# From instable directional switching to controlled unidirectional operation in a nonlinear fiber ring laser

## TL;DR

The paper explores how a fiber ring laser can switch from unstable bidirectional to stable unidirectional operation with increased pump power.

## Contribution

The study introduces a simplified experimental setup that enables the identification of specific nonlinear effects in fiber lasers.

## Key findings

- A fiber ring laser switches to unidirectional operation above a certain pump power threshold.
- Stimulated Raman scattering is identified as a key factor in triggering unidirectional operation.
- The pump power threshold for unidirectional operation was reduced from 30 to 3.8 W.

## Abstract

We investigate a new phenomenon, where a reciprocal fiber ring laser switches from bidirectional to unidirectional operation above a certain pump power threshold. Significant simplifications regarding earlier experiments are presented, which for the first time allow the identification of individual nonlinear effects. We highlight the unique role of stimulated Raman scattering in triggering unidirectional operation, and that additional conditions apply. The threshold is reduced from 30 to 3.8 W, which eases potential applications.