Partially decoupled polarization demultiplexing and phase noise equalizer for Alamouti code-based simplified coherent...

Area of Science:

• Optical communication systems
• Signal processing for optical communications
• Advanced modulation and coding techniques

Background:

• Alamouti space-time block code (STBC) with heterodyne coherent receivers offers cost-effective polarization-insensitive phase-diversity detection.
• Existing joint equalizers for STBC require complex, multi-parameter updates, leading to slow convergence and limited phase noise tolerance.

Purpose of the Study:

• To propose and evaluate a novel partially decoupled equalizer to accelerate convergence and improve phase noise tolerance in STBC receivers.
• To reduce the complexity of polarization demultiplexing and phase tracking in optical communication systems.

Main Methods:

• A polarization and phase decoupled equalizer (PPDE) utilizing a single step-size parameter for polarization demultiplexing.
• A pilot-aided blind phase search (P-BPS) algorithm for carrier phase recovery, enhancing phase noise tolerance and addressing cyclic slip.
• Numerical simulations and experimental validation using quadrature phase-shift keying (QPSK) signals.

Main Results:

• The proposed PPDE requires approximately half the number of iterations for convergence compared to the conventional joint equalizer.
• The system maintains polarization-insensitive characteristics even under significant phase noise conditions.
• The P-BPS algorithm demonstrates a threefold increase in achievable linewidth tolerance compared to the DD-LMS algorithm.

Conclusions:

• The partially decoupled equalizer significantly improves convergence speed and reduces complexity in STBC systems.
• The P-BPS algorithm offers superior phase noise and linewidth tolerance, crucial for robust optical communication.
• The proposed approach provides a more efficient and tolerant solution for cost-effective polarization-insensitive detection in optical systems.