Passively Q-switched 1.56 μm all-fiberized laser based on evanescent field interaction with bulk-structured bismuth telluride topological insulator

We experimentally investigated the use of a bulk-structured bismuth telluride (Bi₂Te₃) topological insulator (TI) as a saturable absorption material for passive Q-switching of a fiber laser at ∼1.56 μm. Unlike previous TI-based Q-switched laser implementations that employed high-quality nanostructured TI saturable absorbers, we chose to use a bulk-structured Bi₂Te₃ TI film because it is easy to fabricate. Our saturable absorber was constructed by depositing a bulk-structured, ∼13 μm thick Bi₂Te₃ TI film, which was prepared by using a mechanical exfoliation method, on the flat side of a side-polished fiber. The modulation depth of the evanescent field interaction-based saturable absorber was measured to be ∼10.8% at ∼1.56 μm. Passively Q-switched pulses were readily obtained by incorporating the saturable absorber into an all fiberized erbium fiber-based ring cavity. The minimum temporal width was measured to be ∼2.81 μs at a repetition rate of ∼42.8 kHz. Through an output performance comparison between our Q-switched laser and recently demonstrated Q-switched fiber lasers incorporating nanostructured TI-based saturable absorbers, the pros and cons of our bulk-structured Bi₂Te₃ TI-based saturable absorbers were analyzed.