Passively Q-switched 156  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 (Bi sub(2)Te sub(3)) topological insulator (TI) as a saturable absorption material for passive Q-switching of a fiber laser at ~ 1.56 mu m. Unlike previous TI-based Q-switched laser implementations that employed high-quality nanostructured TI saturable absorbers, we chose to use a bulk-structured Bi sub(2) Te sub(3) TI film because it is easy to fabricate. Our saturable absorber was constructed by depositing a bulk-structured, ~ 13 mu m thick Bi sub(2) Te sub(3) 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 mu m. 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 mu s 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 Bi sub(2) Te sub(3) TI-based saturable absorbers were analyzed.