  Two-dimensional mono-elemental material is an excellent saturable absorber
candidate with low saturation intensity, large modulation depth, high
nonlinearities, and fast recovery time of excited carriers. Typically, these
mono-elemental material with two-dimensional structure possesses tunable
bandgap from metallic to semiconducting according to different number of
layers. The successful application of these materials as the saturable absorber
has exploited the development of mode-locked fiber lasers. Therefore, this
review is intended to provide an up-to-date information to the development of
mono-elemental saturable absorber for the advances in mode-locked fiber laser,
with emphasis on their material properties, synthesis process and material
characterization. Meanwhile, issues and challenges of the review research topic
will be highlighted and addressed with several concrete recommendations.
