Zero-overhead phase noise compensation via decision-directed phase equalizer for coherent optical OFDM

Area of Science:

• Optical Communications
• Signal Processing
• Photonics

Background:

• Long-haul coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems face challenges from laser phase noise.
• Existing compensation methods can introduce overhead, impacting system efficiency.
• Accurate phase noise estimation and compensation are crucial for maintaining signal integrity over extended distances.

Purpose of the Study:

• To investigate the feasibility of a zero-overhead laser phase noise compensation (PNC) technique.
• To evaluate the performance of the decision-directed phase equalizer (DDPE) in CO-OFDM systems.
• To analyze the impact of fiber nonlinearity and amplified spontaneous emission (ASE) noise on the DDPE performance.

Main Methods:

• Implemented and numerically simulated a decision-directed phase equalizer (DDPE) for CO-OFDM systems.
• DDPE estimates phase noise by averaging phase drift across OFDM sub-channels after initial symbol decisions.
• Compared DDPE performance against the conventional equalizer (CE) for various laser linewidths over 2000 km of single-mode fiber (SMF) at 40 Gb/s.

Main Results:

• DDPE achieves zero-overhead phase noise compensation in long-haul CO-OFDM transmission.
• The method effectively mitigates phase noise, outperforming the conventional equalizer for different laser linewidths.
• Analysis shows DDPE's complexity is comparable to CE, with fewer complex multiplications per bit.

Conclusions:

• Zero-overhead PNC using DDPE is feasible and effective for long-haul CO-OFDM systems.
• DDPE offers a promising solution for enhancing signal quality and spectral efficiency in optical networks.
• The method demonstrates robustness against fiber nonlinearity and ASE noise.