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Abstract
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 absor-ber 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.
... Apart from that, black-phosphorus-analog lead monoxide (PbO) is also of research interest in recent years owing to its excellent photodetection and nonlinear optical properties [15][16][17][18][19][20]. PbO is a layer compound which exists in two crystal forms: red tetragonal (α) and yellow orthorhombic (β) forms [21], both of which have been experimentally synthesized [20,[22][23][24]. ...
... In comparison to the bulk PbO, PbO nanostructures display intriguing properties due to the quantum confinement effect, which makes them hold great promise in the community of optoelectronics/photonics [17][18][19][20][85][86][87]. As we know, the structure-property relationship of nanostructures has a great effect on the practical application. ...
... This phenomenon is in good accordance with the fact that the crystallinity of PbO thin films gradually declines as the concentration of doped Mn increases [89]. munity of optoelectronics/photonics [17][18][19][20][85][86][87]. As we know, the structure-proper relationship of nanostructures has a great effect on the practical application. ...
Black-phosphorus-analog lead monoxide (PbO), as a new emerging 2D material, has rapidly gained popularity in recent years due to its unique optical and electronic properties. Recently, both theoretical prediction and experimental confirmation have revealed that PbO exhibits excellent semiconductor properties, including a tunable bandgap, high carrier mobility, and excellent photoresponse performance, which is undoubtedly of great interest to explore its practical application in a variety of fields, especially in nanophotonics. In this minireview, we firstly summarize the synthesis of PbO nanostructures with different dimensionalities, then highlight the recent progress in the optoelectronics/photonics applications based on PbO nanostructures, and present some personal insights on the current challenges and future opportunities in this research area. It is anticipated that this minireview can pave the way to fundamental research on functional black-phosphorus-analog PbO-nanostructure-based devices to meet the growing demands for next-generation systems.
... 42,54−56 One notable exception has claimed exfoliation of a naturally occurring α-PbO crystal to obtain a few-layer thin pure α-PbO polymorph; however, the source of bulk α-PbO in this study is not clear. 41 Irrespective of the synthesis challenges, these reports demonstrate the potential of 2D PbO in photodetectors, 55 nonlinear infrared optics, 56 gas-sensing, 57 and piezoelectric devices. 54 Figure 1. ...
... PbO is in fact prone to polymorphic transformation, and recent reports on 2D PbO predominantly show a mixture of β and α phases. 55,56,68 However, phase transformation studies on PbO have so far been restricted to the influence of temperature and pressure in bulk systems. 31,67,69 The XRD results, in combination with HRTEM studies, provide further information about the preferred orientation of 2D PbO nanosheets. ...
... The thickest nanosheets obtained at the lowest gforce showed a direct bandgap of 2.8 eV, which corroborates well with the bulk β-PbO. 56,72 The bandgap is observed to consistently increase with the reduction in the nanosheet size, such that the thinnest nanosheets showed a direct bandgap of 3.26 eV. The increase in the bandgap with reduced nanosheet thickness is consistent with prior observations with several other 2D materials and can primarily be attributed to the quantum confinement effects. ...
The emergence of attractive properties in materials at atomically thin regimes has seen an ongoing interest in two-dimensional (2D) materials. An aspect that has lacked focused attention is the effect of 2D material thickness on its crystal structure. As several layered materials naturally exist in mixed metastable phases, it raises an important question of whether a specific polymorph of these mixed-phase materials will be favored at atomically thin limits. This work attempts to address this issue by employing lead monoxide as a model 2D polymorphic system. We propose a reactive oxygen species (ROS) sequestration-mediated liquid-phase exfoliation (LPE) strategy for the facile synthesis of ultrathin PbO. This is followed by a suite of microscopic and spectroscopic analyses of the PbO nanosheets that reveals the polymorphic transformation of orthorhombic (β) PbO to its tetragonal (α) analogue with reduction in nanosheet thickness. The transformation process reveals an interesting crystal structure of ultrathin 2D PbO where [001]-oriented domains of α-PbO coexist alongside [100]-oriented regions of β-PbO. Density functional theory (DFT) calculations support our experimental data by revealing a higher thermodynamic stability of the tetragonal phase in PbO monolayers. These findings are likely to instigate interest in carefully evaluating the crystal structures of ultrathin 2D materials while promoting research in understanding the phase transformation across a range of 2D crystals.
... Recently, PbO has aroused widespread attention due to its applications in battery, 6,7 X-ray imaging detectors, 8 lubricants, 1 rubber sulfuration, 9 and photovoltaics. 10 The nanostructured PbO has exhibited some new properties and better performances than the bulk one. 11 Some wet chemical and physical synthesis strategies have also been developed for various PbO nanostructures, such as nanoparticles (NPs), 12 nanorods, 12,13 nanobelts, 14 and nanoplates or nanosheets. ...
... 11 Some wet chemical and physical synthesis strategies have also been developed for various PbO nanostructures, such as nanoparticles (NPs), 12 nanorods, 12,13 nanobelts, 14 and nanoplates or nanosheets. 4,9 Among them, fabrication of PbO nanosheets has attracted much attention due to their tunable band gap in the visible range, 15 nonlinear optical properties, 10 and high thermodynamic and chemical stability. 16 In addition, such nanosheets could provide the opportunity for surface chemical modification due to the large number of the exposed Pb atoms on them and the relatively weak covalent bond between Pb and O atoms, which induces some specific functions depending on application situations. ...
