High‐repetition‐rate ultrafast fiber lasers enabled by BtzBiI ₄ : a novel bismuth‐based perovskite nonlinear optical material

Recent advances in perovskite crystals have highlighted their exceptional optical properties, making them promising candidates for a wide range of photonic applications. However, the exploration of high-repetition-rate laser systems based on these materials remains underdeveloped, hindering their potential in ultrafast laser technologies and related fields such as optical communications and precision metrology. In this study, we present, for the first time, the saturable absorption characteristics of a novel organic-inorganic hybrid perovskite incorporating the heavy metal bismuth (Bi), specifically N-methylbenzothiazoleBiI₄ (BtzBiI₄). The material was integrated as a saturable absorber (SA) into a passively mode-locking erbium-doped fiber laser. By harnessing the exceptional optical nonlinearity of BtzBiI₄-SA, we successfully achieved stable fundamental mode-locking, harmonic mode-locking, and bound-state soliton mode-locking within a single cavity. The fundamental mode-locking yielded pulses with a duration of 844 fs and a signal-to-noise ratio of 66.15 dB. Additionally, the 142nd-order harmonic solitons attained an impressive repetition rate of 1.3202 GHz. These results represent a significant step forward in the realization of high-repetition-rate fiber lasers utilizing perovskite materials. Our findings highlight the remarkable potential of BtzBiI₄ as a high-performance nonlinear optical material, paving the way for next-generation ultrafast photonic devices.