Joint interference of laser linewidth, chromatic dispersion, and multipath interference mitigation in self-coherent...

Area of Science:

• Optical Communications
• Signal Processing

Background:

• Self-coherent detection is key for extended-range (ER) and zero-dispersion-range (ZR) data center transmission due to its low-complexity optical field recovery.
• Laser phase noise, fiber chromatic dispersion (CD), and multipath interference (MPI) degrade performance in practical systems.
• These factors interact, causing equalization-enhanced phase noise (EEPN), phase-to-amplitude (P2A) noise, and severe system performance degradation.

Purpose of the Study:

• Investigate the combined impact of laser linewidth, fiber CD, and MPI on self-coherent optical communication systems.
• Analyze the phase noise-induced cascaded interference (PNICI) resulting from the interaction of these impairments.
• Propose a novel algorithm to mitigate PNICI and improve system performance.

Main Methods:

• Developed a joint carrier extraction-based equalization (CEE) and recursion-based maximum likelihood (R-ML) phase estimation algorithm.
• CEE mitigates MPI-induced interference via channel estimation.
• R-ML algorithm reduces PNICI phase noise with lower computational complexity than traditional ML methods.

Main Results:

• Simulations using a 56 GBaud 16-ary quadrature amplitude modulation (16-QAM) optical single-sideband (SSB) signal in a Kramers-Kronig receiver validated the CEE+R-ML scheme.
• The proposed scheme increased signal-to-interference ratio (SIR) tolerance by 5.4 dB for a 1 MHz laser linewidth after 100 km transmission.
• Achieved the 7% forward error correction (FEC) threshold at 25 dB SIR and 4 MHz laser linewidth after 100 km.

Conclusions:

• The CEE+R-ML algorithm effectively mitigates PNICI caused by the combined effects of laser linewidth, fiber CD, and MPI.
• This approach significantly enhances the performance and robustness of self-coherent optical communication systems.
• The proposed method offers a practical solution for achieving reliable high-speed data transmission over extended fiber links.