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 mu m. 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 mu m, 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.