Tea polyphenol polymer film enables broadband optical modulation for hybrid mode-locked ultrafast fiber lasers

Materials exhibiting broadband nonlinear optical responses are critically important for ultrafast photonics applications, particularly as saturable absorbers (SAs) that facilitate broadband optical pulse generation. In this study, tea polyphenol-polyvinyl alcohol (TP-PVA) composite films are synthesized via a polymer embedding method and employed as SAs to initiate ultrafast pulse operation in fiber lasers. The TP-PVA SA film exhibits excellent broadband saturable absorption performance at wavelengths of 1.0 μm, 1.5 μm, and 2.0 μm, with modulation depths of 54.21%, 41.41%, and 51.16%, respectively. Stable passively mode-locked pulses with pulse widths of 588 fs, 419 fs, and 743 fs are generated in Yb-, Er-, and Tm-doped fiber lasers, respectively. This work confirms the effective performance of TP-PVA as a broadband SA, and establishes a foundation for the integration of novel and sustainable materials within ultrafast photonic systems. The approach paves the way for developing compact broadband ultrafast laser systems operating in the near-infrared spectral region.