# Optimized Er/Yb fiber laser

## TL;DR

This paper experimentally optimizes the output coupler reflectivity of an Er/Yb fiber laser, achieving high efficiency and demonstrating in-situ inscription of the coupler during laser operation.

## Contribution

It provides the first experimental determination of the optimal output coupler reflectivity for Er/Yb fiber lasers and introduces in-situ inscribing techniques during laser operation.

## Key findings

- Optimal reflectivity is approximately 1%.
- Laser efficiency reaches about 38% with optimal coupler.
- In-situ inscribed couplers yield comparable output power.

## Abstract

We measure the output power of an Er/Yb fiber laser with twelve different SMF-28 narrowband output couplers and demonstrate experimentally that the optimal reflectivity is ~ 1 %. The fiber laser efficiency with the optimal output coupler is ~ 38 %. In addition, we successfully inscribe a similar output coupler in-situ during laser operation with 800 nm femtosecond pulses and the phase mask technique. An output power very close to the optimal was obtained with the in-situ inscribed output coupler.