Ge-Rich SiGe Mode-Locker for Erbium-Doped Fiber Lasers

A nonstoichiometric Si
_1-x
Ge
_x
with composition ratio dependent saturable absorption prepared by vaporized synthesis and chemical exfoliation is performed to passively mode-lock the Erbium-doped fiber laser (EDFL). The Si
_1-x
Ge
_x
with varied Ge/Si composition ratio from 3 to 16 exhibits tunable nonlinear modulation depth from 17% to 22%, where the Si
_1-x
Ge
_x
with the highest Ge content performs the largest nonlinear modulation depth. When operating the EDFL in the self-amplitude modulation region, the Si
_1-x
Ge
_x
with Ge/Si composition ratios of 3, 9, and 16 self-starts the EDFL pulsation with pulsewidths of 820, 760, and 730 fs. When operating the EDFL in high gain region, the self-phase modulation induced soliton compression dominates the repulsation of passively mode-locked EDFL, which slightly shrinks the EDFL pulsewidth from 346 to 338 fs. All these demonstrations are premier and important to explore the superior nonstoichiometric Si
_1-x
Ge
_x
saturable absorbers for ultrafast fiber lasers.