Broadband Pulsed Fiber Laser Generation with Topological Insulator: Towards the Mid-Infrared Regime

In recent years, topological insulators have aroused the attention of a great number of scientists due to their unique electronic structures and peculiar physical properties. Triggered by the similar electronic structures as graphene, the broadband nonlinear absorption properties of topological insulator were investigated. Moreover, the mode-locked or Q-switched fiber lasers based on topological insulator were realized for broadband operating wavelength. Here, we present an overview of the preparation, transferring, linear and nonlinear optical properties and their applications of topological insulators in pulsed fiber lasers. The pulsed fiber lasers towards mid- infrared regimes have been proposed.

Highly stable femtosecond pulse generation from a MXene Ti_3C_2T_x(T = F, O, or OH) mode-locked fiber laser

Ultrafast fiber lasers are in great demand for various applications, such as optical communication, spectroscopy,biomedical diagnosis, and industrial fabrication. Here, we report the highly stable femtosecond pulse generation from a MXene mode-locked fiber laser. We have prepared the high-quality Ti_3C_2 T_x nanosheets via the etching method, and characterized their ultrafast dynamics and broadband nonlinear optical responses. The obvious intensity-and wavelength-dependent nonlinear responses have been observed and investigated. In addition, a highly stable femtosecond fiber laser with signal-to-noise ratio up to 70.7 dB and central wavelength of 1567.3 nm has been delivered. The study may provide some valuable design guidelines for the development of ultrafast, broadband nonlinear optical modulators, and open new avenues toward advanced photonic devices based on MXenes.

Broadband ultrafast nonlinear optical response of few-layers graphene: toward the mid-infrared regime

Gapless linear energy dispersion of graphene endows it with unique nonlinear optical properties, including broadband nonlinear absorption and giant nonlinear refractive index. Herein, we experimentally observed that fewlayers graphene has obvious nonlinear absorption and large nonlinear refraction, as investigated by the Z-scan technique in the mid-infrared（mid-IR） regime. Our study may not only, for the first time to our knowledge, verify the giant nonlinear refractive index of graphene(～10-7cm2∕W) at the mid-IR, which is 7 orders of magnitude larger than other conventional bulk materials, but also provide some new insights for graphene-based mid-IR photonics,potentially leading to the emergence of several new conceptual mid-IR optoelectronics devices.

Soliton fiber laser mode locked with two types of film-based Bi2Te3 saturable absorbers

We propose a low-threshold soliton fiber laser passively mode locked with two different types of film-like saturable absorbers, one of which is fabricated by mixing Bi2Te3 with de-ionized water, as well as polyvinyl alcohol（PVA）, and then evaporating them in a Petri dish, and the other of which is prepared by directly dropping Bi2Te3 solution on the PVA film. Both Bi2Te3–PVA films exhibit outstanding features of low loss, high flexibility, and easy synthesis. By incorporating Bi2Te3–PVA films into fiber lasers, stable single-soliton emissions are obtained at a low pump power of 13 mW. Our results suggest that the Bi2Te3 can work as a promising mode locker for ultrafast lasers,while PVA is an excellent host for fabricating high-performance film-based saturable absorbers.

Ti2CTx MXene-based all-optical modulator

MXenes,a new class of 2D transition metal carbides,nitrides,and carbonitrides,have attracted much attention due to their outstanding properties.Here,we report the broadband spatial self-phase modulation of Ti2CTx MXene nanosheets dispersed in deionized water in the visible to near-infrared regime,highlighting the broadband nonlinear optical(NLO)response of Ti2CTx MXene.Using ultrafast pulsed laser excitation,the nonlinear refractive index n2 and the thirdorder nonlinear susceptibility χ^(3)monolayer of Ti2CTx MXene were measured to be^10^−13 m^2/W and ~10^−10 esu,respectively.Leveraging the large optical nonlinearity of Ti2CTx MXene,an all-optical modulator in the visible regime was fabricated based on the spatial cross-phase modulation effect.This work suggests that 2D MXenes are ideal broadband NLO materials with excellent prospects in NLO applications.

Ultrafast nonlinear absorption and nonlinear refraction in few-layer oxidized black phosphorus

We experimentally investigated the nonlinear optical response in few-layer oxidized black phosphorus(OBP) by the femtosecond Z-scan measurement technique, and found that OBP not only possesses strong ultrafast saturable absorption but also a nonlinear self-defocusing effect that is absent in black phosphorus(BP). The saturable absorption property originates mainly from the direct band structure, which is still maintained in OBP. The emergence of self-defocusing might originate from the combined consequences of the oxygen-induced defects in BP. Our experimental findings might constitute the first experimental evidence on how to dynamically tune its nonlinear property, offering an inroad in tailoring its optical properties through chemical modification(oxidation, introducing defects, etc.). The versatile ultrafast nonlinear optical properties(saturable absorption and self-defocusing) imply a significant potential of the layered OBP in the development of unprecedented optoelectronic devices, such as mode lockers, optical switches, laser beam shapers, and wavelength converters.

516 mW,nanosecond Nd:LuAG laser Q-switched by gold nanorods

Q-switched operation of an Nd：LuAG laser using gold nanorods（GNRs） as the saturable absorber（SA） is reported, which also produces the highest average power among the nanosecond Nd-doped Q-switched lasers by GNRs-based SA. The applied GNRs are prepared using a seed-mediated growth method and then dropped onto the quartz substrate to fabricate the SA. The average power of the Q-switched laser is 516 mW with the shortest pulse duration of 606.7 ns and the repetition rate of 265.1 kHz.

Graphene/MoS_(2)heterostructure:a robust mid-infrared optical modulator for Er^(3+)-doped ZBLAN fiber laser

We have prepared the graphene∕MoS_(2) heterostructure by a hydrothermal method,and presented its nonlinear absorption parameters and application as a nonlinear optical modulator in the mid-infrared region.Using the nonlinear optical modulator,stable passively Q-switched operation of an Er^(3+)-doped ZrF_(4)-BaF_(2)-LaF_(3)-AlF_(3)-NaF(ZBLAN)fiber laser at~2.8μm can be obtained.The Q-switched Er^(3+)-doped ZBLAN fiber laser can yield per-pulse energy up to 2.2μJ with the corresponding pulse width and pulse repetition rate of 1.9μs and 45 kHz,respectively.Our results indicate that the graphene∕MoS_(2) heterostructure can be a robust optical modulator for pulsed lasers in the mid-infrared spectral range.

Broadband mid-infrared nonlinear optical modulator enabled by gold nanorods:towards the mid-infrared regime

Mid-infrared pulsed lasers operating around the 3 μm wavelength regime are important for a wide range of applications including sensing, spectroscopy, imaging, etc. Despite the recent advances in technology, the lack of a nonlinear optical modulator operating in the mid-infrared regime remains a significant challenge. Here, we report the third-order nonlinear optical response of gold nanorods(GNRs) ranging from 800 nm to the mid-infrared regime(2810 nm) enabled by their size and overlapping behavior-dependent longitudinal surface plasmon resonance. In addition, we demonstrate a wavelength-tunable Er3+-doped fluoride fiber laser modulated by GNRs, which can deliver pulsed laser output, with the pulse duration down to 533 ns, tunable wavelength ranging from 2760.2 to 2810.0 nm, and spectral 3 d B bandwidth of about 1 nm. The experimental results not only validate the GNRs’ robust mid-infrared nonlinear optical response, but also manifest their application potential in high-performance broadband optoelectronic devices.