Owing to the specific two-dimensional (2D) confinement of electron motion and the absence of interlayer perturbation, 2D semiconductors possess unique optoelectronic properties and has become a research hot-spot in recent years. Recently, Prof. Jun Wang at Shanghai Institute of Optics and Fine Mechanics and his collaborators reported for the first time the outstanding ultrafast saturable absorption performance in 2D layered MoS₂ nanomaterials in the near infrared wavelength band. The results have been published in "American Chemical Society - Nano" (ACS Nano, 7, 9260 (2013)). Realized that the sizable and thickness-dependent bandgap offers the layered transition metal dichalcogenides, say, MoS₂, MoSe₂, WS₂, etc., a huge potential in the development of photonic devices with high performance and unique functions, Dr. Wang and his co-workers successfully prepared 2D MoS₂ dispersions with high-quality layered nanosheets using liquid-phase exfoliation technology, and showed that the ultrafast saturable absorption performance of the MoS₂ nanosheets is more excellent than that of graphene for fs pulses in the near infrared region. The exciting results open up the door to 2D photonic nano-devices, such as optical switches, pulse shaping devices, mode-lockers, optical limiters, etc., capable of ultrafast response and broadband tunability.