3 GHz passively harmonic mode-locked Er-doped fiber laser by evanescent field-based nano-sheets topological insulator

In this paper, we report on the experimental observation of harmonic mode locking (HML) fiber laser based on evanescent field of tapered fiber using topological insulator (TI) Bi2Te3 saturable absorber (SA). The optical deposition method was adopted to fabricate the tapered fiber-based TISA. By significant nonlinear optical property of the tapered fiber TISA and high nonlinear fiber (HNLF), the fiber laser could operate at the pulse repetition of 3.125 GHz under 976 nm pump power of 148 mW, the pulse width of 1.754 ps, and the output power of 6.4 mW. Our results demonstrate that the tapered fiber TI device and HNLF can act as both high nonlinear optical component and SA in fiber lasers, and could also have better performance to achieve ultrashort pulses with ultrahigh repetition.