Broadband nonlinear optical response in multi-layer black phosphorus: an emerging infrared and mid-infrared optical material

TLDR

Black phosphorus is a high‑mobility layered semiconductor with a tunable direct band‑gap from 0.3 to 2.0 eV, strong light‑matter interaction, and a broad, adjustable optical response that makes it a promising nonlinear material for infrared and mid‑infrared applications. We experimentally demonstrated that ~10 nm multilayer black phosphorus exhibits broadband saturable absorption from 400 nm to at least 1930 nm, indicating its potential as a two‑dimensional saturable absorber for ultrafast photonic devices such as Q‑switchers, mode‑lockers, and optical switches.

Abstract

Black phosphorous (BP), the most thermodynamically stable allotrope of phosphorus, is a high-mobility layered semiconductor with direct band-gap determined by the number of layers from 0.3 eV (bulk) to 2.0 eV (single layer). Therefore, BP is considered as a natural candidate for broadband optical applications, particularly in the infrared (IR) and mid-IR part of the spectrum. The strong light-matter interaction, narrow direct band-gap, and wide range of tunable optical response make BP as a promising nonlinear optical material, particularly with great potentials for infrared and mid-infrared opto-electronics. Herein, we experimentally verified its broadband and enhanced saturable absorption of multi-layer BP (with a thickness of ~10 nm) by wide-band Z-scan measurement technique, and anticipated that multi-layer BPs could be developed as another new type of two-dimensional saturable absorber with operation bandwidth ranging from the visible (400 nm) towards mid-IR (at least 1930 nm). Our results might suggest that ultra-thin multi-layer BP films could be potentially developed as broadband ultra-fast photonics devices, such as passive Q-switcher, mode-locker, optical switcher etc.