Impairment mitigation in superchannels with digital backpropagation and MLSD

Area of Science:

• Optical Communications
• Digital Signal Processing
• High-Speed Networks

Background:

• Superchannel transmission is crucial for increasing data rates in optical networks.
• Dispersion uncompensated links pose significant challenges for signal integrity.
• Spectral shaping techniques are employed to manage carrier spacing and inter-channel interference.

Purpose of the Study:

• To numerically assess the performance of SC-DBP and MLSD algorithms in DP-QPSK and DP-16QAM superchannels.
• To investigate the impact of different spectral shaping methods (RZ, NRZ optical pre-filtering, digital Nyquist filtering) on algorithm performance.
• To determine the optimal carrier proximity limits for each spectral shaping technique and modulation format.

Main Methods:

• Numerical simulations of superchannel transmission over dispersion uncompensated links.
• Evaluation of single-carrier digital backpropagation (SC-DBP) and maximum-likelihood sequence detection (MLSD).
• Comparison of performance across three spectral shaping techniques: RZ optical pre-filtering, NRZ optical pre-filtering, and digital Nyquist filtering.

Main Results:

• Both SC-DBP and MLSD algorithms provide performance improvements, up to 1.0 dB in Q(2)-factor, especially when carrier spacing approaches the Nyquist limit.
• The effectiveness of these algorithms is dependent on the spectral shaping technique employed.
• Performance gains are significantly reduced for higher-order modulation formats such as DP-16QAM compared to DP-QPSK.

Conclusions:

• SC-DBP and MLSD are effective in mitigating impairments in closely spaced superchannels.
• The choice of spectral shaping method critically influences the achievable performance gains.
• Future research should focus on optimizing these algorithms for advanced modulation formats to maximize spectral efficiency.