Optical dispersion compensation

1. A method comprising:

determining an amount of current dispersion (D Cn ) contributed by a current span (n) of an optical network to a first channel of a multi-channel optical signal following an optical path;

determining a prior accumulated dispersion (D ACCn ) representing accumulated dispersion contributed by prior spans of the optical network along the optical path;

computing a total dispersion (D Tn ), wherein D Tn =D Cn +D ACCn ; and

controlling a dispersion compensator in accordance with the total dispersion to optically compensate the multi-channel optical signal at a compensation point on the current span, wherein the dispersion compensator comprises a plurality of cascaded single channel compensators.

2. The method of claim 1 wherein the multi-channel signal is carried by an optical fiber.

3. The method of claim 2 comprising:

tapping the optical fiber to provide a tapped optical signal.

4. The method of claim 3 comprising:

measuring the amount of current dispersion from the tapped optical signal.

5. The method of claim 2 comprising:

estimating a length (L) of the optical fiber from a propagation time of a signal communicated between a first network element and a second network element coupled by the optical fiber; and

estimating D Cn from the length L and a pre-determined dispersion characteristic D λ of the optical fiber.

6. The method of claim 3 comprising:

measuring a difference in propagation times for distinct spectral components of a signal communicated on a first channel of the tapped optical signal.

7. The method of claim 1 wherein D Tn corresponds to an amount of chromatic dispersion.

8. The method of claim 1 wherein the first channel is a supervisory channel.

9. The method of claim 1 wherein the dispersion compensator is controlled continuously or at pre-determined intervals of time to provide the optical compensation.

10. The method of claim 1 wherein the optical dispersion compensation is provided without interruption of the multi-channel optical signal.

11. An apparatus comprising:

a dispersion calculator determining an amount of current dispersion (D Cn ) contributed by a current span (n) of an optical network to at least one channel of a multi-channel optical signal following an optical path, wherein the dispersion calculator determines a prior accumulated dispersion (D ACCn ) representing accumulated dispersion contributed by prior spans of the optical network along the optical path, wherein the dispersion calculator computes a total dispersion signal D Tn =D Cn +D ACCn representing an amount of dispersion associated with at least one channel of a multi-channel optical signal; and

a compensator controlled in accordance with the total dispersion signal to optically compensate for total dispersion of the multi-channel optical signal, wherein the compensator comprises a plurality of cascaded single channel compensators.

12. The apparatus of claim 11 further comprising:

a tap coupled to provide a tapped optical signal including the at least one channel from the multi-channel optical signal;

a detector measuring a difference in propagation times for individual spectral components of the tapped optical signal to detect an amount of dispersion associated with the at least one channel, wherein the detector provides the detected dispersion as D Cn .

13. The apparatus of claim 11 wherein the optical signal is carried by an optical fiber.

14. The apparatus of claim 11 wherein D Cn represents an estimated amount of current dispersion, wherein D Cn is computed from a length L and a pre-determined dispersion characteristic D λ of the current span.

15. The apparatus of claim 11 wherein D ACCn is retrieved from a supervisory channel of the multi-channel optical signal.

16. The apparatus of claim 11 wherein D Tn represents a total amount of chromatic dispersion.

17. The apparatus of claim 11 wherein the compensator is controlled continuously or at pre-determined intervals of time to provide the optical compensation.

18. The apparatus of claim 11 wherein the at least one channel is a supervisory channel.

19. The apparatus of claim 11 wherein the compensator is controlled to optically compensate the multi-channel optical signal without interruption of the multi-channel optical signal.