... 11,17 Conventionally, the syntheses of PbO nanosheets are mainly based on exfoliation methods, including micromechanical, 16 sonochemical, 11 and liquid-phase exfoliation. 10 For instance, Kumar et al. 16 prepared a two-dimensional (2D) α-PbO by micromechanical and sonochemical exfoliation, which exhibits the thickness-dependent fluorescence lifetime. Xing et al. 11 developed a liquid-phase exfoliation route to obtain ultrathin β-PbO nanosheets by placing a mixture of PbO powders and isopropanol on a sonication bath for several hours and demonstrated that the PbO nanosheet-based photodetectors had excellent tunable photoresponse behavior under illumination of ultraviolet−visible lights. ...
Lead oxide (PbO) nanosheets are of significance in design of functional devices. However, facile, green and fast fabrication of ultrathin and homogenous PbO nanosheets with chemically clean surface is still desirable. Herein, a simple and chemically clean route is developed for fabricating such nanosheets via laser ablation of a lead target in water for a short time and then ambient ageing. The obtained PbO nanosheets are (002)-oriented with microsize in planar dimension and ca. 15 nm in thickness. They are mostly hexagonal in shape. Experimental observations of the morphological evolution have revealed that the formation of such PbO nanosheets can be attributed to two processes: (i) laser ablation-induced formation of ultrafine Pb and PbO nanoparticles (NPs); (ii) PbO NPs’ aggregation and their oriented connection growth. Importantly, a composite surface enhanced Raman spectroscopy (SERS) chip is designed and fabricated, by covering a PbO nanosheets’ monolayer on a Au NPs’ film. Such composite SERS chip can be used for the fast and trace detection of gaseous H2S, in which the PbO nanosheets can effectively chemically trap H2S molecules, demonstrating a new application of these PbO nanosheets. The response of this chip to H2S can be detected within 10s and the detection limit is below 1 ppb. Also, this PbO nanosheet-based chip is reusable by heating after use. This study not only deepens understanding the NPs-based formation mechanism of nanosheets, but also provides the renewable SERS-chips for the highly efficient detection of trace gaseous H2S.
... Compared with the bare microfiber, the device has a stronger ability to suppress noise, and the device also has good stability. Using this scheme, all-optical thresholding devices based on microfiber devices modified by other 2D materials have also been reported [176][177][178] (Table 5). ...
With the development of all-optical networks, all-optical devices have become a research hotspot in recent years. Two-dimensional materials, represented by graphene and black phosphorus, have attracted great interest in the scientific community due to their excellent optical, electrical, magnetic, and mechanical properties. Bridging the gap between fiber optics and nanotechnology, microfibers can interact with light and matter at the micro or even nanoscale. By combining two-dimensional materials with microfibers, composite waveguides can be formed. They have the advantages of high nonlinear effect, all-fiber structure, and high damage threshold, etc. The composite waveguide can be directly applied to optical fiber communication systems, and plays an important role in the field of all-optical signal processing with a huge application prospect. In this review, the properties of typical 2D materials are first introduced. Next, the preparation methods of the relevant equipments are introduced and compared. Then, the all-optical signal processing technology based on 2D material-integrated microfiber composite waveguide is reviewed. The latest developments of all-optical modulators, all-optical wavelength converters, all-optical logic gates and all-optical thresholding devices are presented. Finally, the challenges and opportunities for the future development of 2D materials-integrated microfiber optoelectronic devices are summarized.
... In recent years, stochastic and quasi-regular structures based on the close-packed semiconductor nanoparticles, assemblies of nanoparticles with carbon nanofibers, and dielectric, conductive, and semiconducting nanosheet networks have been the object of particular attention as material platforms to be applied in sensorics [1][2][3][4], photonics [5][6][7][8][9], catalytic chemistry [10][11][12], energy storage [13,14], printed electronics [15,16], etc. In addition to various applications, investigation of the characteristics of charge and photon transfer at microscopic, mesoscopic, and macroscopic levels of these systems can contribute to the further development of such fundamental areas of modern science as the percolation theory, physics of complex non-stationary systems, solid state physics, optics of random media, etc. ...
The results of experimental studies of ohmic conductivity degradation in the ensembles of nanostructured anatase bridges under a long-term effect of direct current are presented. Stochastic sets of partially conducting inter-electrode bridges consisting of close-packed anatase nanoparticles were formed by means of the seeding particles from drying aqueous suspensions on the surfaces of silica substrates with interdigital platinum electrodes. Multiple-run experiments conducted at room temperature have shown that ohmic conductivity degradation in these systems is irreversible. It is presumably due to the accumulated capture of conduction electrons by deep traps in anatase nanoparticles. The scaling analysis of voltage drops across the samples at the final stage of degradation gives a critical exponent for ohmic conductivity as ≈1.597. This value satisfactorily agrees with the reported model data for percolation systems. At an early stage of degradation, the spectral density of conduction current fluctuations observed within the frequency range of 0.01–1 Hz decreases approximately as 1/ω, while near the percolation threshold, the decreasing trend changes to ≈1/ω2. This transition is interpreted in terms of the increasing contribution of blockages and subsequent avalanche-like breakdowns of part of the local conduction channels in the bridges into electron transport near the percolation threshold.
