研究目的
Investigating the laser phase noise tolerance of probabilistically shaped (PS) and uniformly shaped (US) quadrature amplitude modulation (QAM) signals for high spectral efficiency systems.
研究成果
The study concludes that PS signals can achieve higher performance with narrow linewidth lasers or high pilot ratios, but their performance degrades with large phase noise and high-order modulation formats. The choice between PS and US signals depends on the laser linewidth and carrier phase recovery algorithm used.
研究不足
The study is limited to specific QAM formats and laser linewidths. The impact of phase noise on higher order QAM formats and the trade-off between pilot ratio and achievable information rate are highlighted as areas for further optimization.
1：Experimental Design and Method Selection:
The study employs numerical simulations and experimental evaluations to compare the phase noise tolerance of PS and US QAM signals under the same information rate. A pilot-assisted digital phase locked loop is used for carrier phase recovery.
2：Sample Selection and Data Sources:
The experiments use PDM 16-GBd PS-1024QAM and US-256QAM signals with lasers of 0.1-kHz and 40-kHz linewidths.
3：1-kHz and 40-kHz linewidths. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes micro-integrable tunable laser assemblies (μITLAs), distributed feedback (DFB) fiber lasers, arbitrary waveform generator (AWG), PDM-IQ modulator (PDM-IQM), erbium-doped fiber amplifier (EDFA), optical bandpass filter (OBPF), coherent receiver with 90° hybrid and balanced photo detectors (BPDs), and a digital sampling oscilloscope (DSO).
4：Experimental Procedures and Operational Workflow:
Signals are generated, modulated, amplified, filtered, and then received and digitized for analysis. The phase noise is compensated using a pilot-assisted digital PLL, and performance metrics are calculated.
5：Data Analysis Methods:
The performance is evaluated based on the required optical signal-to-noise ratio (OSNR) at the forward error correction limit and the achievable information rate (AIR).
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micro-integrable tunable laser assemblies
μITLAs
NTT
Used as a laser source with a 40-kHz linewidth for evaluating phase noise tolerance.
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distributed feedback fiber laser
DFB
NTT
Used as a laser source with a 0.1-kHz linewidth for evaluating phase noise tolerance.
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arbitrary waveform generator
AWG
Used to emit electrical signals for modulation.
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PDM-IQ modulator
PDM-IQM
Used to modulate the signals.
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erbium-doped fiber amplifier
EDFA
Used to amplify the signals.
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optical bandpass filter
OBPF
Used to filter the signals.
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coherent receiver
Used to convert optical signals to electrical ones.
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digital sampling oscilloscope
DSO
Used to digitize the signals.
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