Characterization of non-ASE noise on optical signals

1. A method for determining a noise parameter characterizing an optical signal-under-test having a signal contribution, an Amplified Spontaneous Emission (ASE) noise contribution and a non-ASE optical noise contribution within an optical-signal bandwidth, wherein said signal contribution is polarized and wherein said non-ASE optical noise contribution comprises a depolarized-signal contribution, said method comprising:

acquiring, for each of a number nSOP of varied state-of-polarization analysis conditions of the signal-under-test, at least one polarization-analyzed optical spectrum trace using an optical spectrum analyzer;

using a spectrum processor, discriminating at least said non-ASE optical noise contribution from said ASE-noise contribution using at least one of the at least one polarization-analyzed optical spectrum trace and a trace obtained from the at least one polarization-analyzed optical spectrum trace;

using a noise calculator, determining said noise parameter characterizing said signal-under-test using at least one of the discriminated non-ASE optical noise contribution and the discriminated ASE-noise contribution; and

outputting said noise parameter;

further comprising: determining an extrema trace from the at least one polarization-analyzed optical spectrum trace;

wherein said discriminating is made using said extrema trace.

2. The method as claimed in claim 1 , wherein said discriminating is based on known different spectral-shape properties between said non-ASE optical noise contribution and said ASE-noise contribution.

3. The method as claimed in claim 2 , wherein said discriminating comprises discriminating at least said non-ASE optical noise contribution from said ASE-noise contribution and said signal contribution based on known different spectral-shape properties between said non-ASE optical noise contribution, said ASE-noise contribution and said signal contribution.

4. The method as claimed in claim 1 , wherein said non-ASE optical noise contribution comprises at least a carrier-leakage contribution.

5. The method as claimed in claim 1 , wherein said signal contribution comprises a data-carrying signal contribution.

6. The method as claimed in claim 1 , wherein the signal-under-test is a non-data-carrying probe optical signal as propagated over an optical communication channel to be characterized, said signal contribution comprising a probe signal contribution and characterization of said noise parameter on said signal-under-test provides a characterization of said optical communication channel.

7. The method as claimed in claim 1 , wherein said discriminating comprises discriminating at least said depolarized-signal contribution from said ASE-noise contribution in said extrema trace based on known different spectral-shape properties between said depolarized-signal contribution and said ASE-noise contribution.

8. The method as claimed in claim 1 , wherein said extrema trace is a composite extrema trace obtained by selecting, for each wavelength individually, an extrema value among said optical spectrum traces.

9. The method as claimed in claim 8 , wherein said composite extrema trace is a constructed composite extrema trace obtained by a normalization of a total optical spectrum trace of said signal-under-test using an extrema trace.

10. The method as claimed in claim 1 , wherein said depolarized-signal contribution comprises a Non-Linear-Effect-induced (NLE-induced) signal depolarization part and a Polarization-Mode-Dispersion-related (PMD-related) signal depolarization part, and wherein said method comprises:

estimating said PMD-related signal depolarization part from a PMD parameter indicative of a PMD-related signal depolarization part in said signal-under-test; and

estimating said NLE-induced signal depolarization part using the discriminated depolarized-signal part and the estimated PMD-related signal depolarization part;

wherein said noise parameter is determined using at least the estimated NLE-induced signal depolarization part.

11. The method as claimed in claim 10 , further comprising:

from the at least one polarization-analyzed optical spectrum trace, selecting a maximum trace and a minimum trace;

from the at least one polarization-analyzed optical spectrum trace, determining a composite extrema trace obtained by selecting, for each wavelength individually, an extrema value among the at least one polarization-analyzed optical spectrum trace; and

estimating said PMD-related signal depolarization part using a power-ratio spectral trace calculated from at least said maximum trace and said minimum trace and said composite extrema trace.