... In recent years, dispersed structures based on close-packed semiconductor nanoparticles have been the object of particular attention as material platforms for applications in sensorics [1][2][3][4], photonics [5][6][7][8], catalytic chemistry [9][10][11], etc. In addition to various applications, studies of the features of charge and photon transfer in these systems at microscopic, mesoscopic, and macroscopic levels can contribute to further development of such fundamental areas of modern science as the percolation theory, physics of complex nonstationary systems, solid state physics, optics of random media, etc. ...
The results of experimental studies of ohmic conductivity degradation in the ensembles of nanostructured anatase bridges under long-term effect of direct current are presented. Stochastic sets of interelectrode partially conducting bridges consisting of close-packed anatase nanoparticles were formed by the seeding particles from drying aqueous suspensions on the surfaces of silica substrates with interdigital platinum electrodes. Multiple-run experiments at room temperature have shown that ohmic conductivity degradation in these systems is irreversible. It is presumably due to accumulated capture of conduction electrons by deep traps in anatase nanoparticles. The scaling analysis of voltage drops across the samples at the final stage of degradation gives a critical exponent for ohmic conductivity as 1.597. This value satisfactorily agrees with the reported model data for percolation systems. At an early stage of degradation, the spectral density of conduction current fluctuations wihin the frequency range of 0.01 Hz - 1 Hz decreases approximately as , while near the percolation threshold the decrease trend changes to . This transition is interpreted in terms of an increasing contribution of blockages and subsequent avalanche-like breakdowns of part of the local conduction channels in the bridges into electron transport near the percolation threshold.
... It is a photoactive semiconductor material and an important industrial material which has been used widely as gas sensors, pigments and paints, storage devices, UV blockers and as modifiers in oxide glasses [4][5][6]. Specially, the 2D of PbO recently attracted many attentions due to its excellent nonlinear optical response and light sensitivity in the visible region [7,8]. These materials have two polymorphic, namely a red α-PbO that has a tetragonal structure (litharge) which is stable at low temperature with P4nmm space group and yellow β-PbO that has orthorhombic structure (massicot) stable at high temperature with Pbcm space group [2,3,9]. ...
The β-PbO has low electrical conductivity relative to α-PbO which hinders its application in optoelectronics and other technological devices. The structural, electrical, and optical properties of Co2+, Ni2+, Cu2+, Li+, and Sn2+-doped β-PbO at the Pb site were investigated in this work using Quantum espresso as a DFT tool. The GGA and LDA exchange functionals were used for band structure calculations. The indirect band gap property is indicated by the calculation of electronic band structure, with spin up state band gap values of 2.28 eV, 0.68 eV, 1.01 eV, 1.57 eV, 1.79 eV, and 1.76 eV for pristine, Co2+, Ni2+, Cu2+, Li+, and Sn2+-doped β-PbO, respectively. The spin down states band gap of Co2+ and Ni2+ was 0.1 eV and 0.32 eV, whereas other dopants and pristine β-PbO equal with spin up states. The PDOS calculation shows how each orbital contributes to the formation of deep level valence band, shallow level valence band, and conduction band states. Dopant effects on optical properties such as JDOS, dielectric functions, refractive index, extinction coefficient, reflectivity, absorption coefficient, electron energy loss spectrum, and optical conductivity were thoroughly discussed. This research provides in-depth functional characteristics for guiding laboratory working experiments and the applications of these materials in various fields such as energy storage and solar cells.
... The photon flux density Φ at λ3 = 4.91 μm has reduced to almost zero inside the center region of graphene nanoribbons. The amplitude of electric field |E(λm)| for the m-th GSP mode had a function of r0, Fermi energy Ef, carrier mobility μ and refractive index n1, which can be calculated as |E(λm, r0, Ef, μ, n1)| with FDTD simulation: |E(λm, r0, Ef, μ, n1)| = sqrt(Ex 2 + Ey 2 + Ez 2 ) (12) where r0 is a position in the grapheme region. We concentrated on the property and behavior of collections of photons, which is determined by the nature of graphene surface plasmon wave. ...
We investigate a framework of local field, quality factor and lifetime for tunable graphene nanoribbon plasmonic-photonic absorbers and study the second order and third order nonlinear optical response of surface plasmons. The energy exchange of plasmonic-photonic absorber occurs in two main ways: one way is the decay process of intrinsic loss for each resonant mode and another is the decay process of energy loss between graphene surface plasmon (GSP) mode and the external light field. The quality factor and lifetime of the plasmonic-photonic absorber can be obtained with using the coupled mode theory (CMT) and finite difference time domain (FDTD) method, which are effectively tunable with changing Fermi energy, carrier mobility and superstrate refractive index. The evolutions of total energy and lifetime of GSP are also shown, which are helpful for the study of micro processes in a two-dimensional material plasmonic-photonic absorber. The strongly localized fundamental field induces a desired increase of second harmonic (SH) wave and third harmonic (TH) wave. The manipulation of the quality factor and lifetime of the GSP makes graphene an excellent platform for tunable two-dimensional material plasmonic-photonic devices to realize the active control of the photoelectric/photothermal energy conversion process and higher harmonic generation.
