WS2 as a saturable absorber for ultrafast photonic applications of mode-locked and Q-switched lasers

摘要

Two-dimensional (2D) nanomaterials, especially the transition metal sulfidesemiconductors, have drawn great interests due to their potential applicationsin viable photonic and optoelectronic devices, such as saturable absorbers(SAs) and optical switches, etc. In this work, tungsten disulfide (WS2) basedSA for ultrafast photonic applications was demonstrated. WS2 nanosheets wereprepared using liquid-phase exfoliation method and embedded in polyvinylalcohol (PVA) thin film for the practical usage. Saturable absorption wasobserved in the WS2-PVA SA at the telecommunication waveband near 1550 nm. Byincorporating WS2-PVA SA into a fiber laser cavity, both stable mode lockingoperation and Q-switching operation were achieved. In the mode lockingoperation, the laser obtained femtosecond output pulse width and high spectralpurity in the radio frequency spectrum. In the Q-switching operation, the laserhad tunable repetition rate and output pulse energy of a few tens of nanojoule. Our findings suggest that few-layer WS2 nanosheets embedded in PVA thinfilm are promising nonlinear optical materials for ultrafast photonicapplications as a mode locker or Q-switcher.