Phase Noise Characterization of Cr:ZnS Frequency Comb using Subspace Tracking

TL;DR

This paper characterizes the phase noise of a mid-IR Cr:ZnS frequency comb using a novel measurement technique, revealing dominance of common mode noise and negligible high-order noise contributions.

Contribution

It introduces a subspace tracking-based phase noise measurement method for Cr:ZnS frequency combs, enabling detailed noise analysis with a single setup.

Findings

Common mode phase noise dominates the comb's noise profile.

High-order phase noise terms are below the measurement noise floor.

The measurement technique effectively isolates different phase noise components.

Abstract

We present a comprehensive phase noise characterization of a mid-IR Cr:ZnS frequency comb. Despite their emergence as a platform for high-resolution dual-comb spectroscopy, detailed investigations into the phase noise of Cr:ZnS combs have been lacking. To address this, we use a recently proposed phase noise measurement technique that employs multi-heterodyne detection and subspace tracking. This allows for the measurement of the common mode, repetition-rate and high-order phase noise terms, and their corresponding scaling as a function of a comb-line number, using a single measurement set-up. We demonstrate that the comb under test is dominated by the common mode phase noise, while all the other phase noise terms are below the measurement noise floor (~ -120 dB rad^2/Hz), and are thereby not identifiable.