A femtosecond pulse erbium fiber laser incorporating a saturable absorber based on bulk-structured Bi₂Te₃ topological insulator

We experimentally demonstrate the use of a bulk-structured Bi ₂Te₃ topological insulator (TI) as an ultrafast mode-locker to generate femtosecond pulses from an all-fiberized cavity. Using a saturable absorber based on a mechanically exfoliated layer about 15 μm thick deposited onto a side-polished fiber, we show that stable soliton pulses with a temporal width of ∼600 fs can readily be produced at 1547 nm from an erbium fiber ring cavity. Unlike previous TI-based mode-locked laser demonstrations, in which high-quality nanosheet-based TIs were used for saturable absorption, we chose to use a bulk-structured Bi₂Te ₃ layer because it is easy to fabricate. We found that the bulk-structured Bi₂Te₃ layer can readily provide sufficient nonlinear saturable absorption for femtosecond modelocking even if its modulation depth of ∼15.7% is much lower than previously demonstrated nanosheet-structured TI-based saturable absorbers. This experimental demonstration indicates that high-crystalline-quality atomic-layered films of TI, which demand complicated and expensive material processing facilities, are not essential for ultrafast laser modelocking applications.