Estimation of communication system impairments using spectrally selective signal perturbations

1. An optical communication system comprising:

circuitry configured to generate a perturbed signal by perturbing an amplitude of a spectrum of an original signal in multiple spectral regions, wherein the perturbed signal has a same total power as the original signal;

circuitry configured to propagate the perturbed signal through components of the optical communication system;

circuitry configured to obtain a measurement of the perturbed signal in a first spectral region of the multiple spectral regions following the propagation of the perturbed signal; and

circuitry configured to calculate an estimate of an impairment associated with the optical communication system based on the measurement.

2. The optical communication system as claimed in claim 1 ,

wherein the components comprise components of a transmitter device and components of a spectrum measurement device (SMD) connected directly to the transmitter device, the transmitter device comprising the circuitry configured to generate the perturbed signal, and the SMD comprising the circuitry configured to obtain the measurement,

wherein the amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining the first spectral region,

wherein the measurement comprises a measurement of power of the perturbed signal in the first spectral region, and

wherein the impairment comprises a noise floor of the optical communication system in the first spectral region.

3. The optical communication system as claimed in claim 2 , further comprising

circuitry configured to generate additional versions of the perturbed signal, each additional version generated by attenuating the amplitude of the spectrum to substantially zero over a different contiguous set of frequencies defining a different spectral region of the spectrum;

circuitry configured to propagate each additional version of the perturbed signal through the components of the optical communication system at a different time;

circuitry configured to obtain an additional version of the measurement for each additional version of the perturbed signal following the propagation of the additional version; and

circuitry configured to calculate an additional estimate of the noise floor in each additional spectral region based on each additional version of the measurement.

4. The optical communication system as claimed in claim 2 , wherein the amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining a second spectral region of the multiple spectral regions, the communication system further comprising

circuitry configured to obtain a measurement of power of the perturbed signal in the second spectral region following the propagation of the perturbed signal; and

circuitry configured to calculate an estimate of a noise floor of the communication system in the second spectral region based on the measurement of the perturbed signal in the second spectral region.

5. The optical communication system as claimed in claim 2 , wherein the SMD comprises an optical spectrum analyzer or a coherent receiver.

6. The optical communication system as claimed in claim 1 , wherein the amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining the first spectral region, the optical communication system further comprising

circuitry configured to generate the perturbed signal by applying a phase perturbation to the spectrum in a second spectral region that is substantially symmetrically disposed relative to the first spectral region about a central frequency of the spectrum, wherein the phase perturbation comprises a function of frequency;

circuitry configured to generate additional versions of the perturbed signal, each additional version generated by applying a different phase perturbation, comprising a different function of frequency, to the spectrum in the second spectral region, and by attenuating the amplitude of the spectrum to substantially zero over the contiguous set of frequencies defining the first spectral region;

circuitry configured to propagate each additional version of the perturbed signal through the components of the optical communication system at a different time; and

circuitry configured to obtain an additional version of the measurement in the first spectral region for each additional version of the perturbed signal following the propagation of the additional version of the perturbed signal,

wherein the estimate of the impairment is calculated based on the additional versions of the measurement, and wherein the impairment comprises frequency-dependent phase offset.

7. The optical communication system as claimed in claim 1 ,

wherein the components comprise components of a transmitter device, components of a receiver device, and components of at least one optical communication channel between the transmitter device and the receiver device, the transmitter device comprising the circuitry configured to generate the perturbed signal, and the receiver device comprising the circuitry configured to obtain the measurement, and

wherein an amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining the first spectral region, wherein the amplitude is unperturbed over a contiguous set of frequencies defining a second spectral region, and wherein the amplitude is unperturbed over a contiguous set of frequencies defining a third spectral region,

the optical communication system further comprising

circuitry configured to generate additional versions of the perturbed signal, each additional version generated by enhancing the amplitude of the spectrum in the second spectral region and by attenuating the amplitude of the spectrum by a corresponding amount in the third spectral region, wherein each additional version is characterized by a different pair of amplitudes in the second and third spectral regions;

circuitry configured to propagate each additional version of the perturbed signal through the components of the optical communication system at a different time;

circuitry configured to obtain an additional version of the measurement for each additional version of the perturbed signal following the propagation of the additional version; and

circuitry configured to calculate the estimate of impairment based on the measurement and the additional versions of the measurement.

8. The optical communication system as claimed in claim 7 , wherein the optical communication system is configured for optical communication and wherein the components of the at least one optical communication channel comprise a plurality of spans, each span comprising an optical amplifier.

9. The optical communication system as claimed in claim 7 , wherein the impairment comprises amplified spontaneous emission (ASE) or intra-channel nonlinear noise or both.

