# Saturable Absorption Dynamics of Highly Stacked 2D Materials for Ultrafast Pulsed Laser Production
## 4 Topological Insulator SAs
### TI SAs for Dissipative Soliton Resonance Lasers  
Through extensive investigation on mode-locked fiber lasers performed over recent decades, it was discovered that five different types of pulses can appear in the fiber cavity via mode-locking, depending on the interplay between the Kerr effect and group velocity dispersion, which are the conventional solution [68; 69], stretched pulse [70], similariton [71], dissipative soliton [72; 73] and dissipative soliton resonance [74]. In a normal dispersion regime, dissipative soliton pulses with a broad temporal width can be produced through proper interaction among gain, loss, dispersion, optical nonlinearity and spectral filtering. Dissipative soliton is known to have much higher energy than conventional soliton pulses. However, even though they can generate laser pulses with a large energy, they suffered from an energy scaling issue due to pulse splitting phenomenon as the pump power become higher. [PERSON] et al. [74] theoretically predicted that another type of mole-locked pulses, referred as dissipative soliton resonance, could also be generated under a normal dispersion condition, which was actually validated through a number of continued experiments. This laser typically produces flat-top, square-shaped pulses with a temporal width that can extend limitlessly as the pump power increases. In the dissipative soliton resonance, a pulse peak power is clamped and maintained, while its pulse energy monotonously increases as the pump power increases. Furthermore, in-depth investigation reveals that dissipative soliton resonance can occur in both the normal and anomalous dispersion spectral regions of the medium, while dissipative soliton only occurs in the normal dispersion region. To induce the dissipative soliton resonance, various factors including saturable absorption, gain, propagation loss, Kerr effect and dispersion should be properly adjusted to obtain the desired balance. Several conditions of cavity parameters were reported for the occurrence of dissipative soliton resonance, but optimum SA parameters are yet elucidated. One obvious point is that the modulation depth should be large enough to generate the mode-locked pulses in the normal dispersion region. [PERSON] et al. demonstrated that pulse-width-tunable, a mode-locked fiber laser through dissipative soliton resonance could be manufactured using a highly stacked Bi\({}_{2}\)Ti\({}_{3}\) TI to emphasize its prominent potential in SA applications [75]. For this operation, a ring-cavity fiber laser system was constructed consisting of a 6-m-long Er-doped fiber (EDF), 980/1550 nm and 1480/1550 nm WDMs, a polarization controller, an optical isolator, 1480-nm and 980-nm pump LDs, a 30:70 output coupler and most importantly a 100-m long dispersion compensating fiber (DCF) along with the incorporation of a highly stacked  
Figure 13: (a) Measured optical spectrum of amplified pulses. (b) Measured autocorrelation trace. Reprinted with permission from [66]. Bi\({}_{2}\)Te\({}_{3}\) SA module (Figure 14). Compared to normal configuration of mode-locked lasers, two points are noticeable. First, for sufficient increase of output pulse energy, two laser diodes with the wavelength of 1480 nm and 980 nm were used and their maximum pump powers were 82 mW and 298 mW, respectively. Second, a 100-m long DCF with a normal dispersion of \(-\)98 ps/nm km at 1550 nm was employed to enhance dissipative soliton resonance while suppressing the conventional soliton evolution. The power of the 1480-nm LD was gradually increased up to the maximum amount of 298 mW to launch the pump power while keeping the 980-nm LD switched off, and subsequently the 980-nm LD was switched on to further increase the pump power to supply a sufficient power to the gain fiber. Conventional mode-locked pulsed lasers with a nanosecond duration were first obtained at the pump power of 88 mW, using a 1480-nm LD only.