Mode-locked thulium-holmium doped fiber laser using Bi₂Se₃ saturable absorber deposited onto arc-shaped and side-polished fibers via airbrush spraying technique

Abstract In this paper, the mode-locking performance using bismuth selenide (Bi 2 Se 3 ) as a saturable absorber in a thulium-holmium-doped fiber laser (THDFL) was demonstrated for the first time. The saturable absorber (SA) was coated using an airbrush spraying technique onto two different hosts, arc-shaped and side-polished fibers. The airbrush was used to provide an even and uniform coating onto these two hosts. The generated mode-locked pulses of the arc-shaped fiber have a center wavelength of 1913.5 nm and a 3-dB bandwidth of 3.11 nm. The optical output has a repetition frequency of 13.9 MHz and an optical pulse width of 1.33 ps. In the case of the side-polished fiber, it has a center wavelength of 1918.55 nm and a 3-dB bandwidth of 2.60 nm. The output pulse has a repetition frequency of 12.16 MHz and an optical pulse width of 1.43 ps. This demonstration indicates that the arc-shaped fiber host has a better performance in terms of shorter pulse width, which is essential for a 2 μm laser in tissue ablation procedures for medical applications.