Graphene-like two dimensional materials, such as WS₂ and MoS₂, are highly anisotropic layered compounds that have attracted growing interest from basic research to practical applications. Similar with MoS₂, few-layer WS₂ has remarkable physical properties. Here, we demonstrate for the first time that WS₂ nanosheets exhibit ultrafast nonlinear saturable absorption property and high optical damage threshold. Soliton mode-locking operations are achieved separately in an erbium-doped fiber laser using two types of WS₂-based saturable absorbers, one of which is fabricated by depositing WS₂ nanosheets on a D-shaped fiber, while the other is synthesized by mixing WS₂ solution with polyvinyl alcohol, and then evaporating them on a substrate. At the maximum pump power of 600 mW, two saturable absorbers can work stably at mode-locking state without damage, indicating that few-layer WS₂ is a promising high-power flexible saturable absorber for ultrafast optics. Numerous applications may benefit from the ultrafast nonlinear features of WS₂ nanosheets, such as high-power pulsed laser, materials processing, and frequency comb spectroscopy.

Transition-metal dichalcogenides, such as tungsten disulfide (WS₂) and molybdenium disulfide (MoS₂), are highly anisotropic layered materials and have attracted growing interest from basic research to practical applications due to their exotic physical property that may complement graphene and other semiconductor materials. WS₂ nanosheets are found to exhibit broadband nonlinear saturable absorption property, and saturable absorbers (SAs) are fabricated by depositing WS₂ nanosheets on side-polished fibers. Attributing to the weak evanescent field and long interaction length, the WS₂ nanosheets are not exposed to large optical intensity, which allows the SA to work at the high-power regime. The SAs are used to mode lock erbium- and ytterbium-doped fiber lasers with normal dispersion, producing trains of dissipative soliton at 1.55 and 1.06 µm respectively. Simulations show that the bandgap of WS₂ nanosheets decreases from 1.18 to 0.02 and 0.65 eV by introducing W and S defects respectively, which may contribute to the broadband saturable absorption property of the WS₂.

Few-layer transition-metal dichalcogenide WSe₂/MoSe₂ nanosheets are fabricated by a liquid exfoliation technique using sodium deoxycholate bile salt as surfactant and their nonlinear optical properties are investigated based on a balanced twin-detector measurement scheme. It is demonstrated that both types of nanosheets exhibit nonlinear saturable absorption properties at the wavelength of 1.55 μm. By depositing the nanosheets on side polished fiber (SPF) or mixing the nanosheets with polyvinyl alcohol (PVA) solution, SPF-WSe₂ saturable absorber (SA), SPF-MoSe₂ SA, PVA-WSe₂ SA and PVA-MoSe₂ SA are successfully fabricated and further tested in erbium-doped fiber lasers. The SPF-based SA is capable of operating at the high pump regime without damage and a train of 3252.65 MHz harmonically mode-locked pulses are obtained based on the SPF-WSe₂ SA. Soliton mode locking operations are also achieved in the fiber laser separately with other three types of SAs, confirming that the WSe₂ and MoSe₂ nanosheets could act as cost-effective high-power SAs for ultrafast optics.

We present a kind of harmonic mode locking of bound-state solitons in a fiber laser based on molybdenum disulfide (MoS₂) saturable absorber (SA). The mode locker is fabricated by depositing MoS₂ nanosheets on a D-shaped fiber (DF). In the fiber laser, two solitons form the bound-state pulses with a temporal separation of 3.4 ps, and the bound-state pulses are equally distributed at a repetition rate of 125 MHz, corresponding to 14th harmonics of fundamental cavity repetition rate (8.968 MHz). Single- and multiple-pulses emissions are also observed by changing the pump power and optimizing the DF based MoS₂ SA. Our experiment demonstrates an interesting operation regime of mode-locked fiber laser, and shows that DF based MoS₂ SA can work as a promising high-power mode locker in ultrafast lasers.

Transition‐metal dichalcogenides (TMDCs) and black phosphorus (BP) are typical 2D materials with layer‐dependent bandgaps, which are emerging as promising saturable absorption materials for pulsed fiber lasers. In this review, we discuss the nonlinear saturable absorption properties of TMDCs and BP, and summarize the recent progress of saturable absorbers from fabrication methods to incorporation strategies. The performances of saturable absorbers and the properties of Q‐switched/mode‐locked fiber lasers at different wavelengths are summarized and compared to give a comprehensive insight to optical modulators based on TMDCs/BP, and to promote their practical applications in nonlinear optics.