Fig. 1. (a) SEM images of the TI:Bi2Se3/PVA film with a resolution of 1 μm; (b) SEM images of the TI:Bi2Se3/PVA film with a resolution of 100 nm; (c) Raman spectrum of the TI:Bi2Se3/PVA film; (d) Raman spectrum of the TI:Bi2Se3 nanosheets.

Fig. 2. Nonlinear saturable absorption curve of the TI:Bi2Se3/PVA film.

Fig. 3. Experimental setup of dual-wavelength rectangular pulses fiber laser with a TI SA. EDF, erbium-doped fiber.

Fig. 4. Typical dual-wavelength rectangular pulse characteristics at the pump power of 90 mW; (a) output optical spectrum; (b) pulse train; (c) zoom-in single-pulse profile; (d) RF spectrum (inset, RF spectrum measured in 500 MHz range).

Fig. 5. (a) Output average power and pulse width; (b) pulse energy and peak power of rectangular pulse versus incident pump power.

Fig. 6. Typical time-domain characteristics of the rectangular pulse with different length of the SMF. Pulse train and corresponding single pulse profile of the rectangular pulse when (a) LSMF=63  m, β2,cavity=approximately−1.34  ps2; (b) LSMF=73  m, β2,cavity=approximately −1.57  ps2; (c) LSMF=93  m, β2,cavity=approximately−2.03  ps2; (d) LSMF=110  m, β2,cavity=approximately−2.42  ps2.

Fig. 7. Oscilloscope traces of first, second, third, and fifth HML of the dual-wavelength rectangular pulse when properly adjusting the pump power and the polarization state.