Passively Q-Switched 1.89- mu m Fiber Laser Using a Bulk-Structured Bi sub(2)Te sub(3) Topological Insulator

We experimentally demonstrate that a bulk-structured Bi sub(2)Te sub(3) topological insulator (TI) film deposited on a side-polished fiber can act as an effective Q-switch for a 1.89- mu m laser. Our bulk-structured Bi sub( 2)Te sub(3) TI film with a thickness of similar to 31 mu m, 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 similar to 1.71 mu s can readily be produced at a wavelength of 1.89 mu m. The output pulse repetition rate was tunable from similar to 35 to similar to 60 kHz depending on the pump power. The maximum output pulse energy was similar to 11.54 nJ at a pump power of 250 mW. The output performance of our laser is compared to that of the 1.98- mu m Q-switched fiber laser based on a nanosheet-based Bi sub(2)Se sub(3) TI demonstrated previously by Luo et al.