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Pump RIN-induced impairments in unrepeatered transmission systems using distributed Raman amplifier
Optics Express
|May 14, 2015
Summary
Pump relative intensity noise (RIN) in distributed Raman amplifiers (DRAs) causes distortions in high spectral efficiency signals. PM-16QAM signals are more sensitive than PM-QPSK, especially with higher-order DRAs, but digital signal processing can mitigate these impairments.
Area of Science:
- Optical Communications
- Signal Processing
Background:
- Unrepeatered transmission systems using distributed Raman amplifiers (DRAs) are crucial for high spectral efficiency.
- Accurate DRA design is essential for optimizing performance and mitigating impairments like pump relative intensity noise (RIN).
- Pump RIN can induce signal distortions, including intensity noise, phase noise, and polarization crosstalk.
Purpose of the Study:
- To analyze pump RIN-induced distortions on high spectral efficiency modulation formats in unrepeatered systems.
- To investigate the impact of RIN on polarization-multiplexed Quadrature Phase Shift Keying (PM-QPSK) and 16-Quadrature Amplitude Modulation (PM-16QAM) signals.
- To evaluate the effectiveness of digital signal processing (DSP) algorithms in mitigating these impairments.
Main Methods:
- Utilized vector theory and Jones-matrix formalism to describe stimulated Raman scattering (SRS) effects.
- Derived an analytical model for relative phase noise (RPN) in higher-order DRAs.
- Performed simulations of PM-QPSK and PM-16QAM systems using 1st, 2nd, and 3rd-order forward-pumped Raman amplifiers.
Main Results:
- PM-QPSK signals experience negligible impairments in 1st and 2nd-order DRAs at realistic RIN levels, but significant degradation in 3rd-order DRAs.
- PM-16QAM signals show greater sensitivity, with 2nd and 3rd-order DRAs causing non-negligible performance degradations.
- The study analyzed the impact of RIN-induced impairments including SRS, cross-phase modulation (XPM), and cross-polarization modulation (XPolM).
Conclusions:
- Higher-order DRAs are more susceptible to pump RIN-induced impairments, particularly affecting advanced modulation formats like PM-16QAM.
- The choice of DRA order and modulation format significantly impacts system performance under realistic RIN conditions.
- DSP algorithms show potential for mitigating RIN-induced impairments, offering a pathway for enhanced system resilience.
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