medium after said Raman pump for producing an EDFA gain in said optical signal complimenting said Raman gain, said EDFA including a length of erbium doped fiber, an EDFA pump coupled to said erbium doped fiber, and a high return loss termination coupled after said erbium fiber such that unabsorbed radiation from said EDFA pump is directed to said termination.

23. The system of claim 22 wherein said high return loss termination includes a double looped fiber and a thermoplastic surrounding at least a portion of said double looped fiber.

24. An erbium doped fiber amplifier (EDFA) comprising:

a length of erbium doped fiber;

an EDFA pump for forward pumping said erbium doped fiber;

a wavelength division multiplexer (WDM) at the output of said erbium doped fiber for redirecting unabsorbed pump radiation; and

a high return loss termination coupled to said WDM such that said unabsorbed pump radiation is directed to said termination.

25. A system for amplifying an optical signal, said system comprising:

a transmission span including a combination of large effective area and small effective area dispersion matched fibers;

at least one Raman pump coupled to said fiber with said small effective area for generating a pump wavelength and backward pumping said pump wavelength into said fiber span to produce Raman gain in said optical signal; and

an erbium doped fiber amplifier (EDFA) coupled after said Raman pump for producing EDFA gain in said optical signal complimenting said Raman gain, said EDFA including a length of erbium doped fiber and an EDFA pump coupled to said erbium doped fiber.

26. A transmission system having a dispersion map, said transmission system comprising:

a transmitter and a receiver;

a transmission path between said transmitter and said receiver, said transmission path comprising;

a first group of composite fiber spans including a combination of positive dispersion fibers and negative dispersion fibers and having a residual positive dispersion;

at least one compensating span following said first group of composite fiber spans, said compensating span including negative dispersion fibers; and

a second group of composite fiber spans following said compensating span, said composite fiber spans in said second group including a combination of positive dispersion fibers and negative dispersion fibers and having a residual positive dispersion; and

a plurality of optical amplifiers connected respectively between said fiber spans, wherein each said optical amplifiers is coupled to negative dispersion fibers of a respective one of said fiber spans.