... The former type of SAs, also known as the artificial SA, mainly includes the nonlinear amplifying loop mirror (NALM) [26], the nonlinear optical loop mirror (NOLM) [27] and the nonlinear polarization rotation (NPR) [22,28]. In contrast, the typical real SAs employed in Qswitched and mode-locked fiber lasers mainly include the semiconductor saturable absorber mirrors (SESAMs) [29,30], carbon nanotubes (CNTs) [31][32][33], graphene [34][35][36][37][38] and other noble potential materials [39][40][41][42][43][44][45][46][47][48][49][50]. Significant strides have been achieved in the midinfrared pulse fiber lasers with these various SAs and the continuously updated fiber components, greatly promoting the rapid developments in the pulse laser fields. ...
The mid-infrared fiber lasers in the 2–3.5 μm spectral regions have been extensively applied in many application fields, such as biomedicine, telecommunications, military and nonlinear optics. With the improvements of the fiber components, the pumping regimes and other related technologies, the mid-infrared fiber lasers have made significant progress over the past decades and gradually become comparable with or supersede the traditional lasers in terms of certain lasing performance. In this review, from the beginning with the overview of fiber materials for the mid-infrared regions, we briefly summarize and review the latest research progress of mid-infrared continuous-wave (CW) and short pulse fiber lasers, including Tm³⁺-, Ho³⁺-doped, Tm³⁺-Ho³⁺ co-doped silicate fiber lasers for the 2 μm region and Er³⁺-, Ho³⁺-doped, Ho³⁺-Pr³⁺ co-doped ZBLAN fiber lasers for the 2.8–3.5 μm region. The advances of saturable absorbers applied in the mid-infrared pulse fiber lasers are also explored. Finally, the future prospects and challenges concerning the further development of mid-infrared fiber lasers are discussed and highlighted.
... The NLO response of 2D GeP was characterized by utilizing the OA Z-scan approach with femtosecond pulse sources excited at two different wavelengths (1550 and 1800 nm). Experimental setup is similar to that in the previous reported work [42]. In order to conduct Z-scan measurement, we fabricated the polymer composite film with 2D GeP nanoflakes. ...
Germanium phosphide (GeP), a rising star of novel two-dimensional (2D) material composed of Group IV–V elements, has been extensively studied and applied in photonics thanks to its broadband optical absorption, strong light–matter interaction and flexible bandgap structure. Here, we show the strong nonlinear optical (NLO) properties of 2D GeP nanoflakes in the broadband range with open-aperture Z-scan technique to explore the performance of 2D GeP microfiber photonic devices (GMPDs) in near-infrared (near-IR) and mid-infrared (mid-IR) ultrafast photonics. Our results suggest that employing the GMPD as an optical device in an erbium-doped fiber laser (EDFL) system results in ultrashort pulses and rogue waves (RWs) at 1.55 μm. Likewise, by the incorporation of GMPD into a thulium-doped fiber laser (TDFL) system, stable ultrashort pulse operation is also achieved at 2.0 μm. We expect these findings to be an excellent GMPD that can be applied in mode-locked fiber lasers to open up new avenues for its development and application in ultrafast photonics.
... Owing to its novel physical properties, such as thermal transport, electronic transport, and mechanical properties, research on graphene has developed significantly [2][3][4][5]. Since then, a series of 2D materials have been successively isolated, including topological insulators (TIs) [6][7][8][9][10][11][12], transition metal dichalcogenides (TMDs) [13][14][15][16][17][18][19][20][21], black phosphorus (BP) [22][23][24][25][26][27], MXenes [28], graphitic carbon nitride (g-C 3 N 4 ) [29][30][31], metal-organic frameworks [32][33][34][35][36], GeP [37], lead monoxide [38], tellurium [39,40], selenium [41,42], tin sulfide [43][44][45], tin monosulfide [46], CH 3 NH 3 PbI 3 perovskite [47,48] bismuth quantum dots [49], titanium [50], and the other ones [51,52]. Different from their bulk parental materials, the 2D materials exhibit exotic electronic and optical properties, providing exciting opportunities for nanoscale electronics and photonics. ...
Due to the exotic electronic and optical properties, two-dimensional (2D) materials, such as graphene, topological insulators, transition metal dichalcogenides, black phosphorus, MXenes, graphitic carbon nitride, metal-organic frameworks, and so on, have attracted enormous interest in the scientific communities dealing with electronics and photonics. Combing the 2D materials with the microfiber, the 2D material-decorated microfiber photonic devices could be assembled. They offer the advantages of a high nonlinear effect, all fiber structure, high damage threshold, and so on, which play important roles in fields of pulse shaping and all-optical signal processing. In this review, first, we introduce the fabrication methods of 2D material-decorated microfiber photonic devices. Then the pulse generation and the nonlinear soliton dynamics based on pulse shaping method in fiber lasers and all-optical signal processing based on 2D material-decorated microfiber photonic devices, such as optical modulator and wavelength converter, are summarized, respectively. Finally, the challenges and opportunities in the future development of 2D material-decorated microfiber photonic devices are given. It is believed that 2D material-decorated microfiber photonic devices will develop rapidly and open new opportunities in the related fields.
