Semiconducting Polymer Dots as Broadband Saturable Absorbers for Q-switched Fiber Lasers

Semiconducting polymer dots (Pdots) have attracted much attention due to their outstanding optical properties. However, the potential of Pdots in laser technology is rarely studied. Here, we first report the benzobisthiadiazole (BBT)-based Pdot as a single broadband nonlinear saturable absorber (SA) for passively Q-switched fiber lasers at 1, 1.5, and 2 μm. The Pdot-SA possesses a strong saturable absorption, a broadband nonlinear optical response, and a large modulation depth. Once the Pdot-SA is integrated into the ytterbium-, erbium-, and thulium-doped fiber laser cavities, stable Q-switched operations are observed at the central wavelengths of 1036, 1561, and 1951 nm. Our results verify that the Pdots are promising nonlinear media for Q-switched pulse generation, and highlight the potential of Pdots for relevant nonlinear optical applications.