Lead‐Free EtbtBi₂I₁₀ Nanocrystals: a Promising Saturable Absorber for Ultrafast Photonics

Abstract EtbtBi 2 I 10 , a promising lead‐free perovskite crystal, has garnered attention in photocatalysis due to its high stability, low toxicity, and broad absorption spectrum. However, its application in ultrafast optical devices remains unexplored. Herein, the synthesis of EtbtBi 2 I 10 nanocrystals and the characterization of their nonlinear saturable absorption properties are reported. Utilizing these properties, a saturable absorber is fabricated that enables stable mode‐locked in erbium‐doped fiber lasers. The results revealed a fundamental mode‐locked pulse width of 671.43 fs, with harmonic mode‐locked achieved at a repetition rate of 558.9 MHz (corresponding to the 115th harmonic). Additionally, stable bound‐state soliton mode‐locked is observed. These findings establish EtbtBi 2 I 10 as an outstanding nonlinear optical material, offering substantial potential for ultrafast photonic applications.