Small but Efficient: Quasi‐1D Topological Insulator β‐Bi 4 I 4 Nanowires as a Saturable Absorber with High Modulation Depth and Broadband Operation

作者：Xiaowei Xing, Yechao Han, Xiwei Huang, Wei Chen, Zhiyang Zhang, Muwei Liu, Qingping Hu, Guojing Hu, Guoyu Xian, Qin Zhou, Xiao Lin, Haitao Yang, Hao Teng, Wenjun Liu · 发表于：Advanced Functional Materials · 年份：2025 · DOI：10.1002/adfm.202519204 · 被引用次数：9 · 研究领域：Advanced Fiber Laser Technologies、Nonlinear Photonic Systems、Photorefractive and Nonlinear Optics

Abstract As a quasi‐1D topological insulator (TI) with a unique chain‐like atomic structure and anisotropic carrier transport characteristics, β‐Bi 4 I 4 has drawn extensive interest in quantum transport, pressure‐tunable superconducting phase transitions, and advanced electronic devices. However, the broadband photon absorption capacity of β‐Bi 4 I 4 , determined by its relatively small bulk bandgap, and especially its enormous potential in the field of ultrafast optical modulation systems, remains underexplored. This work develops β‐Bi 4 I 4 as a high‐performance saturable absorber, supporting mode‐locked operation of multi‐wavelength femtosecond fiber oscillators. The device exhibits distinct nonlinear saturable absorption: it shows >60% modulation depth across three common laser operation bands and promotes the formation of a mode‐locking state for Yb‐doped, Er‐doped, and Tm‐doped fiber oscillators. This study expands broadband photonics boundaries, provides a novel design for ideal mode‐locked modulators in ultrafast fiber oscillators, and promotes the integration of TI with nonlinear optical technologies.