SnS nanosheets for harmonic pulses generation in near infrared region

Ultrafast optical properties and applications of anisotropic 2D materials

Two-dimensional (2D) layered materials exhibit strong light-matter interactions, remarkable excitonic effects, and ultrafast optical response, making them promising for high-speed on-chip nanophotonics. Recently, significant attention has been directed towards anisotropic 2D materials (A2DMs) with low in-plane crystal symmetry. These materials present unique optical properties dependent on polarization and direction, offering additional degrees of freedom absent in conventional isotropic 2D materials. In this review, we discuss recent progress in understanding the fundamental aspects and ultrafast nanophotonic applications of A2DMs. We cover structural characteristics and anisotropic linear/nonlinear optical properties of A2DMs, including well-studied black phosphorus and rhenium dichalcogenides, as well as emerging quasi-one-dimensional materials. Then, we discuss fundamental ultrafast anisotropic phenomena occurring in A2DMs, such as polarization-dependent ultrafast dynamics of charge carriers and excitons, their direction-dependent spatiotemporal diffusion, photo-induced symmetry switching, and anisotropic coherent acoustic phonons. Furthermore, we review state-of-the-art ultrafast nanophotonic applications based on A2DMs, including polarization-driven active all-optical modulations and ultrafast pulse generations. This review concludes by offering perspectives on the challenges and future prospects of A2DMs in ultrafast nanophotonics.

2D van der Waals materials for ultrafast pulsed fiber lasers: review and prospect

2D van der Waals materials are crystals composed of atomic layers, which have atomic thickness scale layers and rich distinct properties, including ultrafast optical response, surface effects, light-mater interaction, small size effects, quantum effects and macro quantum tunnel effects. With the exploration of saturable absorption characteristic of 2D van der Waals materials, a series of potential applications of 2D van der Waals materials as high threshold, broadband and fast response saturable absorbers (SAs) in ultrafast photonics have been proposed and confirmed. Herein, the photoelectric characteristics, nonlinear characteristic measurement technique of 2D van der Waals materials and the preparation technology of SAs are systematically described. Furthermore, the ultrafast pulsed fiber lasers based on classical 2D van der Waals materials including graphene, transition metal chalcogenides, topological insulators and black phosphorus have been fully summarized and analyzed. On this basis, opportunities and directions in this field, as well as the research results of ultrafast pulsed fiber lasers based on the latest 2D van der Waals materials (such as PbO, FePSe₃, graphdiyne, bismuthene, Ag₂S and MXene etc), are reviewed and summarized.

Ultrafast Photonics of Ternary RexNb(1-x)S2 in Fiber Lasers

Two-dimensional (2D) transition metal chalcogenides (TMCs) become more attractive upon addition of a third element owing to their unique structure and remarkable physical and chemical properties, which endow these materials with considerable potential for applications in nanoscale devices. In this work, a Re_xNb_(1-x)S₂-based saturable absorber (SA) device for ultrafast photonics applications is studied. The device is assembled by placing Re_xNb_(1-x)S₂ nanosheets with a thickness of 1-3 nm onto a microfiber to increase their compatibility with an all-fiber laser cavity. The prepared Re_xNb_(1-x)S₂-based device exhibits a modulation depth of 24.3%, a saturation intensity of 10.1 MW/cm², and a nonsaturable loss of 28.5%. Furthermore, the Re_xNb_(1-x)S₂-based device is used to generate ultrashort pulses in an erbium-doped fiber (EDF) laser cavity. At a pump power of 260 mW, the EDF laser operates in a conventional soliton mode-locked region. The pulse width is 285 fs, and the repetition frequency is 61.993 MHz. In particular, the bound-state soliton mode-locking operation is successfully obtained in a pump power range of 300-900 mW. The bound-state pulses are formed by doubling identical solitons with a temporal interval of 0.8 ps. The output power is as high as 47.9 mW, and the repetition frequency is 123.61 MHz. These results indicate that the proposed Re_xNb_(1-x)S₂-based SAs have comparable properties to currently used 2D SAs and provide a basis for their application in the field of ultrafast photonics.

Facile synthesis of the crescent-like SnS nanocrystals capped by polyvinyl pyrrolidone and its performance of adsorbing dyes

With using Sn²⁺ as tin source, l-cysteine as sulphur source and polyvinyl pyrrolidone (PVP, M_w = 1300000) as surfactant, a novel three-dimensional and crescent-like SnS nanocrystal (NCs) was successfully synthesized in a one-pot hydrothermal method. The as-prepared SnS NCs displayed uniform crescent-like morphological structure, and demonstrated excellent efficiency for the adsorption of cationic dyes such as rhodamine B (RhB) and methylene blue (MB). Kinetic analysis indicated that the adsorption process followed the pseudo second-order model, and the maximum capacity of the SnS NCs to adsorb MB was determined by Langmuir equation to be 252 mg⋅g^-1 at 298 K. The pH dependence of SnS NCs on the adsorption of cationic dyes and the characterization of zeta potential jointly suggested the existence of electrostatic attraction in the process. Overall, this study showed that electrostatic field of functional groups and the capping of PVP could significantly enhance the adsorption performance of the SnS NCs, and also provides a novel insight into the development of highly efficient inorganic adsorbents for cationic dyes.

WxNb(1-x)Se2 nanosheets for ultrafast photonics

Ternary transition metal chalcogenides (TTMDCs), a novel type of two-dimensional (2D) three-element materials, possess multiple physical and chemical properties and have promising potentials in basic physics and devices. Herein, the usage of W_xNb_(1-x)Se₂ nanosheets as a rising ultrafast photonic device to generate high power mode-locked and Q-switched pulses in a fiber laser is demonstrated. The W_xNb_(1-x)Se₂ nanosheets were successfully prepared by the liquid exfoliation method with thickness less than 3 nm. The nonlinear optical absorption of the W_xNb_(1-x)Se₂-based device was investigated with the saturable intensity of 40.93 MW cm^-2 and modulation depth of 5.43%. After integrating the W_xNb_(1-x)Se₂-based device into an Er-doped fiber (EDF) laser cavity, mode-locking and Q-switching laser pulses were formed. In the mode-locked mechanism output, the pulse width is as narrow as 131 fs and the output power is 52.93 mW. In Q-switched operation, the shortest pulse duration is 1.47 μs with the largest pulse energy of 257 nJ. Compared to recent studies, our results showed some improvements. This study suggests that 2D TTMDC-based devices could be developed as efficient ultrafast photonics candidates and widely used in nonlinear optical applications.

Indium selenide saturable absorber for high-energy nanosecond Q-switched pulse generation

As a kind of III/VI group compound 2D layered material, indium selenide (In₂Se₃) has attracted tremendous interest because of its favorable optoelectronic characteristics. Here, magnetron sputtering deposition (MSD) technology was employed to prepare an In₂Se₃-based saturable absorber (SA). The nonlinear optical properties of this SA, whose modulation depth (ΔT) is 6.18%, were studied. With the aid of its saturable absorption, a stable two-wavelength Q-switching Er-doped fiber (EDF) laser was established. When pump power was adjusted to 900 mW, the output power was increased to 63.84 mW. The shortest pulse duration and maximum pulse energy were estimated to be 556 ns and 376 nJ, respectively. The signal-to-noise ratio of 70 dB proves this fiber laser has high stability. In comparison with previous works, the laser performance in this study is improved significantly. These results indicate that the In₂Se₃ holds promise as an outstanding candidate for high-energy pulse generation and will advance the development of In₂Se₃-based nonlinear photonics devices.