System and method for fractional Raman order pumping in optical communication systems

1. An optical communication system comprising:

a gain medium capable of receiving at least one optical signal comprising one or more optical signal wavelengths;

one or more pump sources capable of generating at least a first pump signal and a second pump signal for introduction to the gain medium, the first pump signal comprising at least one integer Raman order band of pump wavelengths and the second pump signal comprising at least one fractional Raman order band of pump wavelengths, the at least one integer Raman order band of pump wavelengths comprising a plurality of integer Raman order pump wavelengths, each of the plurality of integer Raman order of pump wavelengths comprising a Raman gain peak that is one stokes shift from at least one of the one or more optical signal wavelengths, the at least one fractional Raman order band of pump wavelengths comprising a plurality of fractional Raman order pump wavelengths, each of the plurality of fractional Raman order pump wavelengths comprising a Raman gain peak that is a non-integer multiple of one stokes shift from each of the one or more optical signal wavelengths, wherein the non-integer multiple of one stokes shift from each of the one or more optical signal wavelengths is greater than 1.1 stokes shifts and less than 1.9 stokes shifts from each of the one or more optical signal wavelengths; and

wherein the at least one pump signal interacts with the optical signal as the pump signal traverses at least a portion of the gain medium.

2. The system of claim 1 , wherein the one or more pump sources comprise:

a first pump source capable of generating at least the second pump signal that co-propagates within the gain medium with at least a portion of the optical signal, the second pump signal comprising the plurality of fractional Raman order pump wavelengths having a Raman gain peak that is a non-integer multiple of one stokes shift from each of the one or more optical signal wavelengths; and

a second pump source capable of generating at least a third pump signal that counter-propagates within the gain medium with at least a portion of the optical signal, the third pump signal comprising one or more fractional Raman order pump wavelengths having a Raman gain peak that is a non-integer multiple of one stokes shift from each of the one or more optical signal wavelengths.

3. The system of claim 1 , wherein at least one of the one or more fractional Raman order pump wavelengths operates to amplify at least one of the integer Raman order pump wavelengths as the pump signal traverses the gain medium.

4. The system of claim 1 , wherein the optical communication system further comprises:

a first end terminal coupled to a first end the gain medium and adapted to generate the at least one optical signal comprising one or more optical signal wavelengths; and

a second end terminal coupled to a second end of the gain medium and adapted to receive the at least one optical signal comprising one or more optical signal wavelengths after traversing the gain medium, wherein the gain medium is substantially free from optical components that require electrical power.

5. The system of claim 1 , wherein at least one of the one or more fractional Raman order pump wavelengths comprises a Raman gain peak that is greater than approximately 1.3 stokes shifts from at least one of the one or more optical signal wavelengths and less than approximately 1.8 stokes shifts from at least one of the one or more optical signal wavelengths.

6. The system of claim 1 , wherein at least a portion of the gain medium comprises a distributed Raman amplifier that amplifies the optical signal through Raman gain.

7. The system of claim 1 , wherein the optical communication system comprises an unrepeatered optical communication system.

8. An unrepeatered optical communication system comprising:

a first end terminal coupled to a first end a transmission fiber and adapted to generate at least one optical signal comprising one or more optical signal wavelengths;

a second end terminal coupled to a second end of the transmission fiber and adapted to receive the at least one optical signal comprising one or more optical signal wavelengths after traversing the transmission fiber, wherein the transmission fiber is substantially free from optical components that require electrical power;

one or more pump sources capable of generating at least a first pump signal and a second pump signal for introduction to the transmission fiber, the first pump signal comprising a plurality of integer Raman order pump wavelengths and the second pump signal comprising a plurality of fractional Raman order pump wavelengths, each of the plurality of integer Raman order pump wavelengths comprising a Raman gain peak that is one stokes shift from at least one of the one or more optical signal wavelengths, each of the plurality of fractional Raman order pump wavelengths comprising a Raman gain peak that is a non-integer multiple of one stokes shift from all of the plurality of optical signal wavelengths, wherein the non-integer multiple of one stokes shift from all of the plurality of optical signal wavelengths is greater than 1.1 stokes shifts and less than 1.9 stokes shifts from all of the plurality of optical signal wavelengths; and

wherein the pump signal interacts with the at least one optical signal as the pump signal traverses the transmission fiber.

