Amorphous oxides have unique physicochemical properties with extensive opto-electronic applications such as the thin-film transistor, light-emitting diode backplanes, and supercontinuum generation. In this contribution, we synthesize the amorphous ZrO₂/SiO₂ nanoporous aerogel with high structural integrity. With the femtosecond excitation laser at 800–1,064 nm, the broadband second harmonic generation is observed. The nonlinear optical properties of the as-prepared ZrO₂/SiO₂ aerogel are investigated at 1.0 μm and 1.5 μm for the first time. Subsequently, the amorphous ZrO₂/SiO₂ saturable absorber is originally applied in the Yb-doped and Er-doped fiber lasers to realize the mode-locking operations. In the Yb-doped fiber laser, the dissipative soliton resonance mode-locking operation is demonstrated with the largest pulse duration of 22 ns at a repetition rate of 7.8 MHz and a high signal-to-noise ratio of 64 dB. In the Er-doped fiber laser, a conventional soliton mod-locking regime is observed with an ultrashort pulse width of 960 fs, a repetition frequency of 6.55 MHz, and a time-bandwidth production of 0.347. Our work shows the good ability of the ZrO₂/SiO₂ aerogel in generating ultrafast pulses and extends the saturable absorber into the amorphous material realm.

Here, we investigated the nonlinear optical (NLO) characteristics of carboxyl-functionalized graphene oxide (GO-COOH) in the near-infrared (NIR) region. The results revealed that GO-COOH samples exhibit strong saturable absorption at low pump levels and a gradual transition to reverse saturable absorption (RSA) with increasing pump power. Then the saturable absorber (SA) by depositing the GO-COOH on the side-polished fiber (SPF) was employed in Yb- and Er-doped fiber lasers. Stable ultrashort pulses operating in the dissipative soliton (DS) and conventional soliton (CS) regimes were obtained with pulse widths of 26.6 ps and 968 fs, respectively. Besides, the dissipative soliton resonance (DSR) phenomenon caused by the RSA of GO-COOH was also observed with increasing pump power. The high-stable DSR mode-locked pulses with the maximum pulse energy of 1.91 nJ and 0.74 nJ were obtained in YDFL and EDFL respectively. These results not only reveal the potentiality of GO-COOH in ultrafast photonics applications but also open a new avenue to explore high-pulse-energy laser sources based on two-dimensional materials.

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.