Fe₂O₃ nanomaterials, as one of the transition metal oxides (TMOs) materials, have garnered attention in ultrafast photonics due to their robust third-order nonlinearity, rapid carrier recovery time, high stability, broad absorption bandwidth and straightforward preparation methods. In order to further enhance the performance of Fe₂O₃ nanomaterials, oxygen vacancy defects were introduced in the process of preparing the Fe₂O₃ nanomaterials in this paper. By characterizing the nonlinear optical properties of the prepared Fe₂O₃ nanomaterials with different surface oxygen vacancy concentrations, we found that Fe₂O₃ nanomaterials with larger oxygen vacancy content have a deeper modulation depth and the larger third-order nonlinear coefficient. It also indicated that the incorporation of oxygen vacancy defects can significantly enhance the nonlinear optical properties of Fe₂O₃ nanomaterials. Furthermore, the ultrafast carrier dynamics of Fe₂O₃ materials with varying concentrations of oxygen vacancies were investigated using femtosecond-resolved transient absorption (TA) spectroscopy, elucidating the microscopic mechanism. Finally, we inserted Fe₂O₃-based saturable absorbers into Yb- and Er-doped fiber lasers. Noise-like mode-locking operation and multi-pulse mode-locking operation are realized at 1 μm in the Yb-doped fiber laser. Besides, the conventional soliton mode-locking operations with different central wavelengths are realized within 1.5 μm band in an Er-doped fiber laser.

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.

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.