12. The method as claimed in claim 1 , wherein said depolarized-signal contribution comprises a Non-Linear-Effect-induced (NLE-induced) signal depolarization part, said method further comprising:

estimating said NLE-induced signal depolarization part on a first said optical signal-under-test using the discriminated depolarized-signal part; and

estimating a NLE-induced signal depolarization part on a second optical signal-under-test of a same wavelength-division-multiplexing communication link from the NLE-induced signal depolarization part as estimated on at least the first said optical signal-under-test.

13. The method as claimed in claim 1 , wherein, for each of said number nSOP of varied state-of-polarization analysis conditions of the signal under test, a pair of mutually orthogonal polarization-analyzed optical spectrum traces is acquired.

14. The method as claimed in claim 1 , wherein said noise parameter comprises an ASE-only Optical Signal-to-Noise Ratio (ASE-only OSNR).

15. The method as claimed in claim 1 , wherein said noise parameter comprises a signal-depolarization parameter.

16. A method for determining a noise parameter characterizing an optical signal-under-test having a signal contribution, a carrier-leakage contribution and an Amplified Spontaneous Emission (ASE-) noise contribution within an optical-signal bandwidth, said method comprising:

acquiring at least one optical spectrum trace of said signal-under-test using an optical spectrum analyzer;

using a spectrum processor, discriminating at least said carrier-leakage contribution from said ASE-noise contribution using at least one of said optical spectrum trace and a trace obtained from said at least one optical spectrum trace;

using a noise calculator, determining said noise parameter on said signal-under-test using at least one of the discriminated carrier-leakage contribution and the discriminated ASE-noise contribution; and

outputting said noise parameter;

wherein said acquiring comprises, for each of a number nSOP of varied state-of-polarization analysis conditions of the signal under test, the acquisition of at least one of said optical spectrum trace of said signal-under-test, wherein said optical spectrum trace is a polarization-analyzed optical spectrum trace;

further comprising: from the at least one polarization-analyzed optical spectrum trace, determining an extrema trace; and

wherein said discriminating is made using said extrema trace.

17. The method as claimed in claim 16 , wherein said discriminating comprises discriminating at least said carrier-leakage contribution from said ASE-noise contribution in said extrema trace based on known different spectral-shape properties between said carrier-leakage contribution and said ASE-noise contribution.

18. The method as claimed in claim 16 , wherein a spectral shape of said carrier-leakage contribution is known and wherein said discriminating comprises discriminating at least said carrier-leakage contribution from said ASE-noise contribution in said extrema trace using the known spectral shape of said carrier-leakage contribution.

19. The method as claimed in claim 16 , wherein said extrema trace is a minima trace.

20. The method as claimed in claim 19 , wherein said discriminating comprises performing an interpolation on said minima trace to estimate said ASE-noise contribution in said minima trace.

21. The method as claimed in claim 20 , wherein said interpolation is a linear interpolation.

22. The method as claimed in claim 19 , wherein said minima trace comprises a residual modulated signal contribution and wherein said method further comprises discriminating said carrier-leakage contribution from said residual modulated signal contribution and said ASE-noise contribution using a curve fit on said minima trace.

23. The method as claimed in claim 22 , wherein said curve fit fits a reference trace on said minima trace.

24. The method as claimed in claim 16 , wherein said extrema trace is a composite minima trace obtained by selecting, for each wavelength individually, a minima value among said optical spectrum traces.

25. The method as claimed in claim 16 , wherein, for each of said number nSOP of varied state-of-polarization analysis conditions of the signal under test, a pair of mutually orthogonal polarization-analyzed optical spectrum traces is acquired.

26. The method as claimed in claim 16 , wherein said noise parameter comprises a carrier-leakage parameter.

27. The method as claimed in claim 16 , wherein said noise parameter comprises an ASE-noise parameter.

28. The method as claimed in claim 16 , wherein said noise parameter comprises an ASE-only Optical Signal-to-Noise Ratio (ASE-only OSNR).

29. The method as claimed in claim 16 , wherein said noise parameter comprises a carrier-leakage extinction ratio.