10. The optical communication system as claimed in claim 7 , wherein the at least one optical communication channel comprises first and second wavelength division multiplexing (WDM) channels, wherein the perturbed signal and each additional version of the perturbed signal are propagated over the first WDM channel, and wherein the impairment comprises inter-channel nonlinear noise contributed by the second WDM channel to the first WDM channel.

11. A method comprising:

generating a perturbed signal by perturbing an amplitude of a spectrum of an original signal in multiple spectral regions, wherein the perturbed signal has a same total power as the original signal;

propagating the perturbed signal through components of an optical communication system;

obtaining a measurement of the perturbed signal in a first spectral region of the multiple spectral regions following the propagation of the perturbed signal; and

calculating an estimate of an impairment associated with the optical communication system based on the measurement.

12. The method as claimed in claim 11 ,

wherein the components comprise components of a transmitter device and components of a spectrum measurement device (SMD) connected directly to the transmitter device, the transmitter device configured to generate the perturbed signal, and the SMD configured to obtain the measurement,

wherein the amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining the first spectral region,

wherein the measurement comprises a measurement of power of the perturbed signal in the first spectral region, and

wherein the impairment comprises a noise floor of the optical communication system in the first spectral region.

13. The method as claimed in claim 12 , further comprising

generating additional versions of the perturbed signal, each additional version generated by attenuating the amplitude of the spectrum to substantially zero over a different contiguous set of frequencies defining a different spectral region of the spectrum;

propagating each additional version of the perturbed signal through the components of the optical communication system at a different time;

obtaining an additional version of the measurement for each additional version of the perturbed signal following the propagation of the additional version; and

calculating an additional estimate of the noise floor in each additional spectral region based on each additional version of the measurement.

14. The method as claimed in claim 12 , wherein the amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining a second spectral region of the multiple spectral regions, the method further comprising

obtaining a measurement of power of the perturbed signal in the second spectral region following the propagation of the perturbed signal; and

calculating an estimate of a noise floor of the optical communication system in the second spectral region based on the measurement of the perturbed signal in the second spectral region.

15. The method as claimed in claim 12 , wherein the SMD comprises an optical spectrum analyzer or a coherent receiver.

16. The method as claimed in claim 11 , wherein the amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining the first spectral region, the method further comprising

generating the perturbed signal by applying a phase perturbation to the spectrum in a second spectral region that is substantially symmetrically disposed relative to the first spectral region about a central frequency of the spectrum, wherein the phase perturbation comprises a function of frequency;

generating additional versions of the perturbed signal, each additional version generated by applying a different phase perturbation, comprising a different function of frequency, to the spectrum in the second spectral region, and by attenuating the amplitude of the spectrum to substantially zero over the contiguous set of frequencies defining the first spectral region;

propagating each additional version of the perturbed signal through the components of the optical communication system at a different time; and

obtaining an additional version of the measurement in the first spectral region for each additional version of the perturbed signal following the propagation of the additional version of the perturbed signal,

wherein the estimate of the impairment is calculated based on the additional versions of the measurement, and wherein the impairment comprises frequency-dependent phase offset.

17. The method as claimed in claim 11 ,

wherein the components comprise components of a transmitter device, components of a receiver device, and components of at least one optical communication channel between the transmitter device and the receiver device, the transmitter device configured to generate the perturbed signal, and the receiver device configured to obtain the measurement, and

wherein an amplitude of the spectrum is attenuated to substantially zero over a contiguous set of frequencies defining the first spectral region, wherein the amplitude is unperturbed over a contiguous set of frequencies defining a second spectral region, and wherein the amplitude is unperturbed over a contiguous set of frequencies defining a third spectral region,

the method further comprising

generating additional versions of the perturbed signal, each additional version generated by enhancing the amplitude of the spectrum in the second spectral region and by attenuating the amplitude of the spectrum by a corresponding amount in the third spectral region, wherein each additional version is characterized by a different pair of amplitudes in the second and third spectral regions;

propagating each additional version of the perturbed signal through the components of the optical communication system at a different time;

obtaining an additional version of the measurement for each additional version of the perturbed signal following the propagation of the additional version; and

calculating the estimate of impairment based on the measurement and the additional versions of the measurement.

18. The method as claimed in claim 17 , wherein the components of the at least one optical communication channel comprise a plurality of spans, each span comprising an optical amplifier.

19. The method as claimed in claim 17 , wherein the impairment comprises amplified spontaneous emission (ASE) or intra-channel nonlinear noise or both.

20. The method as claimed in claim 17 , wherein the at least one optical communication channel comprises first and second wavelength division multiplexing (WDM) channels, wherein the perturbed signal and each additional version of the perturbed signal are propagated over the first WDM channel, and wherein the impairment comprises inter-channel nonlinear noise contributed by the second WDM channel to the first WDM channel.