Digital signal-to-signal beat noise reduction for filter-less coherent receiving system
View Patent ↗Systems and methods are disclosed for a filter-less coherent receiving system with a filter-less coherent receiver frontend; a signal-signal beat-noise detector coupled to the filter-less coherent receiver frontend; and a real-time processor coupled to the filter-less coherent receiver frontend and the signal-signal beat-noise detector to reject signal-signal interference.
1. A filter-less coherent receiving system, comprising
a. a filter-less coherent receiver frontend;
b. a signal-signal beat-noise detector coupled to the filter-less coherent receiver frontend; and
c. a real-time processor coupled to the filter-less coherent receiver frontend and the signal-signal beat-noise detector to reject signal-signal interference.
2. The system of claim 1 , comprising a digital signal processor (DSP) coupled to the real-time processor for data recovery.
3. The system of claim 1 , wherein the filter-less coherent receiver frontend comprises a ninety degree optical hybrid coupled to a local oscillator and a polarization maintaining (PM) coupler.
4. The system of claim 3 , comprising a plurality of photodiodes coupled to the ninety degree optical hybrid.
5. The system of claim 4 , comprising an analog to digital converter coupled to each photodiode.
6. The system of claim 1 , wherein the signal-signal beat-noise detector comprises a polarization beam splitter (PBS).
7. The system of claim 6 , comprising a plurality of photodiodes coupled to the PBS and an analog to digital converter coupled to each photodiode.
8. The system of claim 1 , wherein the real-time processor comprises a plurality of digital resampling blocks.
9. The system of claim 8 , wherein the direct detected signal-signal beat-noise is used to cancel interference terms at the coherent receiving system output by digital signal subtraction.
10. The system of claim 8 , wherein weighting coefficients and their exact timing relative to I_x, Q_x, I_y, and Q_y are a fixed set of values adjusted during system startup calibration.
11. A method to provide digital signal-to-signal beat noise reduction in a filter-less coherent receiving system, comprising:
a. receiving data at a filter-less coherent receiver frontend;
b. performing signal-signal beat-noise detection; and
c. performing real-time signal-signal interference rejection.
12. The method of claim 11 , comprising rejecting signal-signal beat noise using digital signal cancellation.
13. The method of claim 11 , comprising detecting signal-signal beating term.
14. The method of claim 13 , comprising using PM components for optical signal routing to maintain reference as the coherent receiver.
15. The method of claim 14 , comprising using a PBS to obtain signal-signal beating term on x and y polarization.
16. The method of claim 11 , comprising providing dedicated channels to detect the beating term.
17. The method of claim 16 , comprising using the same photodiode as a coherent receiver to match response.
18. The method of claim 16 , comprising fixing a converter sampling clock as a coherent receiver to minimize timing walk-offs.
19. The method of claim 11 , comprising digitally subtracting coherent receiver output and direct detection output to reject signal-signal interference.
20. The method of claim 19 , comprising performing start-up calibration of weighting coefficients and adjustment of timing skew to optimize performance.
21. The method of claim 11 , comprising sharing signal-signal beating term among WDM channels.
22. A method to provide digital signal-to-signal beat noise reduction in a filter-less coherent receiving system, comprising:
splitting an incoming wavelength-division multiplexing (WDM) optical signal into two paths provided as inputs to a coherent receiver and a signal-signal interference (SSI) detection receiver, wherein the optical signal has one polarization reference for the coherent receiver and the SSI detection receiver;
digitizing four signal components of the coherent receiver;
separating the SSI signal into separate SSI X and Y polarization with a polarization beam splitter (PBS) and digitizing the SSI X and Y polarizations; and
performing digital SSI suppression by subtracting the SSI X and Y polarizations from the signal components received by the coherent receiver.
23. The method of claim 22 , comprising adjusting weighting coefficients and timing offsets by performance feedbacks during digital signal processing.
24. The method of claim 22 , comprising processing signal components for data recovery after digital SSI suppression.