Subspace tracking for independent phase noise source separation in frequency combs

TL;DR

This paper introduces a digital signal processing method using subspace tracking and multi-heterodyne detection to identify, separate, and analyze independent phase noise sources in optical frequency combs, enhancing understanding and modeling of noise behavior.

Contribution

It presents a novel measurement technique combining subspace tracking with multi-heterodyne detection for independent phase noise source separation in optical frequency combs.

Findings

Enables separation of phase noise into multiple independent sources.

Determines how phase noise scales with comb-line number.

Provides insights into noise physics and improves noise models.

Abstract

Advanced digital signal processing techniques in combination with ultra-wideband balanced coherent detection have enabled a new generation of ultra-high speed fiber-optic communication systems, by moving most of the processing functionalities into digital domain. In this paper, we demonstrate how digital signal processing techniques, in combination with ultra-wideband balanced coherent detection can enable optical frequency comb noise characterization techniques with novel functionalities. We propose a measurement method based on subspace tracking, in combination with multi-heterodyne coherent detection, for independent phase noise sources identification, separation and measurement. Our proposed measurement technique offers several benefits. First, it enables the separation of the total phase noise associated with a particular comb-line or -lines into multiple independent phase noise terms associated with different noise sources. Second, it facilitates the determination of the scaling of each independent phase noise term with comb-line number. Our measurement technique can be used to: identify the most dominant source of phase noise; gain a better understanding of the physics behind the phase noise accumulation process; and confirm, already existing, and enable better phase noise models. In general, our measurement technique provides new insights into noise behavior of optical frequency combs.