Sub-Sampled Carrier Phase Recovery

1. A method comprising: obtaining a plurality of consecutive symbols associated with an optical signal received at an optical receiver; performing carrier phase recovery of the optical signal using one or more carrier phase estimation stages to generate a phase recovered signal; and at each of the one or more carrier phase estimation stages, selecting a subset of the plurality of consecutive symbols for use in carrier phase estimation, wherein the subset of symbols selected for use in carrier phase estimation at each of the one or more stages comprises one or more symbols having a highest ratio of measured signal phase error to additive noise.

2. The method of claim 1 , wherein performing carrier phase recovery of the optical signal using one or more carrier phase estimation stages comprises: performing carrier phase recovery using a Viterbi-Viterbi carrier phase estimation stage to generate Viterbi-Viterbi phase error corrected symbols.

3. The method of claim 2 , wherein selecting a subset of the plurality of symbols for carrier phase estimation comprises: performing ring partitioning of the symbols to determine within which of a first, second, or third constellation radius ring each of the symbols falls; organizing the plurality of symbols into a plurality of groups of symbols consecutive in time; discarding any symbols which fall in the second ring and are not usable in a 4 th -power function; and selecting, from the symbols remaining in each of the plurality of groups, a symbol that has the highest ratio between measured signal phase error and additive noise.

4. The method of claim 2 , wherein performing carrier phase recovery of the optical signal using one or more carrier phase estimation stages comprises: performing carrier phase recovery using a Maximum-Likelihood carrier phase estimation stage, wherein the Maximum-Likelihood carrier phase estimation stage operates using a subset of the Viterbi-Viterbi phase error corrected symbols.

5. The method of claim 4 , wherein selecting a subset of the plurality of symbols for carrier phase estimation comprises: organizing the plurality of Viterbi-Viterbi phase error corrected symbols into a plurality of groups of symbols consecutive in time; and selecting, from each of the plurality of groups of Viterbi-Viterbi phase error corrected symbols, a symbol with the highest ratio between measured signal phase error and additive noise.

6. The method of claim 4 , wherein selecting a subset of the plurality of symbols for carrier phase estimation comprises: organizing the plurality of Viterbi-Viterbi phase error corrected symbols into a plurality of groups; discarding any Viterbi-Viterbi phase error corrected symbols for which a precursor of the Viterbi-Viterbi phase error corrected symbols was used in the Viterbi-Viterbi carrier phase estimation stage; and selecting, from the one or more symbols remaining in each of the plurality of groups of Viterbi-Viterbi phase error corrected symbols, a Viterbi-Viterbi phase error corrected symbol with the highest ratio between the measured signal phase error and additive noise.

7. The method of claim 1 , further comprising: decoding the phase recovered signal with a forward error correction decoder.

8. An apparatus comprising: a phase recovery module configured to perform carrier phase estimation using one or more stages; and sub-sampling logic configured to receive a plurality of consecutive symbols associated with an optical signal and configured to select a subset of the plurality of consecutive symbols for use in carrier phase estimation to obtain a phase recovered signal, wherein the subset of symbols selected for use in carrier phase estimation at each of the one or more stages comprise one or more symbols having a highest ratio of measured signal phase error to additive noise.

9. The apparatus of claim 8 , wherein the phase recovery module comprises a Viterbi-Viterbi carrier phase estimation stage configured to generate Viterbi-Viterbi phase error corrected symbols.

10. The apparatus of claim 9 , wherein the sub-sampling logic is configured to: perform ring partitioning of the symbols to determine within which of a first, second, or third constellation radius ring each of the symbols falls; organize the plurality of symbols into a plurality of groups of symbols consecutive in time; discard any symbols which fall in the second ring and are not usable in a 4 th -power function; and select, from the symbols remaining in each of the plurality of groups, a symbol that has the highest ratio between measured signal phase error and additive noise.

11. The apparatus of claim 9 , wherein the phase recovery module further comprises a Maximum-Likelihood carrier phase estimation stage, wherein the Maximum-Likelihood carrier phase estimation stage operates using a subset of the Viterbi-Viterbi phase error corrected symbols.

12. The apparatus of claim 11 , wherein the sub-sampling logic is configured to: organize the plurality of Viterbi-Viterbi phase error corrected symbols into a plurality of groups of symbols consecutive in time; and select, from each of the plurality of groups of Viterbi-Viterbi phase error corrected symbols, a symbol with the highest ratio between measures signal phase error and additive noise.

13. The apparatus of claim 11 , wherein the sub-sampling logic is configured to: organize the plurality of Viterbi-Viterbi phase error corrected symbols into a plurality of groups; discard any Viterbi-Viterbi phase error corrected symbols for which a precursor of the Viterbi-Viterbi phase error corrected symbols was used in the Viterbi-Viterbi carrier phase estimation stage; and select, from the one or more symbols remaining in each of the plurality of groups of Viterbi-Viterbi phase error corrected symbols, a Viterbi-Viterbi phase error corrected symbol with the highest ratio between the measured signal phase error and additive noise.

14. The apparatus of claim 8 , further comprising a forward error correction decoder configured to decode the phase recovered signal.

15. A method comprising: obtaining a plurality of consecutive symbols associated with an optical signal received at an optical receiver; grouping the plurality of consecutive symbols into a plurality of groups of symbols consecutive in time; and from each of the plurality of groups, selecting the symbol having a relative highest ratio between measured signal phase error and additive noise to generate a subset of received symbols; and performing carrier phase recovery at one or more carrier phase estimation stages using the subset of received symbols to obtain a phase recovered signal.

16. The method of claim 15 , wherein performing carrier phase recovery of the optical signal using one or more carrier phase estimation stages comprises: performing carrier phase recovery using a Viterbi-Viterbi carrier phase estimation stage to generate Viterbi-Viterbi phase error corrected symbols.

17. The method of claim 16 , wherein selecting the symbol having the relative highest ratio between the measured signal phase error and additive noise to generate a subset of received symbols comprises: performing ring partitioning of the symbols to determine within which of a first, second, or third constellation radius ring each of the symbols falls; organizing the plurality of symbols into the plurality of groups of symbols consecutive in time; and selecting, from each of the plurality of groups, a symbol that that has the highest ratio between the measured signal phase error and additive noise and is useable in a 4 th -power function.

18. The method of claim 16 , wherein performing carrier phase recovery of the optical signal using one or more carrier phase estimation stages comprises: performing carrier phase recovery using a Maximum-Likelihood carrier phase estimation stage, wherein the Maximum-Likelihood carrier phase estimation stage operates using a subset of the Viterbi-Viterbi phase error corrected symbols.

19. The method of claim 18 , further comprising: organizing the plurality of Viterbi-Viterbi phase error corrected symbols into a plurality of groups; discarding any Viterbi-Viterbi phase error corrected symbols for which a precursor of the Viterbi-Viterbi phase error corrected symbols was used in the Viterbi-Viterbi carrier phase estimation stage; and selecting, from the one or more symbols remaining in each of the plurality of groups of Viterbi-Viterbi phase error corrected symbols, a Viterbi-Viterbi phase error corrected symbol with the highest ratio between the measured signal phase error and additive noise.

20. The method of claim 15 , further comprising: decoding the phase recovered signal with a forward error correction decoder.