Nonlinear optical response and application of WS₂ saturable absorber

The rediscovered high-mobility 2D layer material WS₂, with a graphite-like layered structure, has attracted much attention for electronics and optoelectronics applications and is being intensively investigated as a candidate in various photonics applications. In this study, we demonstrate that WS₂ exhibits nonlinear optical response and serves as an effective saturable absorber (SA) at 1.55 μm. Using the pulsed laser deposition method, few-layer WS₂ is deposited on the side surface of a tapered fiber. The tapered fiber has small waist diameter of 12 μm, and the effective length of the taper zone is 3 mm. Thus, the evanescent field interaction scheme has the ability to further raise the optical damage threshold as well as enhance the nonlinearity. The nonlinear optical response of a WS₂-clad microfiber SA device is investigated. The modulation depth is measured to be 9.16%. Stable mode-locking operation is realized in an erbium-doped fiber laser with wide pump range by utilizing the proposed WS₂-based SA device. The pulse duration and maximum output power are measured to be 1.35 ps and 20.88 mW, respectively. The obtained results effectively show that WS₂ has great potential for future practical use in photonics, such as visible/near-infrared pulsed lasers, materials processing, optical sensors, and modulators.