Polarization‐Selective Switchable Mode‐Locked Pulses in Fiber Lasers Based on Anisotropic Quasi‐2D Perovskites

Multi‐state switchable pulsed lasers are crucial components in advanced ultrafast photonic systems. Low‐dimensional materials with superior anisotropy and nonlinear optical properties exhibit polarization‐dependent tunability, enabling switchable laser modulation. In this study, a quasi‐2D Ruddlesden‐Popper phase perovskite have successfully synthesized, denoted as (PEA) 2 (MA) n‐1 Pb n Br 3n+1 (PMPB). Polarization‐resolved measurements have revealed significant anisotropic properties associated with PMPB, including photoluminescence, second‐ and third‐order nonlinear optical behavior, and carrier relaxation dynamics. First‐principles calculations have established the underlying physical mechanisms. The PMPB nonlinear absorption properties exhibit variations under laser excitation in different polarization directions, facilitating ultrafast laser modulation. Operation of a fiber laser system based on the PMPB saturable absorber resulted in an observed soliton evolution from the conventional form to high‐order harmonic mode‐locking and dark‐bright soliton pairs to giant pulse mode‐locking. In addition, a stable and reversible switching between bright soliton harmonic mode‐locking and giant pulse mode‐locking based on the PMPB polarization‐dependent nonlinear optical properties is achieved. Numerical simulations have validated the experimental results and demonstrated a practical application using the two switchable laser output states. The findings of this study establish the significant potential of PMPB as an anisotropic nonlinear optical material for use in advanced multi‐state switchable pulsed lasers.