Claims
- 1. A method of correcting for polarization mode dispersion in a light signal having at least one communication channel, the method comprising:
(a) determining polarization states of the light signal at a plurality of frequency subbands in the communication channel; (b) determining a characteristic polarization mode dispersion vector using the determined polarization states; (c) determining a characteristic differential group delay; and (d) determining, from the characteristic differential group delay, at least two compensation settings which, when applied to the light signal, renders the polarization states of the light signal across the plurality of frequency subbands in the communication channel substantially equal.
- 2. The method of claim 1 wherein the determined polarization states are Stokes vectors.
- 3. The method of claim 1 wherein the determined polarization states are Jones vectors.
- 4. The method of claim 1 further comprising:
(e) applying the determined compensation settings to the light signal using a corresponding number of compensation stages.
- 5. The method of claim 1 wherein step (b) comprises:
(b-1) constructing a set of vectors from the determined polarization states.
- 6. The method of claim 5 wherein step (b) further comprises:
(b-2) constructing a set of frequency-dependent polarization mode dispersion vectors from the constructed vectors of step (b-1).
- 7. The method of claim 6 wherein step (b) further comprises:
(b-3) determining the characteristic polarization mode dispersion vector from the vectors of step (b-2).
- 8. The method of claim 7 wherein the characteristic polarization mode dispersion vector substantially satisfies a least-squares fit to the determined vectors of step (b-2).
- 9. The method of claim 1 wherein step (c) comprises:
(c-1) determining the characteristic differential group delay using a second-order fit to the determined polarization states of the light as a function of frequency.
- 10. The method of claim 1 wherein step (c) comprises:
(c-1) determining the differential group delay using the magnitude of the characteristic polarization mode dispersion vector.
- 11. The method of claim 1 wherein step (d) comprises:
(d-1) selecting a target polarization state value; and (d-2) determining the compensation settings such that, when the compensation settings are applied to the light signal, the difference between the selected target polarization state value and the polarization states of the light across the plurality of frequency subbands in the communication channel is substantially reduced.
- 12. The method of claim 11 wherein the selected target polarization state value is the polarization state value at the band center frequency.
- 13. The method of claim 1 wherein at least one of the compensation settings varies in magnitude.
- 14. The method of claim 1 wherein step (d) comprises:
(d-1) retrieving at least one compensation setting using the results of steps (b) and (c) from a memory comprising predetermined compensation settings.
- 15. The method of claim 14 wherein step (d) further comprises:
(d-2) utilizing the at least one retrieved compensation setting as an input to an optimization routine; and (d-3) using the result of the optimization routine as at least one of the compensation settings.
- 16. The method of claim 15 wherein the optimization routine is the Levenberg-Marquardt algorithm.
- 17. The method of claim 4 wherein step (e) comprises:
(e-1) computing rotation Mueller matrices for polarization controllers corresponding to the determined compensation settings.
- 18. The method of claim 1 wherein steps (a)-(d) are applied to a plurality of communication channels in the light signal at substantially the same time.
- 19. An apparatus for correcting polarization mode dispersion in a light signal having at least one communication channel, the apparatus comprising:
a polarization state detector for receiving the light signal and providing polarization state measurements thereof at a plurality of frequency subbands in the communication channel; a first compensator for receiving the light signal and imposing a first differential group delay thereon; and a second compensator for receiving the light signal from the first compensator and imposing a second differential group delay thereon, wherein the first differential group delay and the second differential group delay are determined from the polarization state measurements so as to reduce the polarization mode dispersion effects on the light signal.
- 20. The apparatus of claim 19 wherein at least one of the first and second compensators comprises:
a plurality of polarization controllers, each of the polarization controllers being associated with a particular communication channel.
- 21. The apparatus of claim 20 further comprising:
a demultiplexer in series with the plurality of polarization controllers; a multiplexer in series with the plurality of polarization controllers; and a common delay line in series with the multiplexer.
- 22. The apparatus of claim 21 wherein the common delay line is a polarization-maintaining fiber.
- 23. The apparatus of claim 22 wherein the common delay line comprises a free space delay including a first polarizing beam splitter, a second polarizing beam splitter, a first mirror, and a second mirror.
- 24. The apparatus of claim 22 wherein the common delay line includes a first collimator, a second collimator, and a birefringent crystal situated between the first collimator and the second collimator.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of co-pending U.S. Provisional Application No. 60/325,422, filed on Sep. 27, 2001, the entire disclosure of which is incorporated by reference as if set forth in its entirety herein.
Provisional Applications (1)
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Number |
Date |
Country |
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60325422 |
Sep 2001 |
US |