... The controlled nano-engineering of metal oxides allows the tuning of their dielectric, electronic, and optical properties [12,13]. In addition to their extensive use in gas sensors and energy storage [14,15], metal oxide nanostructures are also excellent candidates for opto-electronic platforms. ...
The electro-optic effect in two-dimensional (2D) MgO nanoflakes synthesized by a microwave-assisted process is demonstrated using a designed optical fiber modulator. The guiding properties of intense core modes excited by the material cavity are modulated by the external electric field. The feasibility of 2D MgO nanoflakes as an effective electro-optic modulator and switching are experimentally verified for the first time, to the best of our knowledge. The proposed optical-fiber-based electro-optic modulator achieves a linear wavelength shift with a high sensitivity of 12.87 pm/V(77.22 nm/kV/mm, in the electric field). The results show that MgO, as a metal oxide 2D material, is a very promising material for electro-optic modulators and switching.
... Up to now, scientists have developed a series of new 2D materials in the laboratory, and some of which are on the large industrial scale. For example, hexagonal boron nitride (h-BN) [28], black phosphorus (BP) [29][30][31][32][33][34][35][36][37][38][39][40][41], metals and their oxides [42][43][44][45][46][47][48][49], layered dihydroxides (LDHs) [50], transition metal dichalcogenides (TMDs) [51][52][53][54][55][56][57][58][59][60][61][62], transition metal carbides/nitrides/ carbonitrides (MXenes) [63][64][65], topological insulator (TI) [66][67][68] have been successfully prepared and characterized. Band gaps of the common 2D materials are distributed in 0-6 eV, including insulators (such as h-BN), semiconductors (such as MoS2, PtSe2, BP, and tellurium [69][70][71] ), semi-metals (such as MoTe2), TI (such as Bi2Se3) and metals (such as 1T-TaS2 [72]). ...
For a long time, human beings have been yearning for free regulation of light waves. But it is limited by poor performances of the natural materials. The emergence of two-dimensional(2D) synthetic nanomaterials greatly promotes the developments of light control technologies, which has dramatically improved the ability of human beings to control light. People can realize flexible regulation of the propagation speed or propagation direction of light wave in material, optical response and frequency, polarization state of light wave based on a series of novel photoelectric properties of 2D synthetic nanomaterials. So, 2D nanomaterials enabled light control technologies have become a research hotspot in recent years. In this review, we summarize the various technologies realized by 2D materials and introduce the related applications. We further analyze, compare these technologies. This review is aimed to give a generalized knowledge of 2D nanomaterials-enabled smart light regulation technologies and their current devices applications, and thus inspiring the exploration and development of other kinds of new light regulation devices and various novel applications. The challenges and the prospects of the future, especially the application of artificial intelligence (AI) in research and development of 2D materials, are also given.
... In the last decade, 2-D nanomaterials, including grapheme, 73,[163][164][165] topological insulators, 53 and transition metal dichalcogenides, [166][167][168] have been widely applied as optical saturable absorbers for MLFLs and have been studied for RW generation. 53 In the last three years, there have been many 2-D materials reported for application in ultrafast fiber lasers, [169][170][171][172] which has significantly enhanced the development of the ultrafast lasers. Continually searching and employing new materials with good saturable absorptions and highly nonlinear characteristics may sufficiently quicken the above-mentioned process. ...
... Subsequently, the MXene-decorated optical device on a microfiber is fabricated using the optical deposition method. 56 Herein, using the mature flame brushing technique, we have drawn the microfiber from a standard single-mode fiber and its diameter is approximately 15 μm. Then, the nonlinear saturable absorption property of the MXene-deposited microfiber device is characterized by balanced twin-power-meter measurement. ...
... So far, among the 2D layered materials, five kinds of hot monoelemental 2D materials, including arsenic (As), antimony (Sb), tellurium (Te), bismuth (Bi) and selenium (Se) (belonging to V A -VI A group), have been successfully synthesized and discovered with various crystal phases [47,48] instead of 2D mental oxide [49] after the discovery of BP. Most importantly, the growth, physics and application of those materials in monolayer or few/multilayered forms are distinctly different from the binary 2DLMs. ...
Two-dimensional (2D) materials have undergone a rapid development toward real applications since the discovery of graphene. At first, graphene is a star material because of the ultrahigh mobility and novel physics, but it always suffered from zero bandgap and limited device application. Then, 2D binary compounds such as transition-metal chalcogenides emerged as complementary materials for graphene due to their sizable bandgap and moderate electrical properties. Recently, research interests have turned to monoelemental and ternary 2D materials. Among them, monoelemental 2D materials such as arsenic (As), antimony (Sb), bismuth (Bi), tellurium (Te), etc., have been the focus. For example, bismuthene can act as a 2D topological insulator with nontrivial topological edge states and high bulk gap, providing the novel platforms to realize the quantum spin-Hall systems. Meanwhile, ternary 2D materials such as Bi 2 O 2 Se, BiOX and CrOX (X=Cl, Br, I) have also emerged as promising candidates in optoelectronics and spintronics due to their extraordinary mobility, favorable band structures and intrinsic ferromagnetism with high Curie temperature. In this review, we will discuss the recent works and future prospects on the emerging monoelemental and ternary materials in terms of their structure, growth, physics and device applications.
