A new type of saturable absorber (SA) based on indium tin oxide (ITO) nanocrystals for passively Q-switched erbium-doped fiber (EDF) laser has been demonstrated experimentally. High quality ITO nanocrystals were prepared by the coprecipitation method. As a degenerate oxide semiconductor, the ITO has a wide range of saturable absorption regions, strong plasmonic absorption peaks, and ultra-fast recovery time. The nonlinear absorption properties of ITO are investigated by a balanced twin-detector measurement system. The saturation intensity and modulation depths are 9.87 MW/cm² and 0.83%, respectively. We successfully fabricated ITO SAs by depositing the ITO dispersion solution at the end of a fiber connector. By inserting the ITO SAs into an EDF fiber cavity, stable passively Q-switched pulses with the minimum pulse width of 1.15 μs under a repetition rate of 81.28 kHz were obtained. The maximum output power of 1722 μW and pulse energy of 21.19 nJ were realized when the pump power was 480 mW at the wavelength of 1530.3 nm. The results suggest that ITO nanocrystals are expected to develop into another effective SA for ultrafast photonics.

We demonstrate the generation of versatile mode-locked operations in an Er-doped fiber laser with an indium tin oxide (ITO) saturable absorber (SA). As an epsilon-near-zero material, ITO has been only used to fashion a mode-locked fiber laser as an ITO nanoparticle-polyvinyl alcohol SA. However, this type of SA cannot work at high power or ensure that the SA materials can be transmitted by the light. Thus, we covered the end face of a fiber with a uniform ITO film using the radio frequency magnetron sputtering technology to fabricate a novel ITO SA. Using this new type of SA, single-wavelength pulses, dual-wavelength pulses, and triple-wavelength multi-pulses were achieved easily. The pulse durations of these mode-locked operations were 1.67, 6.91, and 1 ns, respectively. At the dual-wavelength mode-locked state, the fiber laser could achieve an output power of 2.91 mW and a pulse energy of 1.48 nJ. This study reveals that such a proposed film-type ITO SA has excellent nonlinear absorption properties, which can promote the application of ITO film for ultrafast photonics.

In this manuscript, the nonlinear absorption properties of Cr₂Ge₂Te₆ and its application in ultra-fast optical modulation are investigated. Typical parameters, namely, nonlinear absorption coefficient (β), saturation intensity, and modulation depth are measured to be ~1.66 × 10⁻⁹ m/W, 15.3 MW/cm², and 5.8%, respectively. To investigate the feasibility of using the Cr₂Ge₂Te₆ as an ultra-fast optical modulator, a ring-cavity passively mode-locked Er-doped fiber laser has been constructed. The output power/pulse, duration/pulse, and repetition rate/signal-to-noise ratios for the stable mode-locked operation are 2.88 mW/881 fs/19.33 MHz/48 dB, respectively, which proves that the Cr₂Ge₂Te₆ has outstanding nonlinear optical properties and advantages in performing as an ultra-fast optical modulator. Further, the experimental results provide valuable references and open new avenues for developing two-dimensional, material-based, ultra-fast optical modulators and advanced photonic devices based on Cr₂Ge₂Te₆.

Recently, two-dimensional (2D) materials have been widely studied by researchers due to their exceptional 2D structure and excellent optical characteristics. As one of the typically-layered 2D transition metal dichalcogenide (TMD) semiconductors from group IVB with a bandgap value of 0.9–1.2 eV (bulk to monolayer), the characteristics of zirconium diselenide (ZrSe₂) have already been extensively investigated in many fields. However, the nonlinear absorption properties of ZrSe₂ in ultra-fast lasers have not been previously demonstrated. In this work, we measured various parameters in order to investigate the characteristics of the nonlinear saturable absorption of ZrSe₂. A ZrSe₂–polyvinyl alcohol (PVA) film was successfully prepared, which was employed as a saturable absorber (SA) to demonstrate, for the first time, an erbium (Er)-doped passive mode-locking fiber laser with a ring cavity. The saturation intensity of the ZrSe₂–PVA film-type SA is 12.72 MW/cm², while its modulation depth is 2.3%. The stable soliton state with a maximum output power of 11.37 mW and a narrowest monopulse duration of 12.5 ps at a repetition frequency of 21.22 MHz was detected. The experimental results conclusively proved that ZrSe₂, with its suitable bandgap value and excellent nonlinear absorption properties, as well as its high damage threshold, should have extensive potential applications within the field of ultra-fast pulse lasers.

In our work, based on a high-damage-threshold MoS₂ saturable absorber (SA), high-power intra-cavity Raman solitons within a passively mode-locked Yb-doped fiber laser were demonstrated successfully for the first time. The damage threshold of the MoS₂ SA was as high as ~0.48 J/cm². By adjusting the polarization states, stable single- or dual-pulse Raman soliton operations were obtained. The maximum average output power for single-pulse and dual-pulse Raman soliton operations was 80.11 and 89.33 mW, respectively. Our experiment results show significant enhancement in comparison with previous works, which provides fundamental guidance for future designs of high-power, large-energy, intra-cavity Raman soliton generations based on two-dimensional materials as SAs.