Unveiling the relative timing jitter in counter propagating all normal dispersion (CANDi) dual-comb fiber laser

TL;DR

This paper introduces a novel, reference-free method to measure the relative timing jitter in CANDi dual-comb fiber lasers with femtosecond precision, revealing pump RIN as the main jitter source and guiding performance improvements.

Contribution

It enhances CANDi laser pulse energy, develops a new RTJ measurement technique, and identifies pump RIN as the primary factor affecting RTJ, providing insights for performance optimization.

Findings

Pulse energy increased from 1 nJ to 8 nJ.

RTJ measurement precision of 1.8 fs achieved.

Pump RIN identified as main RTJ contributor.

Abstract

Counter-propagating all-normal dispersion (CANDi) fiber laser is an emerging high-energy single-cavity dual-comb laser source. Its relative timing jitter (RTJ), a critical parameter for dual-comb timing precision and spectral resolution, has not been comprehensively investigated. In this paper, we enhance the state-of-the-art CANDi fiber laser pulse energy from 1 nJ to 8 nJ. We then introduce a novel reference-free RTJ characterization technique that provides shot-to-shot measurement capability at femtosecond precision for the first time. The measurement noise floor reaches 1.6x10-7 fs2/Hz, and the corresponding integrated measurement precision is only 1.8 fs (1 kHz, 20 MHz). With this new characterization tool, we are able to study the physical origin of CANDi laser's RTJ in detail. We first verify that the cavity length fluctuation does not contribute to the RTJ. Then we measure the integrated RTJ to be 39 fs (1 kHz, 20 MHz) and identify the pump relative intensity noise (RIN) to be the dominant factor responsible for it. In particular, pump RIN is coupled to the RTJ through the Gordon-Haus effect. Finally, solutions to reduce the free-running CANDi laser's RTJ are discussed. This work provides a general guideline to improve the performance of compact single-cavity dual-comb systems like CANDi laser benefitting various dual-comb applications.