Mechanically exfoliated black phosphorus as a new saturable absorber for both Q-switching and Mode-locking laser operation

TLDR

Black phosphorus is a narrow band‑gap 2D material that shows saturable absorption under strong illumination, bridging graphene and transition‑metal dichalcogenides. The study aims to fabricate mechanically exfoliated BP saturable absorbers and demonstrate their use in ultrafast laser photonics. The BP saturable absorbers were characterized using a balanced synchronous twin‑detector method at telecom wavelengths. In Erbium‑doped fiber lasers, the BP SA enabled passive Q‑switching with 94.3 nJ pulses and mode‑locking down to 946 fs, demonstrating its suitability for pulsed fiber and solid‑state lasers.

Abstract

Black phosphorus (BP), an emerging narrow direct band-gap two-dimensional (2D) layered material that can fill the gap between the semi-metallic graphene and the wide-bandgap transition metal dichalcogenides (TMDs), had been experimentally found to exhibit the saturation of optical absorption if under strong light illumination. By taking advantage of this saturable absorption property, we could fabricate a new type of optical saturable absorber (SA) based on mechanically exfoliated BPs, and further demonstrate the applications for ultra-fast laser photonics. Based on the balanced synchronous twin-detector measurement method, we have characterized the saturable absorption property of the fabricated BP-SAs at the telecommunication band. By incorporating the BP-based SAs device into the all-fiber Erbium-doped fiber laser cavities, we are able to obtain either the passive Q-switching (with maximum pulse energy of 94.3 nJ) or the passive mode-locking operation (with pulse duration down to 946 fs). Our results show that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.