Band optical add/drop multiplexing

1. A multiple span optical communication system comprising:

at least one optical add/drop multiplexing (OADM) node operable to receive at least a first input band comprising a first plurality of signal wavelengths, at least a second input band comprising a second plurality of signal wavelengths, and at least one signal wavelength that is designated as a first guard-channel, wherein the first guard-channel is substantially free from being an information bearing channel, wherein each of the first plurality of signal wavelengths of the first input band is different than each of the second plurality of signal wavelengths of the second input band, wherein each of the first plurality of wavelengths and each of the second plurality of wavelengths received by the OADM is designated as an information bearing channel, and wherein the first guard-channel received by the OADM separates the first input band from the second input band, the at least one OADM further operable to communicate at least one output band and at least another signal wavelength that is designated as a second guard-channel that separates the at least one output band from other output bands, wherein the second guard-channel is substantially free from being an information bearing channel;

wherein at least one signal wavelength of the second plurality of signal wavelengths received by the OADM is designated as the second guard-channel communicated from the OADM, and wherein the at least one signal wavelength of the first guard-channel received by the OADM is designated as an information bearing channel in the at least one output band communicated from the OADM.

2. The multiple span optical communication system of claim 1 , wherein the second input band resides spectrally adjacent to the at least one signal wavelength that is designated as the first guard-channel, the first guard-channel operable to assist in protecting at least the second input band during communication between a first node and the at least one OADM node; and

wherein the at least one output band comprises at least some of the second plurality of wavelength signals of the second input band and the at least one signal wavelength of the at least one guard-channel redesignated to carry information between the at least one OADM node and a second node.

3. The multiple span optical communication system of claim 1 , wherein:

the second input band resides spectrally adjacent to the at least one signal wavelength that is designated as the first guard-channel, the first guard-channel operable to assist in protecting at least the second input band during communication between a first node and the at least one OADM node;

wherein the at least one signal wavelength that is designated as the first guard-channel resides spectrally adjacent to the first input band used to carry information between the first node and the at least one OADM node; and

wherein the at least one output signal band comprises at least some of the second plurality of wavelength signals of the second input band, the at least one signal wavelength of the at least one signal wavelength that is designated as the first guard-channel, and at least one signal wavelength from the first plurality of signal wavelengths of the first input band, designated to carry information between the at least one OADM node and a second node.

4. The multiple span optical communication system of claim 1 , further comprising:

a plurality of low distortion OADM nodes each coupled between spans of a multiple span communications link and operable to receive a multiple wavelength signal comprising a plurality of bands of wavelength signals each separated by at least one guard-channel;

wherein each of the plurality of low distortion OADM nodes adds/drops one or more bands of wavelengths to/from the multiple wavelength signal.

5. The multiple span optical communication system of claim 4 , wherein the plurality of low distortion OADM nodes comprises a tunable OADM operable to selectively add/drop one or more bands.

6. The multiple span optical communication system of claim 4 , wherein each band is separated from an adjacent band by at least two (2) guard-channels.

7. The multiple span optical communication system of claim 4 , wherein each low distortion OADM introduces to a pass-through wavelength signal spectrally adjacent to a guard-channel that is adjacent to the first input band an asymmetry penalty of no more than 1.0 decibels.

8. The multiple span optical communication system of claim 4 , wherein each low distortion OADM introduces to a pass-through wavelength signal spectrally adjacent to a guard-channel that is adjacent to the first input band an asymmetry penalty of no more than 0.3 decibels.

9. The multiple span optical communication system of claim 4 , wherein the plurality of low distortion OADMs introduces an asymmetry penalty of no more than two (2) decibels after exiting the last of the plurality of low distortion OADMs.

10. The multiple span optical communication system of claim 4 , wherein the plurality of low distortion OADMs collectively degrade a Q-factor associated with a pass-through wavelength signal spectrally adjacent to a guard-channel that is adjacent to the first input band by no more than 3.0 decibels.

11. The multiple span optical communication system of claim 4 , wherein the plurality of low distortion OADMs collectively degrade a Q-factor associated with a pass-through wavelength signal spectrally adjacent to a guard-channel that is adjacent to the first input band by no more than 0.5 decibels.