... However, the existing 2DM-based SAs also have their own shortcomings. In order to overcome the existing shortcomings of 2DMs and achieve wide applications in industry, some other mono-elemental 2D materials, such as antimonene and bismuthene, have attracted more attention [225][226][227][228][229][230][231][232][233]. In 2017, Song et al. experimentally investigated the broadband non-linear optical response of few-layer antimonene as SA, and obtained ~550-fs pulses in an Erdoped fiber laser [225]. ...
Since graphene was first reported as a saturable absorber to achieve ultrafast pulses in fiber lasers, many other two-dimensional (2D) materials, such as topological insulators, transition metal dichalcogenides, black phosphorus, and MXenes, have been widely investigated in fiber lasers due to their broadband operation, ultrafast recovery time, and controllable modulation depth. Recently, solution-processing methods for the fabrication of 2D materials have attracted considerable interest due to their advantages of low cost, easy fabrication, and scalability. Here, we review the various solution-processed methods for the preparation of different 2D materials. Then, the applications and performance of solution-processing-based 2D materials in fiber lasers are discussed. Finally, a perspective of the solution-processed methods and 2D material-based saturable absorbers are presented.
... But the thermal damage threshold should be improved [23][24][25]. MXene [26], lead monoxide (PbO) [27], metal-organic frameworks [28] and perovskite [29][30][31] have unique physical and chemical properties, are becoming a hotspot. Nevertheless, the nonlinear absorption properties remain to be enhanced. ...
Group IVB (Hf) transition metal dichalcogenides (TMDs) have attracted significant interest in photoelectronics due to their predictable superior physical characteristics. In this work, the liquid phase exfoliation method is used to prepare the hafnium diselenide (HfSe2)/polyvinyl alcohol (PVA) saturable absorber (SA) device. The modulation depth (ΔT) is measured to be 6.65%. By using HfSe2/PVA as a Q-switcher, application in the fiber laser with the Q-switching state is demonstrated experimentally. The maximum single pulse energy is 167 nJ is and the slope efficiency is 7.7%. To our best knowledge, this is the first report of the use of HfSe2 as SA for large energy pulse generation. The experimental results prove that, because of its excellent nonlinear optical absorption properties, HfSe2 could promote the development of Hf-based TMDs in the field of ultrafast photonics.
... In the recent decades, plenty of 2D materials have been discovered and studied [15][16][17]. Various optoelectronics applications of the 2D materials are found, specifically, the 2D material based ultrafast fiber lasers have been intensively investigated, which significantly enhanced the development of nonlinear fiber optics [18][19][20][21][22][23][24][25][26][27]. In 2014, Zhang et al demonstrated a high-performance transistor based on 2D materials, which brings black phosphorus (BP) into our sight [28]. ...
As a unique two-dimensional material, few-layered black phosphorus (BP) nanosheets have shown promising applications in electronics and optoelectronics. Black phosphorus quantum dots (BPQDs) have attracted attention due to the unique properties of BP combined with the edge effects. In this paper, we report on the all optical application of BPQD based on its nonlinear Kerr effect. BPQDs were synthesized using a liquid exfoliation method that combined with probe sonication and bath sonication. BPQD deposited on the microfiber as an optical device was demonstrated as Kerr switcher with extinction ratio of 20 dB and four-wave mixing based wavelength converter with -40 dB conversion efficiency. These findings suggest that BPQD-based novel nonlinear photonics devices could be further developed in the applications of next generation high-speed optical communication.
As a rising star among metal oxide nanomaterials, titanium dioxide (TiO2) has been widely investigated and employed in optical applications because of its excellent optical properties. In this work, we demonstrate the efficient and broadband nonlinear photonic properties of methylene blue (MB)-loaded reduced TiO2 (TiO2−x-MB) and explore the performance of a TiO2−x-MB-microfiber photonic device in broadband ultrafast photonics. Within an erbium-doped fiber laser (EDFL) system, utilizing the TiO2−x-MB-microfiber photonic device as a saturable absorber (SA), steady mode-locked pulses together with chaotic pulses were successfully achieved at the wavelength of 1.55 μm. Furthermore, by incorporating the TiO2−x-MB SA into a thulium-doped fiber laser (TDFL) system, an ultrashort single pulse and multiple pulses were obtained at 2.0 μm. These results indicate that TiO2−x-MB is an excellent nanomaterial for use in mode-locked lasers, being an alternative candidate for ultrafast fiber lasers via exploiting the chemical and physical properties of oxide nanomaterials.
