In the present work, the uniformly sized bismuthene quantum dots (BiQDs) with an average diameter of 26 nm were fabricated via the solvothermal approach. By transferring the BiQDs onto the plane of micro-machined D-shaped fiber (DSF), a new type of saturable absorber (SA) was successfully prepared. Based on the evanescent field effect of D-shaped fiber, the prepared SA exhibits excellent saturable absorption properties with the maximum modulation depth of 5.1% at around 1.5 μm. To further investigate its potential applications in ultrafast photonics, we demonstrated passive mode-locking operation in the erbium-doped fiber laser (EDFL) with BiQDs/DSF-SA. The conventional soliton pulses with duration of 835 fs at the repetition rate of 9.23 MHz and dissipative soliton pulses with duration of 575 fs at the repetition rate of 7.83 MHz were generated successfully. In addition, stable bound state of solitons with the pulse duration of 1.04 ps and sub-pulse time interval of 15.9 ps were also obtained based on the conventional soliton state by adjusting the pump power and polarization state. Our work reveals the great potential and capacity of BiQDs/DSF-SA in soliton mode-locking operations and promotes the explorative investigation of bismuth-based optoelectronic devices.

As a representative transition metal oxide, cupric oxide (CuO) has attracted a lot of interest in miscellaneous fields. In the present work, the prominent third-order nonlinear optical (NLO) features of CuO nanosheets were demonstrated via the typical Z-scan technique at 1 μm. The open-aperture (OA) Z-scan measurements at different intensities clearly showed that CuO nanosheets possessed the saturable absorption (SA), reverse saturable absorption (RSA) and optical limiting behaviors. The closed-aperture (CA) Z-scan technology was implanted to investigate the nonlinear refractive index and the third-order nonlinear susceptibility. In virtue of the strong nonlinear optical absorption properties of CuO nanosheets, a stable all-solid-state mode-locked laser with the as-prepared CuO nanosheets as saturable absorber at 1.06 μm was realized for the first time. Our work confirmed that CuO nanosheets exhibited outstanding NLO properties, which might stimulate the development in ultrafast photonics and nonlinear optics.