Unveiling the temporal dynamics in multi-longitudinal mode ytterbium-doped fiber lasers

TL;DR

This paper introduces a comprehensive spatio-temporal model for ytterbium-doped fiber lasers, revealing dual time scale dynamics and various instabilities, advancing understanding of their temporal behavior across different regimes.

Contribution

It presents a novel unified model capable of capturing the full temporal evolution of multi-longitudinal mode YDFLs from nanoseconds to milliseconds, highlighting dual time scale characteristics and instability mechanisms.

Findings

Identification of dual time scale features in YDFL dynamics

Simulation of three types of temporal instabilities

Clarification of the role of mode superposition in instabilities

Abstract

In this work, we propose a unified spatio-temporal model to study the temporal dynamics in continuously pumped ytterbium-doped fiber lasers (YDFLs). Different from previously reported theories, this model is capable of obtaining the temporal evolution of an YDFL from relaxation oscillation region to relative stable region in different time scales ranging from sub-nanosecond to millisecond. It reveals that there exists dual time scale characteristics in the temporal evolution of a multi-longitudinal mode YDFL. Specifically, the temporal evolution would experience sharp change during one cavity round-trip while keep relatively stable between adjacent cavity round-trips. Representative cases are simulated to study the influences of structure parameters on the temporal dynamics and the longitudinal mode characteristics in YDFLs. Three types of temporal instabilities, i.e. sustained self-pulsing, self-mode locking, and turbulence-like pulsing, coexist in a multi-longitudinal mode YDFL. The simulation results clarify that the three temporal instabilities are all the reflectors of intrinsic characteristics of longitudinal modes superposition in multi-longitudinal mode YDFLs. In addition, the strength of the irregular sustained self-pulsing is the major issue which impacts the macroscopic temporal fluctuations in YDFLs.