Recent development of pulsed fiber lasers was greatly promoted by their significant applications in various fields. Nanostructured materials show unique physicochemical properties that are different from their bulk counterparts and have attracted much interest due to their promising applications in many areas such as the generation of pulsed fiber lasers. Herein, preparation and pulsed fiber laser applications of emerging nanostructured materials are reviewed. First, preparation methods of the emerging nanostructured materials are summarized. In the following, common characterization techniques of the emerging nanostructured materials are introduced. Then, the state of the art applications of the nanostructured materials as saturable absorbers in pulsed fiber lasers are provided. Finally, a summary and outlook regarding preparation and pulsed fiber laser applications of emerging nanostructured materials are considered.
The black phase of formamidinium lead iodide, FAPbI3, is optically active and promising for optoelectronics applications. However, it is difficult to synthesize and stabilize at room temperature since it thermodynamically tends toward the photoinactive yellow phase. Based on density functional theory computations, the potential of PbO semiconductor substrates to stabilize the black phase of FAPbI3 perovskite is investigated and shown that, interestingly, it can be effectively stabilized over the yellow phase at room temperature when deposited on the polymorphic phase α‐PbO.
Nanomaterials with remarkable optical, mechanical, and electrical properties have shed new light on various fields including optoelectronics, sensors, biomedicine, and ultrafast photonics. Particularly, owing to their nonlinear optical properties, fast recovery time, and broadband operation, nanomaterials are well qualified as saturable absorbers in ultrafast pulsed lasers. Over the development of the past decades, various nanomaterials have been developed as saturable absorbers, which contribute to a diversity of lasers with excellent performance. Therefore, it is important for researchers to provide a landmark of the applications of nanomaterials in ultrafast photonics concerning cutting‐edge development. Herein, the integration and applications of nanomaterials in ultrafast photonics are reviewed. First, end‐face, lateral, as well as photonic crystal fibers padding integration methods are introduced along with their process and characteristics. Then the ultrafast applications of nanomaterials including carbon‐based (carbon nanotubes and graphene), typical 2D (topological insulators, transition metal dichalcogenides, black phosphorus, and MXenes), and metal‐based nanomaterials (gold, silver, copper, and metal oxides) are summarized. Major parameters of ultrafast lasers and features of each nanomaterial are presented simultaneously. Finally, the perspectives of nanomaterials for further development in ultrafast photonics are discussed. Integration methods of coupling nanomaterials to the laser cavities, including end‐face, lateral, and photonic crystal fibers padding integration are described. Then the applications of carbon‐based, typical 2D, and metal‐based nanomaterials in ultrafast pulsed lasers are proposed respectively. Finally, the development trend, potential applications, and challenges of nanomaterials in ultrafast photonics are prospected.
In recent years, 2D oxides have attracted considerable attention due to their novel physical properties and excellent stability. With the efforts of researchers, significant progress has been made in the synthesis and electronics and optoelectronics application of 2D oxides. Herein, a systematic review focusing on the preparation of 2D oxides and their applications in electronics and optoelectronics is provided. First, 2D oxides are summarized and classified according to their elements. Then, common preparation methods to synthesize 2D oxides including exfoliation, liquid‐phase synthesis, vapor deposition, surface oxidation of metal, and so on are introduced. Further, the applications of 2D oxides in electronics and optoelectronics are presented. Finally, the current challenges and envisioned development of 2D oxides are commented and prospected. Due to the excellent properties and air stability, 2D oxides show promising application prospects in optoelectronics and electronics, which are expected to promote the development of the semiconductor industry together with common other 2D materials. Herein, the preparation and application in optoelectronics and electronics of 2D oxides in recent years are summarized.
Since the advent of graphene, two-dimensional materials with various novel properties have received more and more attention in the fields of optoelectronic devices, spintronics and valley electronic devices. Among them, the excellent properties that appear in graphene with various molecular groups for asymmetric functionalization have led to the research of other Janus two-dimensional materials with asymmetric surface characteristics. As an important derivative of two-dimensional materials, Janus two-dimensional materials (especially Janus transition metal chalcogenides) have become a research hotspot in recent years. Both experiment and theory have confirmed that this kind of material has mirror asymmetry and novel characteristics, such as strong Rashba effect and out-of-plane piezoelectric polarization, and thus showing a great prospect for its applications in sensors, actuators, and other electromechanical devices. In this review we introduce the recent research progress of emerging Janus two-dimensional materials (including Janus graphene, various Janus two-dimensional materials and Janus two-dimensional van der Waals heterojunction), and summarize the unique electronic properties and potential applications of Janus two-dimensional materials. Finally, we draw some conclusions and depict a prospect of further exploration of Janus two-dimensional materials.
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 (TMCs), Topological Insulators (TIs) and Black Phosphorus (BP) 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.
