In this work, a soliton mode-locked erbium-doped fiber laser (EDFL) with a high-quality molecular beam epitaxy (MBE)-grown topological insulator (TI) Bi₂Se₃ saturable absorber (SA) is reported. To fabricate the SA device, a 16-layer Bi₂Se₃ film was grown successfully on a 100 μm thick SiO₂ substrate and sandwiched directly between two fiber ferrules. The TI-SA had a saturable absorption of 1.12% and a saturable influence of 160 MW/cm². After inserting the TI-SA into the unidirectional ring-cavity EDFL, self-starting mode-locked soliton pulse trains were obtained at a fundamental repetition rate of 19.352 MHz. The output central wavelength, pulse energy, pulse duration, and signal to noise ratio of the radio frequency spectrum were 1530 nm,18.5 pJ, 1.08 ps, and 60 dBm, respectively. These results demonstrate that the MBE technique could provide a controllable and repeatable method for the fabrication of identical high-quality TI-SAs, which is critically important for ultra-fast pulse generation.

We demonstrate a multiwavelength Tm-doped fiber laser employing polarization-maintaining undoped fiber (PMF) based on nonlinear polarization rotation. The PMF and a polarization-sensitive isolator between two polarization controllers are used to induce the intensity-dependent loss and frequency-dependent loss to alleviate mode competition caused by homogeneous gain broadening in an active fiber. An up to four wavelengths laser operating in a cavity is observed without the PMF. After the PMF is inserted into the cavity, stable dual-wavelength operation is achieved. The output had an average power distribution. The spectral fluctuation at each wavelength is smaller than 0.9 dB.