Digital demodulator architecture

1. A digital demodulator device for received optical signals, the digital demodulator comprising:

a quadrature error filter module configured to:

receive a digitized version of an optical signal; and

remove quadrature errors to generate a corrected series of data samples;

a frequency offset removal module configured to perform frequency rotation on the corrected series of data samples to generate a frequency corrected series of data samples;

a chromatic dispersion compensation module configured to remove, from the frequency corrected series of data samples, chromatic dispersion from horizontal and vertical polarization channels;

a matched filter decimator configured to implement an interpolation function that provides decimation on samples taken at substantially two+ε times the symbol rate;

a polarization mode dispersion (PMD)/polarization dependent loss (PDL) compensation module configured to compensate the frequency corrected series of data samples for interference caused by PMD and PDL; and

a phase recovery module configured to track and correct phase for the frequency corrected series of data samples.

2. The device of claim 1 , wherein the quadrature error filter is configured to receive the digitized version of an optical signal by receiving four parallel streams comprising a horizontal in-phase stream, a vertical in-phase stream, a horizontal quadrature stream, and a vertical in-phase stream.

3. The device of claim 1 , wherein the quadrature error filter is configured to remove quadrature errors by:

detecting and removing a skew between in-phase and quadrature components.

4. The device of claim 1 , wherein the quadrature error filter is configured to remove quadrature errors by:

detecting and removing direct current bias.

5. The device of claim 1 , wherein the quadrature error filter is configured to remove quadrature errors by:

detecting and removing in-phase and quadrature amplitude imbalance.

6. The device of claim 1 , wherein the quadrature error filter is configured to remove quadrature errors by:

detecting and removing in-phase and quadrature phase imbalance.

7. The device of claim 1 , wherein the quadrature error filter is configured to remove quadrature errors of the optical signal before it is received by the frequency offset removal module.

8. The device of claim 1 , further comprising:

a carrier frequency acquisition and tracking module configured to calculate a frequency error metric for feedback to the frequency offset removal module.

9. The device of claim 8 , wherein,

the carrier frequency acquisition and tracking module processes the optical signal after the PMD/PDL compensation module compensates for interference caused by PMD and PDL; and

the frequency offset removal module performs the rotation using the frequency error metric.

10. The device of claim 1 , further comprising:

a carrier frequency acquisition and tracking module configured to calculate a filtered frequency error metric for controlling a local oscillator.

11. The device of claim 1 , further comprising:

a symbol timing acquisition and tracking module configured to perform symbol timing acquisition and tracking of the optical signal after the PMD/PDL compensation module compensates for interference caused by PMD and PDL and before carrier phase recovery on the optical signal.

12. The device of claim 1 , further comprising:

a frame synchronization module configured to skew, swap, and rotate received channels with respect to each other.

13. The device of claim 1 , further comprising:

a differential decoder configured to differentially decode a demodulated optical signal and provide the decoded output to the frame synchronization module.

14. The device of claim 1 , wherein the demodulated signal comprises hard decision or soft decision data.

15. The device of claim 1 , wherein the device comprises a processor.

16. A system comprising:

means for receiving a digitized version of an optical signal;

means for removing quadrature errors to generate a corrected series of data samples;

means for performing frequency rotation on the corrected series of data samples to generate a frequency corrected series of data samples;

means for removing, from the frequency corrected series of data samples, chromatic dispersion from horizontal and vertical polarization channels of a processed version of the optical signal;

means for implementing an interpolation function that provides decimation on samples taken at substantially two+ε times the symbol rate;

means for compensating for interference caused by polarization mode dispersion (PMD) and polarization dependent loss (PDL); and

means for tracking and correcting phase.

17. A method comprising:

receiving a digitized version of an optical signal;

removing quadrature errors to generate a corrected series of data samples;

performing frequency rotation on the corrected series of data samples to generate a frequency corrected series of data samples;

removing chromatic dispersion from horizontal and vertical polarization channels;

implementing an interpolation function that provides decimation on samples taken at substantially two+ε times the symbol rate;

compensating, after performing frequency rotation, the frequency corrected series of data samples for interference caused by polarization mode dispersion (PMD) and polarization dependent loss (PDL); and

tracking and correcting phase.

18. The method of claim 17 , wherein the receiving the digitized version of the optical signal comprises:

receiving four parallel streams comprising a horizontal in-phase stream, a vertical in-phase stream, a horizontal quadrature stream, and a vertical in-phase stream.

19. The method of claim 17 , wherein the removing the quadrature errors comprises:

detecting and removing a skew between in-phase and quadrature components.

20. The method of claim 17 , wherein the removing the quadrature errors comprises:

detecting and removing direct current bias.

21. The method of claim 17 , wherein the removing the quadrature errors comprises:

detecting and removing in-phase and quadrature amplitude imbalance; and

detecting and removing in-phase and quadrature phase imbalance.

22. The method of claim 17 , wherein the removing the quadrature errors for the optical signal occurs before the performing frequency rotation on the optical signal.

23. The method of claim 17 , further comprising:

calculating a frequency error metric for a PMD and PDL compensated version of the optical signal; and

feeding back the frequency error metric for use during the performing frequency rotation.

24. The method of claim 17 , further comprising:

calculating a filtered frequency error metric for a PMD and PDL compensated version of the optical signal; and

providing the filtered frequency error metric to a local oscillator.

25. The method of claim 17 , further comprising:

performing symbol timing acquisition and tracking on the optical signal after the compensation for the PMD/PDL compensation module compensates for interference caused by PMD and PDL and before carrier phase recovery.

26. The method of claim 17 , further comprising:

differentially decoding a demodulated optical signal and providing hard decoded output; and

synchronizing received channels of the hard decoded output with respect to each other.