研究目的
To experimentally characterize the statistical behaviors of bit-wise achievable information rates and effective signal-to-noise ratios due to polarization dependent loss for probabilistically shaped and uniform dual-polarization 64-QAM.
研究成果
The experimental results demonstrate that distributed link PDL causes BW AIR and effective SNR to follow shifted mirror-image Maxwell PDFs. Probabilistic shaping reduces outage probability significantly (e.g., by a factor of 400 for 1.3 dB per-loop PDL at 1200 km) compared to uniform constellations, but the transmission distance increase due to shaping is reduced by 50% for an outage probability threshold. An optimized shaping PMF considering SNR fluctuations from PDL could potentially improve performance further.
研究不足
The experimental setup uses a single-span loop which may not fully represent multi-span systems; intrinsic PDL of loop components is non-negligible. Standard QAM receiver DSP might be less efficient for shaped constellations under high PDL. The study is limited to specific PDL values and transmission distances; generalizability to other conditions may require further investigation. Automation and number of measurements (1000 per case) ensure accuracy but could be resource-intensive.
1：Experimental Design and Method Selection:
A single-span recirculating loop setup is used to emulate distributed link PDL. The experiment involves transmitting DP 64-QAM signals at 250 Gb/s, with offline signal processing to compute BW AIR and effective SNR. The methodology includes using a polarization controller and PDL emulator to simulate PDL effects, and automated measurements with 1000 realizations for statistical accuracy.
2：Sample Selection and Data Sources:
Two uncorrelated 2^17 pseudo-random symbol sequences are generated for shaped and uniform constellations. Data is captured using a coherent receiver after transmission through the loop.
3：List of Experimental Equipment and Materials:
Arbitrary waveform generator (AWG), IQ modulators, EDFAs, optical bandpass filters (OBPFs), polarization controller (PolCon), PDL emulator (PDLE), acousto-optic modulator (AOM), variable optical attenuator (VOA), coherent receiver, and single-mode fiber spans.
4：Experimental Procedures and Operational Workflow:
Digital waveforms are generated and uploaded to the AWG, modulated optically, and launched into the recirculating loop. The loop includes a fiber span, EDFA, OBPF, PolCon, PDLE, and other components. The PolCon uses random rotation matrices to vary the state of polarization. Signals are received, digitized, and processed offline using DSP algorithms including matched filtering, dispersion compensation, equalization, and carrier phase estimation.
5：Data Analysis Methods:
BW AIR and effective SNR are calculated using Monte Carlo integration and formulas based on non-circularly symmetric bivariate Gaussian PDF assumptions. Histograms are fitted to shifted mirror-image Maxwell PDFs, and outage probabilities are derived from cumulative distribution functions.
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