“…Several types of SAs have been investigated to realize passive mode-locked fiber lasers, such as semiconductor SA mirrors [6,7], carbon nanotubes [8][9][10], graphene [11][12][13], transition metal dichalcogenides [14][15][16][17], topological insulators [18,19], and metal nanoparticles [20][21][22]. In this regard, transition metal oxide (TMO)-based SAs have now emerged as a new branch of SA materials due to their wide absorption band induced by surface plasmon resonance, large nonlinearity, high optical damage threshold and fast recovery time [23][24][25][26][27][28]. Zinc oxide (ZnO), titanium dioxide (TiO 2 ), Nickel oxide (NiO), and copper oxide (CuO) have been fabricated and investigated as SAs for pulsed lasers [24,25,29,30].…”