Passively Q-Switched 1.89-μm Fiber Laser Using a Bulk-Structured Bi₂Te₃ Topological Insulator

We experimentally demonstrate that a bulk-structured Bi₂Te₃ topological insulator (TI) film deposited on a side-polished fiber can act as an effective Q-switch for a 1.89-μm laser. Our bulk-structured Bi₂Te₃ TI film with a thickness of ∼31 μm, was prepared using a mechanical exfoliation method, and the fabricated film was transferred onto a side-polished SM2000 fiber to form a fiberized saturable absorber based on evanescent field interaction. By incorporating the saturable absorber into a thulium (Tm)-holmium (Ho) co-doped fiber-based ring cavity, it is shown that Q-switched pulses with a minimum temporal width of ∼1.71 μs can readily be produced at a wavelength of 1.89 μm. The output pulse repetition rate was tunable from ∼35 to ∼60 kHz depending on the pump power. The maximum output pulse energy was ∼11.54 nJ at a pump power of 250 mW. The output performance of our laser is compared to that of the 1.98-μm Q-switched fiber laser based on a nanosheet-based Bi₂Se₃ TI demonstrated previously by Luo et al.