Two-dimensional layered monoelemental materials (Xenes) with excellent optoelectronic properties have various property-related applications, such as energy, biomedicine, and optoelectronic devices. Xenes also show excellent performance in acting as saturable absorbers (SAs) for obtaining ultrafast laser operations. Few-layer tellurene as a typical Xenens exhibits distinct optoelectronic properties and promising practical application potential, and its nonlinear optical absorption characteristics and related ultrafast modulation applications have been investigated preliminarily. However, tellurene-based SAs to demonstrate large-energy mode-locked operations, which have special applications in industrial and scientific research areas, are seldom studied. In this work, we focus on the preparation of tellurene-based SAs and explore its applications in demonstrating large-energy mode-locked operations [dissipative soliton (DS) and noise-like pulses (NLP)]. For DS operation, the maximum average output power, pulse width, and largest pulse energy are 23.61 mW, 5.87 ps, and 1.94 nJ, respectively. NLP operation with a recorded average output power of 106.6 mW and a pulse energy of 8.76 nJ is also generated, which shows significant enhancement in comparison to previously reported Xenes-based works. Our contribution reveals the great potential and capacity of tellurene-based SAs in obtaining large-energy pulse operations and further promotes the explorative investigation of Xenes-based optoelectronic devices.

Driven by new two-dimensional materials, great changes and progress have taken place in the field of ultrafast photonics in recent years. Among them, the emerging single element two-dimensional materials (Xenes) have also received much attention due to their special physical and photoelectric properties including tunable broadband nonlinear saturable absorption, ultrafast carrier recovery rate, and ultrashort recovery time. In this review, the preparation methods of Xenes and various integration strategies are detailedly introduced at first. Then, we summarize the outcomes achieved by Xenes-based (beyond graphene) fiber lasers and make classifications based on the characteristics of output pulses according to the materials characterization and nonlinear optical absorption properties. Finally, an outlook of the future opportunities and challenges of ultrafast photonics devices based on Xenes and other 2D materials are highlighted, and we hope this review will promote their extensive applications in ultrafast photonics technology.

Layered transition metal dichalcogenides with excellent nonlinear absorption properties have shown remarkable performance in acting as ultrafast photonics devices. In our work, palladium diselenide (PdSe2) nanosheets with competitive advantages of wide tunable bandgap, unique puckered pentagonal structure and excellent air stability are prepared by the liquid-phase exfoliation method. Its ultrafast absorption performance was verified by demonstrating conventional and dissipative soliton operations within Er-doped fiber lasers. The minimum pulse width of the conventional soliton was 1.19 ps. Meanwhile, dissipative soliton with a 46.67 mW output power, 35.37 nm spectrum width, 14.92 ps pulse width and 2.86 nJ pulse energy was also generated successfully. Our enhanced experiment results present the excellent absorption performance of PdSe2 and highlight the capacity of PdSe2 in acting as ultrafast photonics devices.

In our work, passively mode-locked and Q-switched Er-doped fiber lasers (EDFLs) based on titanium disulfide (TiS2) as a saturable absorber (SA) were generated successfully. Stable mode-locked pulses centred at 1531.69 nm with the minimum pulse width of 2.36 ps were obtained. By reducing the length of the laser cavity and optimizing the cavity loss, Q-switched operation with a maximum pulse energy of 67.2 nJ and a minimum pulse duration of 2.34 µs was also obtained. Its repetition rate monotonically increased from 13.17 kHz to 48.45 kHz with about a 35 kHz tuning range. Our experiment results fully indicate that TiS2 exhibits excellent nonlinear absorption performance and significant potential in acting as ultra-fast photonics devices.

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In our work, Cr2Si2Te6, a novel two-dimensional (2D)-layered ferromagnetic insulator, was used as a saturable absorber (SA) for demonstrating a pulsed Er-doped fiber laser (EDFL) based on its nonlinear saturable absorption properties. The modulation depth and saturation intensity of the Cr2Si2Te6-based SA are 6.61% and 10.77 MW/cm2, respectively. When the pump power is 60.3 mW, the 13th harmonic mode-locked generation is obtained, the 3 dB optical spectrum bandwidth is 1.392 nm and the central wavelength is 1568.032 nm. When the pump power is higher than 170.3 mW, the EDFL works at the fundamental repetition frequency of 1.23 MHz with a signal-to-noise ratio of 25 dB. The experimental results reveal that Cr2Si2Te6 SA has enormous potential in demonstrating ultrafast fiber lasers and provide references for future research based on Cr2Si2Te6 as ultrafast optical modulators.

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