On achievable rates for long-haul fiber-optic communications

Area of Science:

• Optical Communications Engineering
• Information Theory
• Digital Signal Processing

Background:

• Mutual Information (MI) is a key metric for optical communication system performance.
• Traditional metrics like Q-factor have limitations in accurately predicting system rates.
• Understanding MI's behavior is crucial for advancing long-haul fiber systems.

Purpose of the Study:

• To derive and present practical expressions for calculating lower bounds on MI in optical fiber systems.
• To investigate the impact of various system parameters on achievable transmission rates.
• To advocate for the use of MI over Q-factor for performance evaluation.

Main Methods:

• Derivation of ready-to-use expressions for MI lower bounds.
• Extensive numerical simulations of long-haul optical fiber systems.
• Analysis of system components including transmitter, receiver, and channel characteristics.

Main Results:

• Quantification of how modulation formats (e.g., quadrature amplitude modulation), channel spacing, digital back-propagation, and probabilistic shaping influence MI.
• Demonstration of practical MI calculation methods.
• Identification of MI as a superior metric compared to Q-factor for coded optical systems.

Conclusions:

• The presented MI calculation methods provide valuable tools for system design and optimization.
• MI offers a more comprehensive understanding of achievable transmission rates than Q-factor.
• Optimizing system parameters through MI analysis can significantly enhance long-haul optical communication performance.