12. A multiple span optical communication system comprising:

at least one optical add/drop multiplexing (OADM) node operable to receive at least a first input band comprising a first plurality of signal wavelengths, a second input band comprising a second plurality of wavelengths, and at least one signal wavelength that is designated as a first guard-channel, wherein the first guard-channel is substantially free from being an information bearing channel, wherein each of the first plurality of signal wavelengths of the first input band is different than each of the second plurality of signal wavelengths of the second input band, wherein each of the first plurality of wavelengths and each of the second plurality of wavelengths received by the OADM is designated as an information bearing channel, and wherein the first guard-channel received by the OADM separates the first input band from the second input band, the at least one OADM further operable to communicate at least one output band and at least another signal wavelength that is designated as a second guard-channel that separates the at least one output band from other output bands, wherein the second guard-channel is substantially free from being an information bearing channel;

wherein the at least one output band communicated from the OADM comprises a third plurality of signal wavelengths that includes at least some of the first plurality of signal wavelengths and the at least one wavelength of the first guard-channel received by the OADM, wherein each of the third plurality of signal wavelengths of the output band is designated as an information bearing channel.

13. The multiple span optical communication system of claim 12 , wherein the at least one output band comprises:

a first output band comprising the second plurality of signal wavelengths, the second plurality of signal wavelengths comprising at least a first portion of the first plurality of signal wavelengths associated with the at least one input band; and

a second output band comprising a third plurality of signal wavelengths, the third plurality of signal wavelengths comprising at least a second portion of the first plurality of signal wavelengths associated with the at least one input band.

14. The multiple span optical communication system of claim 12 , wherein:

the first input band is associated with communications between a first node and the at least one OADM node;

the first output band is associated with communications between the at least one OADM node and a second node; and

the second output band is associated with communications between the at least one OADM node and a third node.

15. The multiple span optical communication system of claim 12 , wherein:

the first input band resides spectrally adjacent to the at least one signal wavelength that is designated as the first guard-channel, the first guard-channel operable to assist in protecting at least the first input signal band during communication between a first node and the at least one OADM node; and

wherein the at least one output band comprises the at least one guard-channel redesignated to carry information between the at least one OADM node and the second node.

16. The multiple span optical communication system of claim 12 , wherein the multiple span communications link comprises a length of at least 900 kilometers.

17. A method of communicating optical signals using a band optical add/drop multiplexer, comprising:

receiving a multiple wavelength signal comprising at least a first input band comprising a first plurality of signal wavelengths, a second input band comprising a second plurality of signal wavelengths, and at least one signal wavelength that is designated as a first guard-channel, wherein the first guard-channel is substantially free from being an information bearing channel, wherein each of the first plurality of signal wavelengths of the first input band is different than each of the second plurality of signal wavelengths of the second input band, wherein each of the first plurality of wavelengths and each of the second plurality of wavelengths received by the OADM is designated as an information bearing channel, and wherein the first guard-channel received by the OADM separates the first input band from the second input band; and

communicating at least one output band and at least another signal wavelength that is designated as a second guard-channel that separates the at least one output band from other output bands, wherein the second guard-channel is substantially free from being an information bearing channel;

wherein at least one signal wavelength of the second plurality of signal wavelengths received by the OADM is designated as the second guard-channel communicated from the OADM, and wherein the at least one signal wavelength that is designated as the first guard-channel received by the OADM is designated as an information bearing channel in the at least one output band communicated from the OADM.

18. The method of communicating of claim 17 , wherein:

the second input band is associated with communications between a first node and at least one OADM node; and

wherein the at least one output band is associated with communications between the at least one OADM node and a second node.

19. The method of communicating of claim 17 , wherein:

the second input band resides spectrally adjacent to the at least one signal wavelength that is designated as the first guard-channel, the first guard-channel operable to assist in protecting at least the second input band during communication between a first node and at least one OADM node; and

wherein the at least one output band comprises at least some of the second plurality of wavelength signals of the second input band and the at least one signal wavelength that is designated as the first guard-channel redesignated to carry information between the at least one OADM node and a second node.

20. The method of communicating of claim 17 , wherein:

the second input band resides spectrally adjacent to the at least one signal wavelength that is designated as the first guard-channel, the first guard-channel operable to assist in protecting at least the second input band during communication between the first node and the at least one OADM node;

wherein the first guard-channel resides spectrally adjacent to the first input band used to carry information between the first node and the at least one OADM node; and

wherein the at least one output signal band comprises at least some of the second plurality of wavelength signals of the second input band, the at least one signal wavelength that is designated as the first guard-channel, and at least one signal wavelength from the first plurality of signal wavelengths of the first input band, redesignated to carry information between the at least one OADM node and a second node.