De-emphasis Filtering for Raman Cross-talk Mitigation in PON
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Solution Overview
Problem
Raman cross-talk in passive optical network systems, particularly in next-generation gigabit PON systems, causes signal degradation and performance issues due to interference between different wavelength channels, leading to unacceptable bit error rates and service disruptions in video services.
Innovation Solution
Applying de-emphasis to the electrical modulation signal of the 1577 nm transmit laser to shape the downstream output optical data signal, reducing Raman cross-talk levels at critical video frequencies, and using digital or analog filtering to create a pulse-shaped signal that minimizes low-frequency interference, thereby enhancing the carrier-to-noise ratio, signal-to-noise ratio, and modulation error ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If XGPON-1 transmit power level is maintained at +12.5 dBm to achieve desired link budget and service distance, then data transmission performance is improved, but Raman cross-talk into video channels increases causing unacceptable video service degradation
Solution Approach 1:
The patent applies de-emphasis filtering to the electrical modulation signal before optical transmission to pre-shape the spectral density and reduce low-frequency components that cause Raman cross-talk. This preliminary action prevents the harmful effect from occurring in the first place, allowing full transmit power to be used without compromising video channel performance
Solution Approach 2:
The patent modifies the electrical signal parameters by applying different filtering approaches (de-emphasis, pulse shaping) to change the spectral distribution of the modulating signal. This parameter change reduces the power spectral density in frequency ranges that generate Raman cross-talk, enabling coexistence of high-power data channels and sensitive video channels
2Object-affected harmful factors
If XGPON-1 overall transmit power level is significantly reduced to mitigate Raman cross-talk impact, then video service performance is improved, but link budget and service distance requirements cannot be met
Solution Approach 1:
The patent applies local quality by selectively modifying only the low-frequency components of the electrical modulation signal through de-emphasis filtering, while maintaining full power in the data transmission. This targeted approach reduces Raman cross-talk impact on video channels without sacrificing overall transmit power or link budget performance
3Object-affected harmful factors
If pre-emphasis is applied to lower video channel modulation to mitigate Raman cross-talk, then video service performance is improved, but modifications to existing deployed PON systems and re-configuring thousands of transmitters are required
Solution Approach 1:
Instead of modifying the video transmitter (the traditional approach), the patent inverts the solution by applying de-emphasis filtering to the electrical modulation signal of the data transmitter. This approach achieves the same Raman cross-talk mitigation effect without requiring modifications to deployed video transmitters, maintaining backward compatibility and reducing deployment complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the acceptable recovery of previously degraded video channels, maintaining performance levels while reducing capital investment and installation costs, enabling the coexistence of XGPON-1 and GPON services without impacting existing deployments.
Implementation Method 1
Raman cross-talk is believed to occur from lower wavelengths into higher wavelengths. For instance, a GPON operating at 1490 nm may cause Raman cross-talk into a 1550 nm video overlay service.
Data Source
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AI summary
Disclosed are an apparatus and method configured to process video data signals operating on a passive optical network (PON). One example method of operation may include receiving a data signal at an optical distribution network node (ODN) and identifying signal interference in the data signal. The method may also include modifying a shape of the data signal in the electrical domain and transmitting the modified data signal to at least one optical termination unit (ONT).