Passivation of black phosphorus saturable absorbers for reliable pulse formation of fiber lasers

Ultrafast Fiber Lasers with Low-Dimensional Saturable Absorbers: Status and Prospects

Wide-spectral saturable absorption (SA) in low-dimensional (LD) nanomaterials such as zero-, one-, and two-dimensional materials has been proven experimentally with outstanding results, including low saturation intensity, deep modulation depth, and fast carrier recovery time. LD nanomaterials can therefore be used as SAs for mode-locking or Q-switching to generate ultrafast fiber laser pulses with a high repetition rate and short duration in the visible, near-infrared, and mid-infrared wavelength regions. Here, we review the recent development of emerging LD nanomaterials as SAs for ultrafast mode-locked fiber laser applications in different dispersion regimes such as anomalous and normal dispersion regimes of the laser cavity operating in the near-infrared region, especially at ~1550 nm. The preparation methods, nonlinear optical properties of LD SAs, and various integration schemes for incorporating LD SAs into fiber laser systems are introduced. In addition to these, externally (electrically or optically) controlled pulsed fiber laser behavior and other characteristics of various LD SAs are summarized. Finally, the perspectives and challenges facing LD SA-based mode-locked ultrafast fiber lasers are highlighted.

Emerging Applications of Elemental 2D Materials

As elemental main group materials (i.e., silicon and germanium) have dominated the field of modern electronics, their monolayer 2D analogues have shown great promise for next-generation electronic materials as well as potential game-changing properties for optoelectronics, energy, and beyond. These atomically thin materials composed of single atomic variants of group III through group VI elements on the periodic table have already demonstrated exciting properties such as near-room-temperature topological insulation in bismuthene, extremely high electron mobilities in phosphorene and silicone, and substantial Li-ion storage capability in borophene. Isolation of these materials within the postgraphene era began with silicene in 2010 and quickly progressed to the experimental identification or theoretical prediction of 15 of the 18 main group elements existing as solids at standard pressure and temperatures. This review first focuses on the significance of defects/functionalization, discussion of different allotropes, and overarching structure-property relationships of 2D main group elemental materials. Then, a complete review of emerging applications in electronics, sensing, spintronics, plasmonics, photodetectors, ultrafast lasers, batteries, supercapacitors, and thermoelectrics is presented by application type, including detailed descriptions of how the material properties may be tailored toward each specific application.

Lead monoxide: a promising two-dimensional layered material for applications in nonlinear photonics in the infrared band

Lead monoxide (PbO), a novel few-layer two-dimensional (2D) material, was theoretically predicted to have an excellent optical response. Herein, the nonlinear optical response of PbO in the infrared region was experimentally investigated. The feasibility of PbO nanosheets as an effective optical saturable absorber was experimentally verified for the first time. Based on the excellent nonlinear optical characteristics, 2D PbO was fabricated as a passive mode locker by depositing onto a fiber patch cord and by decorating on a microfiber, both of which were successfully applied in fiber lasers for the passive mode locking operation. The mode locking pulses of the fiber laser were as short as 650 fs at 1.5 μm. A pulse duration of 5.47 ps with a 1 μm fiber laser was also experimentally verified. Finally, a PbO-decorated microfiber was fabricated as an optical thresholder that can enhance the SNR of a 1 GHz signal up to 6 dB. This finding might facilitate the development of nonlinear photonic devices with high stability and their practical applications in the future.