Optical bistability of continuous-wave and multi-pulse phase transition within EDFL via low threshold saturable absorber

TL;DR

This paper reports the demonstration of optical bistability in an erbium-doped fiber laser using a low-threshold covalent organic framework saturable absorber, enabling controllable switching among laser states and revealing phase-transition-like dynamics.

Contribution

It introduces a novel low-saturation intensity COF-based saturable absorber for inducing optical bistability in EDFL, with unique transition behaviors not previously observed.

Findings

Observation of two optical bistability regions

Direct mode-locking to non-lasing transition during pump down-sweep

Presence of stable soliton-like pulses and pulse-number hysteresis

Abstract

We demonstrate optical bistability in an erbium-doped fiber laser (EDFL) using a low saturation intensity covalent organic framework (COF) saturable absorber (SA). The COF-SA satisfies the free-energy criterion for bistability, enabling switching among non-lasing, continuous-wave, and mode-locking states. Two optical bistability regions are observed, including a distinctive direct mode-locking to non-lasing transition during pump down-sweep, absent in previous EDFL studies. Stable soliton-like pulses and stepwise pulse-number hysteresis further indicate first-order phase-transition-like dynamics. These results show that low-saturation intensity SAs offer a compact route to bistability-assisted pulse formation in fiber lasers.