Ultra-Broadband Coherent Supercontinuum Frequency Comb

TL;DR

This paper investigates the coherence properties of an ultra-broadband supercontinuum frequency comb, demonstrating its potential for high-precision laser comparisons and revealing quantum noise effects and fiber gain influences.

Contribution

It introduces a new method using continuous wave lasers to analyze supercontinuum coherence across the spectrum and provides the first numerical simulation of accumulated comb coherence over many pulses.

Findings

Supports Hz-level comparison of ultrastable lasers at multiple wavelengths

Reveals quantum-seeded broadband amplitude noise without phase coherence loss

Discovers dependence of super-continuum coherence on fiber fractional Raman gain

Abstract

We present detailed studies of the coherence properties of an ultra-broadband super-continuum, enabled by a new approach involving continuous wave laser sources to independently probe both the amplitude and phase noise quadratures across the entire spectrum. The continuum coherently spans more than 1.5 octaves, supporting Hz-level comparison of ultrastable lasers at 698 nm and 1.54 {\mu}m. We present the first numerical simulation of the accumulated comb coherence in the limit of many pulses, in contrast to the single-pulse level, with systematic experimental verification. The experiment and numerical simulations reveal the presence of quantum-seeded broadband amplitude noise without phase coherence degradation, including the discovery of a dependence of the super-continuum coherence on the fiber fractional Raman gain.