Semiconducting Polymer Dots as Saturable Absorbers for Mode-Locked Thulium-Doped Fiber Lasers

We demonstrated an all-fiber passively mode-locked thulium-doped fiber laser (TDFL) using organic semiconducting polymer dots (Pdots) based saturable absorber (SA). The Pdots are prepared by methods of donor-acceptor moieties and reprecipitation, which possess a broadband absorption from 400 to 2200 nm and nonlinear saturable absorption property at 2 mu m . By depositing the Pdots onto the microfiber as an SA, long nonlinear interaction length of evanescent wave and Pots can be achieved. An ultrafast fiber laser operating at 1926 nm was observed. The output power could reach to 76.2 mW at the maximum pump power of 2.1 W. Compared with Pdot-film SAs in our previous work, these experimental results verify that Pdot-SAs functioned with evanescent field interaction are promising nonlinear optical modulators for ultrafast and high-power pulse generation.