9. The system of claim 8 , wherein at least one of the plurality of fractional Raman order pump wavelengths operates to amplify at least one of the plurality of integer Raman order pump wavelengths as the pump signal traverses the transmission fiber.

10. The system of claim 8 , wherein the second pump signal co-propagates with the optical signal over at least a portion of the transmission fiber.

11. The system of claim 8 , wherein the first pump signal counter-propagates with at least a portion of the optical signal over at least a portion of the transmission fiber.

12. The system of claim 8 , wherein the transmission fiber comprises a length of at least two hundred kilometers.

13. The system of claim 8 , wherein at least one of the plurality of fractional Raman order pump wavelengths comprises a Raman gain peak that is greater than approximately 1.3 stokes shifts from at least one of the plurality of optical signal wavelengths and less than approximately 1.8 stokes shifts from at least one of the plurality of optical signal wavelengths.

14. A method of communicating an optical signal in an unrepeatered optical communication system, the method comprising:

communicating at least one optical signal comprising a plurality of optical signal wavelengths over a gain medium;

generating at least a first pump signal comprising a plurality of integer Raman order pump wavelengths and second pump signal comprising a plurality of fractional Raman order pump wavelengths, each of the plurality of integer Raman order pump wavelengths comprising a Raman gain peak that is one stokes shift from at least one of the one or more optical signal wavelengths, each of the plurality of fractional Raman order pump wavelengths comprising a Raman gain peak that is non-integer multiple of one stokes shift from each of the plurality of optical signal wavelengths, wherein the non-integer multiple of one stokes shift from each of the plurality of optical signal wavelengths is greater than 1.1 stokes shifts and less than 1.9 stokes shifts from each of the plurality of optical signal wavelengths; and

introducing the at least one pump signal to the gain medium, wherein the at least one pump signal interacts with the at least one optical signal as the at least one pump signal traverses at least a portion of the gain medium.

15. The method of claim 14 , wherein the gain medium is substantially free from optical components that require electrical power.

16. The method of claim 14 , wherein the at least one pump signal co-propagates with the optical signal over at least a portion of the gain medium.

17. The method of claim 14 , wherein the at least one pump signal counter-propagates with the optical signal over at least a portion of the gain medium.

18. The system of claim 1 , wherein the one or more pump sources comprise:

a first pump source capable of generating at least the second pump signal that co-propagates within the gain medium with at least a portion of the optical signal, the second pump signal comprising the plurality of fractional Raman order pump wavelengths having a Raman gain peak that is a non-integer multiple of one stokes shift from each of the one or more optical signal wavelengths; and

a second pump source capable of generating at least the first pump signal that counter-propagates within the gain medium with at least a portion of the optical signal, the first pump signal comprising the plurality of integer Raman order pump wavelengths having a Raman gain peak that is one stokes shift from at least one of the one or more optical signal wavelengths, wherein at least one of the one or more fractional Raman order pump wavelengths operates to amplify at least one of the one or more integer Raman order pump wavelengths as the pump signal traverses the transmission fiber.

19. The system of claim 8 , wherein the one or more pump sources comprise:

a first pump source capable of generating at least the second pump signal that co-propagates within the gain medium with at least a portion of the optical signal, the second pump signal comprising the plurality of fractional Raman order pump wavelengths comprising a Raman gain peak that is a non-integer multiple of one stokes shift from all of the plurality of optical signal wavelengths, wherein the non-integer multiple of one stokes shift from all of the plurality of optical signal wavelengths is greater than 1.1 stokes shifts and less than 1.9 stokes shifts from all of the plurality of optical signal wavelengths; and

a second pump source capable of generating at least the first pump signal that counter-propagates within the gain medium with at least a portion of the optical signal, the first pump signal comprising the plurality of integer Raman order pump wavelengths having a Raman gain peak that is one stokes shift from at least one of the one or more optical signal wavelengths, wherein at least one of the plurality of fractional Raman order pump wavelengths operates to amplify at least one of the plurality of integer Raman order pump wavelengths as the pump signal traverses the transmission fiber.

20. The method of claim 14 , wherein at least one of the plurality of fractional Raman order pump wavelengths operates to amplify at least one of the plurality of integer Raman order pump wavelengths as the pump signal traverses the transmission fiber.