Recently, ultrafast optical modulators (OMs) based on atomic transition-metal dichalcogenides (TMDs) film have been intensively explored. Benefited from their remarkable nonlinear saturable absorption properties, TMDs based OMs could be employed as critical devices for pulsed lasers systems to transit continuous wave into pulse trains in laser cavity. Herein, the few-layer TMDs films were grown by chemical vapor deposition (CVD) method in possession of uniform thickness, large areas and high crystal quality. Then two types TMDs based OMs were fabricated by integrating single TMDs film or van der waals heterostructures (VdWHs) on the target substrates. As for VdWHs based OMs, different few-layer TMDs films were vertically stacked in turns on the target substrates to form heterointerfaces, which has been demonstrated with ultrafast carrier relaxation time between neighbor layers recently and is favor for ultrafast pulse generation. In our experiments, the nonlinear optical properties of two types TMDs based OMs were systematically investigated by measuring their nonlinear saturable absorption curves and further compared by embedded them into same fiber laser systems. The results indicate that the VdWHs based OMs owns more excellent nonlinear optical properties (such as larger modulation depth, smaller saturable intensity) and offers a feasible strategy to engineer desired ultrafast photonics devices by modifying the structure of VdWHs.
We propose two schemes for achieving tungsten disulfide (WS2)-based saturable absorber (SA) and saturable absorber mirror (SAM). By utilizing the pulsed laser deposition method, we grow the WS2 film on microfiber to form an evanescent field interaction SA device. Incorporating this SA device into a common ring-cavity erbium-doped fiber (EDF) laser, stably passive mode-locking can be achieved with pulse duration of 395 fs and signal-to-noise ratio of 64 dB. We also produce a fiber tip integrated WS2-SAM by utilizing the magnetron sputtering technique (MST). This new type of SAM combines the WS2 layer as SA and gold mirror as high reflective mirror. By employing the WS2-SAM, we construct the linear-cavity EDF lasers, and achieve passive mode-locking operation with pulse duration of ∼1 ns and SNR of ∼61 dB. We further achieve stably passive Q-switching operation with pulse duration of ∼160 ns and pulse energy of 54.4 nJ. These fiber-integrated SAs and SAMs have merits of compactness and reliability, paving the way for the development of new photonic devices such as SAs for pulsed laser technology.