  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.
