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An apparatus and method are described for exploiting almost the full almost 25 TH % of bandwidth available in the low-loss window in optical fibers (from 1430 nm-1620 nm) using a parallel combination of optical amplifiers. The low-loss window at about 1530 nm-1620 nm can be amplified using erbium-d

An apparatus and method are described for exploiting almost the full almost 25 TH % of bandwidth available in the low-loss window in optical fibers (from 1430 nm-1620 nm) using a parallel combination of optical amplifiers. The low-loss window at about 1530 nm-1620 nm can be amplified using erbium-doped fiber amplifiers (EDFAs). However, due to the inherent absorption of the erbium at shorter wavelengths, EDFAs cannot be used below about 1525 nm without a significant degradation in performance. For the low-loss window at approximately 1430-1530 nm, amplifiers based on nonlinear polarization in optical fibers can be used effectively. A broadband nonlinear polarization amplifier (NLPA) is disclosed which combines cascaded Raman amplification with parametric amplification or four-wave mixing. In particular, one of the intermediate cascade Raman order wavelengths λ r should lie in close proximity to the zero-dispersion wavelength λ 0 of the amplifying fiber. For this intermediate Raman order, spectral broadening will occur due to phase-match 15 with four-wave mixing (if λ r <λ 0 ) or phase-matched parametric amplification (if λ r <λ 0 ). In further cascaded Raman orders, the gain spectrum will continue to broaden due to the convolution of the gain spectrum with the spectrum from the previous Raman order.

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1. A nonlinear polarization amplifier stage comprising:a gain medium operable to receive a multiple wavelength optical signal comprising wavelengths within a range λ s ;a pump operable to generate at least one pump wavelength λ p for introduction to the gain medium; anda coupler operab

