# Coherent perfect absorption in a weakly absorbing fiber

## TL;DR

This paper demonstrates a method to achieve complete absorption in a weakly absorbing short-length Er-doped fiber using coherent perfect absorption with fiber Bragg gratings, enabling efficient fiber lasers.

## Contribution

It introduces a novel approach employing fiber Bragg gratings to realize coherent perfect absorption in weakly absorbing fibers, independent of intrinsic absorption.

## Key findings

- Achieved complete absorption in weakly absorbing fibers
- Enabled potential for single-longitudinal-mode fiber lasers
- Applicable across various spectral windows

## Abstract

Short-length fiber lasers are key elements for device integration in fiber systems. However, efficiently absorbing a pump beam in a short ion-doped fiber remains a challenge. We present an approach that renders a weakly absorbing short-length Er-doped fiber completely absorbing. We exploit the concept of coherent perfect absorption, whereby two appropriately designed fiber Bragg gratings define a short-length cavity that enforces complete absorption of an incident wave on resonance independently of the fiber intrinsic absorption. This approach applies to any spectral window and may lead to efficient single-longitudinal-mode fiber lasers for applications in optical communication, sensing, and metrology.