Inter-band cross-phase modulation compensation for the mitigation of intra-channel nonlinear impairments in optical fiber transmission

1. An optical communication system comprising:

a transmitter;

an optical link coupled to the transmitter;

a coherent receiver coupled to the optical link for receiving a signal; and

a digital signal processor coupled to the coherent receiver, including a nonlinearity compensation module for compensating for nonlinear effects in fiber in the optical link for increasing capacity or transmission distance of the fiber, the nonlinearity compensation module includes a spectral slicing of the signal into bands, computing nonlinear interaction between the bands with intra-channel and intra-band parameters opposite to those of the fiber to reverse the non-linear effects in the fiber, and only certain nonlinear interactions between bands are considered thereby reducing complexity of nonlinearity compensation.

2. The system of claim 1 , wherein the digital signal processor comprises digitizing and re-sampling the signal to provide time domain signals expressed as X (t) and Y (t) for x and y polarizations respectively with X (t) and Y (t) being transformed into multiple bands by sharp filtering in a frequency domain.

3. The system of claim 1 , wherein digital filters are used to cut an original spectrum of the signal to create the bands and then a linear operator performs chromatic dispersion CD compensation to each band, the CD compensation being performable in either in a frequency domain using a transform pair in the frequency domain or using FIR filters in time domain.

4. The system of claim 1 , wherein the nonlinearity compensation comprises performing a convolution between nonlinearity bands with impulse responses, the convolution can be performed using finite impulse response filters FIR in a time domain, coefficients of the impulse response filters being obtained by performing inverse fast Fourier (IFFT) transform of the impulse response filters which depend on a chromatic dispersion of the optical link through walk-off parameters, and values of the filters are static and can be stored in a memory location so they do not have to be calculated every time.

5. The system of claim 1 , wherein the nonlinearity compensation comprises the signal being sliced into bands in a frequency domain where digital filters are used to cut an original spectrum create the bands, then a linear operator performs chromatic dispersion CD compensation to each band, the CD compensation being performable in a frequency domain using a fast Fourier transform and inverse fast fourier transform FFT/IFFT pair or in a time domain using finite impulse response FIR filters.

6. The system of claim 1 , wherein the amount of dispersion to be compensated depends on an optical link and a number of stages, in dispersion unmanaged links, an amount of chromatic dispersion compensation CDC per stage being a total CD of the optical link divided by the number of stages and in dispersion managed links, the amount of CDC per stage is a residual CD of a link divided by the number of stages.

7. A method for an optical communication system comprising the steps of:

transmitting a signal from a transmitter;

coupling an optical link to the transmitter;

coupling a coherent receiver to the optical link for receiving a signal; and

employing a digital signal processing coupled to the coherent receiver for providing a nonlinearity compensation module for nonlinear effects in fiber in the optical link thereby increasing capacity or transmission distance of the fiber, a nonlinearity compensation including a spectral slicing of the signal into bands by computing nonlinear interaction between the bands with intra-channel and intra-band parameters opposite to those of the fiber to reverse the non-linear effects in the fiber, and only certain nonlinear interactions between bands being considered thereby reducing complexity of nonlinearity compensation.

8. The method of claim 7 , wherein the digital signal processing comprises digitizing and re-sampling the signal to provide time domain signals expressed as X (t) and Y (t) for x and y polarizations respectively with X (t) and Y (t) being transformed into multiple bands by sharp filtering in a frequency domain.

9. The method of claim 7 , wherein the digital signal processing comprises employing digital filters for cutting an original spectrum of the signal to create the bands and then performing with a linear operator chromatic dispersion CD compensation to each band, the CD compensation being performable in either in a frequency domain using a transform pair in the frequency domain or using FIR filters in time domain.

10. The method of claim 7 , wherein the nonlinearity compensation comprises performing a convolution between nonlinearity bands with impulse responses, the convolution being performable using finite impulse response filters FIR in a time domain, coefficients of the impulse response filters being obtained by performing an inverse fast Fourier (IFFT) transform of the impulse response filters which depend on a chromatic dispersion of the optical link through walk-off parameters, values of the filters being static and storable in a memory location so they do not have to be calculated every time.

11. The method of claim 7 , wherein the nonlinearity compensation comprises the slicing the signal into bands in a frequency domain where digital filters are used to cut an original spectrum create the bands, then a linear operator performing chromatic dispersion CD compensation to each band, the CD compensation being performable in a frequency domain using a fast Fourier transform and inverse fast fourier transform FFT/IFFT pair or in a time domain using finite impulse response FIR filters.

12. The method of claim 7 , wherein an amount of dispersion to be compensated depends on the optical link and a number of stages, wherein in dispersion unmanaged links the amount of chromatic dispersion compensation CDC per stage being a total CD of the optical link divided by the number of stages and in dispersion managed links an amount of CDC per stage being a residual CD of a link divided by the number of stages.