1. A nonlinear polarization amplifier stage comprising:a gain medium operable to receive a multiple wavelength optical signal comprising wavelengths within a range λ s ;a pump operable to generate at least one pump wavelength λ p for introduction to the gain medium; anda coupler operable to introduce the at least one pump wavelength to the gain medium to facilitate Raman amplification of at least a portion of the multiple wavelength optical signal;wherein at least an intensity of the at least one pump wavelength is selected to affect the shape of a gain curve associated with the multiple wavelength optical signal in the amplifier stage; andwherein at least a portion of the gain medium comprising a zero-dispersion wavelength λ 0 , which is less than or equal to at least one signal wavelength λ s and greater than or equal to λ p . 2. The nonlinear polarization amplifier stage of claim 1, wherein the gain medium comprises a distributed gain medium. 3. The nonlinear polarization amplifier stage of claim 1, wherein the gain medium comprises an optical fiber. 4. The nonlinear polarization amplifier stage of claim 1, wherein the zero-dispersion wavelength comprises approximately 1310 nanometers. 5. The nonlinear polarization amplifier stage of claim 1, wherein the zero-dispersion wavelength comprises approximately 1550 nanometers. 6. The nonlinear polarization amplifier stage of claim 1, wherein the zero-dispersion wavelength is within a range of 1390 nanometers and 1540 nanometers. 7. The nonlinear polarization amplifier stage of claim 1, wherein the wavelength range λ s resides within a wavelength range of 1430 to 1530 nanometers. 8. The nonlinear polarization amplifier stage of claim 1, wherein at least a portion of the gain medium comprises a zero-dispersion wavelength λ 0 , which is within thirty (30) nanometers of λ p . 9. The nonlinear polarization amplifier stage of claim 1, wherein the pump comprises part of a pump assembly operable to generate a plurality of pump wavelengths within a wavelength range λ p1 -λ pn . 10. The nonlinear polarization amplifier stage of claim 9, wherein the pump assembly comprises a grating based Raman oscillator pumped by a cladding-pumped fiber laser. 11. The nonlinear polarization amplifier stage of claim 9, wherein at least a portion of the gain medium comprises a zero-dispersion wavelength λ 0 , which is less than or equal to at least one wavelength λ s and greater than or equal to at least one pump wavelength λ p of the plurality of pump wavelengths. 12. The nonlinear polarization amplifier stage of claim 9, wherein at least a portion of the gain medium comprises a zero-dispersion wavelength λ 0 , which is within thirty (30) nanometers of at least one pump wavelength λ p of the plurality of pump wavelengths. 13. The nonlinear polarization amplifier stage of claim 9, wherein the wavelengths or the intensities of at least some of the plurality of pump wavelengths are selected to affect the shape of the gain curve associated with the multiple wavelength optical signal in the amplifier stage. 14. The nonlinear polarization amplifier stage of claim 9, further comprising a controller operable to control wavelengths of the pump signals output from the pump assembly to affect the shape of the amplifier gain curve. 15. The nonlinear polarization amplifier stage of claim 9, wherein at least some of the plurality of pump wavelengths differ by at least twenty (20) nanometers. 16. The nonlinear polarization amplifier stage of claim 9, wherein at least some of the plurality of pump wavelengths differ by seventy (70) nanometers or less. 17. A method of controlling the shape of a gain curve of a nonlinear polarization amplifier stage, comprising:receiving a multiple wavelength signal at a gain medium of a Raman amplifier stage, wherein the wavelengths of the multiple wavelength signal are within a wavele ngth range λ s ;selecting at least an intensity of a pump signal, wherein the resulting pump signal comprises a wavelength λ p ; andintroducing the pump signal to the gain medium to facilitate amplification of at least a portion of the multiple wavelength signal over at least a portion of the gain medium;wherein the shape of a gain curve for the amplifier stage is determined at least in part based on the selection of the wavelength or intensity of the pump signal; andwherein at least a portion of the gain medium comprises a zero-dispersion wavelength λ 0 , which is less than or equal to at least one wavelength λ s and greater than or equal to λ p . 18. The method of claim 17, wherein the gain medium comprises a distributed gain medium. 19. The method of claim 18, wherein the distributed gain medium provides distributed Raman amplification. 20. The method of claim 17, wherein the zero-dispersion wavelength comprises approximately 1310 nanometers. 21. The method of claim 17, wherein the zero-dispersion wavelength comprises approximately 1550 nanometers. 22. The method of claim 17, wherein the zero-dispersion wavelength is within a range of 1390 nanometers and 1540 nanometers. 23. The method of claim 17, wherein the wavelength range λ s comprises 1430 to 1530 nanometers. 24. The method of claim 17, wherein at least a portion of the gain medium comprises a zero-dispersion wavelength λ 0 , which is within thirty (30) nanometers of λ p . 25. The method of claim 17, wherein the pump signal comprises a multiple wavelength pump signal comprising a plurality of pump wavelengths within a wavelength range λ p1 -λ pn . 26. The method of claim 25, wherein selecting at least an intensity of the pump signal comprises selecting at least an intensity of at least some of a plurality of pump wavelengths. 27. The method of claim 25, wherein the intensities of at least some of the plurality of pump wavelengths are selected to affect the shape of the gain curve associated with the multiple wavelength optical signal in the amplifier stage. 28. The method of claim 25, further comprising changing the wavelength of a pump signal communicated to the gain medium to affect the shape of the gain curve associated with the multiple wavelength optical signal in the amplifier stage. 29. The method of claim 25, wherein at least some of the plurality of pump wavelengths differ by at least twenty (20) nanometers. 30. The method of claim 25, wherein at least some of the plurality of pump wavelengths differ by seventy (70) nanometers or less. 31. The method of claim 17, wherein at least a portion of the gain medium comprises a zero-dispersion wavelength λ 0 , which is within thirty (30) nanometers of at least one pump wavelength λ p of the plurality of pump wavelengths. 32. A nonlinear polarization amplifier stage comprising:a gain medium operable to receive a multiple wavelength optical signal comprising wavelengths within a range λ s , at least a portion of the gain medium comprising a zero-dispersion wavelength λ 0 ;a pump operable to generate at least one pump wavelength λ p for introduction to the gain medium, wherein the at least one pump wavelength λ p is within thirty (30) nanometers of the zero-dispersion wavelength λ 0 ; anda coupler operable to introduce the at least one pump wavelength to the gain medium to facilitate Raman amplification of at least a portion of the multiple wavelength optical signal;wherein at least an intensity of the at least one pump wavelength is selected to affect the shape of a gain curve associated with the multiple wavelength optical signal in the amplifier stage. 33. A method of controlling the shape of a gain curve of a nonlinear polarization amplifier stage, comprising:receiving a multiple wavelength signal at a gain medium of a Raman amplifier stage, at least a portion of the gain medium comprising a zero-di spersion wavelength λ 0 , wherein the wavelengths of the multiple wavelength signal are within a wavelength range λ s ;selecting at least an intensity of a pump signal, wherein the resulting pump signal comprises a wavelength λ p and wherein the wavelength λ p is within thirty (30) nanometers of the zero-dispersion wavelength λ 0 ; andintroducing the pump signal to the gain medium to facilitate amplification of at least a portion of the multiple wavelength signal over at least a portion of the gain medium;wherein the shape of a gain curve for the amplifier stage is determined at least in part based on the selection of the wavelength or intensity of the pump signal.