Laser Frequency Noise in Coherent Optical Systems: Spectral Regimes and Impairments

Area of Science:

• Optical Communications
• Signal Processing
• Photonics

Background:

• Coherent communication networks utilize multi-dimensional lightwave properties and electrical-domain dispersion compensation (EDC).
• EDC enhances network flexibility and nonlinearity tolerance but increases susceptibility to laser frequency noise (FN).
• Existing studies primarily analyze white FN, leaving the impact of realistic non-white FN spectra largely unaddressed.

Purpose of the Study:

• To develop and experimentally validate a theory for coherent optical links with non-white laser FN and EDC.
• To elucidate the fundamental mechanisms linking non-white FN to system impairments.
• To provide design criteria for mitigating FN-induced issues in optical communication systems.

Main Methods:

• Development of a theoretical framework for analyzing non-white laser FN spectra in coherent links with EDC.
• Experimental validation of the developed theory.
• Analysis of FN-induced symbol displacement, timing jitter, and inter/intra-symbol interference.

Main Results:

• Non-white FN spectra cause FN-induced symbol displacement, leading to timing jitter and inter/intra-symbol interference.
• Different FN spectral regimes induce distinct types of impairments.
• Some impairments are mitigable through algorithm optimization, while others result in irretrievable signal degradation.

Conclusions:

• A comprehensive theory for non-white FN in coherent optical links with EDC has been established and experimentally validated.
• Understanding the specific FN spectral regimes is critical for designing effective mitigation strategies.
• Theoretical boundaries and design criteria are provided for optimizing system and laser parameters to manage FN-induced impairments.