Feng Zhang

Abstract Studies of the nonlinear optical phenomena that describe the light‐matter interactions in 2D crystalline materials have promoted a diverse range of photonic applications. MXene, as a recently developed new 2D material, has attracted considerable attention because of its graphene‐like but highly tunable and tailorable electronic/optical properties. In this study, we systematically characterize the nonlinear optical response of MXene Ti 3 C 2 T x nanosheets over the spectral range of 800 nm to 1800 nm. A large effective nonlinear absorption coefficient (β eff ∼‐10 −21 m 2 /V 2 ) due to saturable absorption is observed for all of the testing wavelengths. The contribution of saturable absorption is two orders of magnitude higher than other lossy nonlinear absorption processes, and the amplitude of β eff strongly depends on the light bleaching level. A negative nonlinear refractive index (n 2 ∼‐10 −20 m 2 /W) with value comparable to that of the intensively studied graphene was demonstrated for the first time. These results demonstrate the efficient broadband light signal manipulating capabilities of Ti 3 C 2 T x , which is only one member of the large MXene family. The capability of an efficient broadband optical switch is strongly confirmed using Ti 3 C 2 T x as saturable absorbers for mode‐locking operation at 1066 nm and 1555 nm, respectively. A highly stable femtosecond laser with pulse duration as short as 159 fs in the telecommunication window is readily obtained. Considering the diversity of the MXene family, this study may open a new avenue to advanced photonic devices.

Abstract 2D nanomaterials are emerging as a promising platform for ultrashort‐pulse fiber laser technology. This review presents a catalog of the factors affecting the nonlinear optical properties of 2D nanomaterials and the recent progress in processing and integration strategies into saturable absorber devices as versatile, wideband ultrafast optical switches for fiber‐based‐laser short‐pulse generation. Particular focus is on black phosphorus, and a summary of the current status of black‐phosphorus‐based pulsed lasers is given, which provide new potential efficacy for this and other 2D nanomaterials in ultrafast photonic technology.

Abstract Crystalline porous metal–organic frameworks (MOFs) with nanometer‐sized void spaces, large surface areas and ordered reticular motifs have offered a platform for achieving disruptive successes in divisional fields. Great progress in exploring the linear and nonlinear optical features of MOFs has been achieved, yet third‐order optical nonlinearities in two‐dimensional (2D) MOFs have rarely been studied. Here, a broadband nonlinear optical amplitude modification and phase shift are demonstrated in a few‐layer nickel‐ p ‐benzenedicarboxylic acid MOF (Ni‐MOF). The calculated bandgap of Ni‐MOF decreases from 3.12 eV to 0.85 eV as the doping of Ni ions increases, indicating the ability of this material to be used for optical amplitude modulation from the visible to the near‐infrared region, which is experimentally confirmed via a Z‐scan technique. The determined third‐order optical nonlinearities resemble those of other low‐dimensional nonlinear optical materials, suggesting the wide potential of Ni‐MOF for application in optoelectronics. As an example, a Ni‐MOF‐based saturable absorber was implemented into fiber resonators to demonstrate its broadband mode‐locking operations. A femtosecond laser pulse was readily obtained in the telecommunication wavelength window in an integrated all‐fiber resonator. Considering the chemical compatibility and rich variability, these primary investigations pave the way towards advanced photonics based on multifeature MOF materials.

Few-layer bismuthene is an emerging two-dimensional material in the fields of physics, chemistry, and material science. However, its nonlinear optical property and the related photonics device have been seldom studied so far. Here, we demonstrate a sub-200 fs soliton mode-locked erbium-doped fiber laser (EDFL) using a microfiber-based bismuthene saturable absorber for the first time, to the best of our knowledge. The bismuthene nanosheets are synthesized by the sonochemical exfoliation method and transferred onto the taper region of a microfiber by the optical deposition method. Stable soliton pulses centered at 1561 nm with the shortest pulse duration of about 193 fs were obtained. Our findings unambiguously imply that apart from its fantastic electric and thermal properties, few-layer bismuthene may also possess attractive optoelectronic properties for nonlinear photonics, such as mode-lockers, Q-switchers, optical modulators and so on.

Abstract Graphdiyne (GDY), a newly emerging 2D carbon allotrope, has been widely explored in various fields owing to its outstanding electronic properties such as the intrinsic bandgap and high carrier mobility. Herein, GDY‐based photoelectrochemical‐type photodetection is realized by spin‐coating ultrathin GDY nanosheets onto flexible poly(ethylene terephthalate) (PET) substrates. The GDY‐based photodetectors (PDs) demonstrate excellent photo‐responsive behaviors with high photocurrent ( P ph , 5.98 µA cm ‐ 2 ), photoresponsivity ( R ph , 1086.96 µA W ‐ 1 ), detectivity (7.31 × 10 10 Jones), and excellent long‐term stability (more than 1 month). More importantly, the PDs maintain an excellent P ph after 1000 cycles of bending (4.45 µA cm ‐ 2 ) and twisting (3.85 µA cm ‐ 2 ), thanks to the great flexibility of the GDY structure that is compatible with the flexible PET substrate. Density functional theory (DFT) calculations are adopted to explore the electronic characteristics of GDY, which provides evidence for the performance enhancement of GDY in alkaline electrolyte. In this way, the GDY‐based flexible PDs can enrich the fundamental study of GDY and pave the way for the exploration of GDY heterojunction‐based photodetection.