Nanomaterials have demonstrated excellent mechanical, thermal, optical, and electrical properties in various fields, including 1D carbon nanotubes, as well as 2D materials starting from graphene. Metal‐based nanomaterials, mainly divided into metal and metal oxide nanoparticles, also gradually come into the sight of ultrafast photonics applications due to the outstanding optical properties. The optical properties of metal nanoparticles can be enhanced by the interaction between conduction electrons with electric fields that is called surface plasmon resonance. As for metal oxide nanoparticles, optical properties are closely related to bandgap structures. When it comes to transition metal oxides, other phenomena also play important roles in optical absorption such as spin inversion and excitons of iron. Moreover, preparation methods of materials are also crucial for their properties and further applications. Therefore, in this review, commonly used physical and chemical fabrication methods for metal‐based nanomaterials are first introduced. Then the optical properties of typical metal and metal oxide nanoparticles are discussed specifically. In addition, the applications of metal‐based nanomaterials in ultrafast lasers based on mode‐locked and Q‐switched techniques are also summarized. Finally, a summary and outlook toward the synthesis, optical properties, and applications in ultrafast photonics of metal‐based nanomaterials are presented. Metal‐based nanomaterials gradually come into the sight of ultrafast photonics due to the outstanding optical properties. The state of the art of metal‐based nanomaterials in fabrications, optical properties, and applications as saturable absorbers are summarized in this review, aiming to accelerate the exploration of nanomaterials and further stimulate the applications in various fields.
Study of nonlinear laser-matter interactions in 2D materials has promoted development of photonics applications. As a typical MXene material, molybdenum carbide (Mo2C) has attracted much attention because of its graphene-like structure. Here, a type of D-shaped fiber (DF)-buried Mo2C saturable absorber (SA) fabricated by magnetron-sputtering deposition (MSD) and sol-gel technique is reported. The Mo2C material was buried between the bottom DF and the upper amorphous silica fabricated by sol-gel technology. Therefore, the DF-based SA effectively solves the problem of material shedding and aging, thus improving the stability and damage threshold of the fiber laser. Application of the SA in erbium-doped fiber laser and stable passive Q-switched operation with a maximum pulse energy of 430.47 nJ is realized. By adjusting the polarization state and pump power, high-power mode-locked pulses are generated with a pulse duration and output power of 199 fs and 54.13 mW, respectively. Further, bound-state soliton pulses are obtained with a pulse width of 312 fs and soliton interval of 1.26 ps for the first time based on MXene materials. Moreover, by application of the SA in ytterbium-doped fiber lasers, a stable dissipative soliton mode-locked pulse is obtained with a pulse width of 23 ps. These results indicate that the DF-based buried Mo2C as a novel SA provides a reliable method for all-fiber and multifunctional high-power ultrafast laser.
Tellurene, as a typical non-layered two-dimensional (2D) material, has attracted a lot of attention due to its superior properties such as fast photoconductivity, high thermoelectricity, large piezoelectricity, and excellent nonlinear optical response. Here, a unique, simple, and rapid solution method for the synthesis of high-quality hexagonal Te nanosheets with large area has been proposed. In the presence of polyvinylpyrrolidone (PVP) as a surfactant, the raw material, i.e., tellurium sodium hydride (NaHTe) was rapidly oxidized by O2 in ethanol solution to obtain the hexagonal Te nanosheets with a size of 5–11 μm and a thickness of 50–170 nm. In addition, the experimental results demonstrated that the prepared hexagonal Te nanosheets possessed good optical absorption and exhibited good photoresponse and stability as a photoanode material in a photoelectrochemical (PEC)-type photodetector. Meanwhile, this material also showed excellent nonlinear absorption properties, and the erbium-doped fiber ring laser with the Te nanosheets as a saturated absorption material successfully achieved mode-locking operation at 1550 nm. This work provides new ideas for the preparation of hexagonal Te nanosheets and their applications in optoelectronics and ultrafast photonics.
The innovation of the graphene (G) has motivated a huge attention for the study of the other novel two dimensional materials (2DMs), known as modern day ‘‘alchemy”, by which scientists are trying to convert most of possible periodic table elements into the 2DMs structures. Among the 2DMs family, the newly invented monoelemental, atomically thin 2DMs of the group IIIA-VIA, called “Xenes" (where, X = IIIA-VIA groups elements, and "ene" Latin word mean nanosheets (NSs)), are very active area of research for the future nanodevices fabrications with high speed, low cost and elevated efficient. Any new form of the 2DMs enters into mainstream Xenes would likely compete with today's electronic technology. Modern highly sensitive potential synthesis and characterization techniques offer an opportunity for investigating theoretically predicted 2D-Xenes with atomic precision in idealize circumstances, so, providing theoretical predictions experimental support. Experimental based theoretically predicted number of synthetic 2D-Xenes material have been investigated in the group-VIA elements (Tellurene (2D-Te), and Selenene (2D-Se)) are like topological insulators (TIs), thus potentially rendering them as a suitable candidates for the future nanodevices. Although these materials investigation and devices application are still at an early stage, but the theoretical calculations and some experimental measurements, proved that they are complementary to the conventional (i.e., layered bulk-derived) 2DMs. This review will concentrate on the synthesis of the novel group-VIA Xenes (2D-Te and 2D-Se) and will summarize the recent progress in understanding their basic properties, with the current advancement in the signifying devices applications. Finally, the prospects for the future research, their further advanced application prospects and the associated challenges of the group-VIA Xenes will also be summarized and highlighted.
The mitigation of the health hazards and environmental pollution by Pb is necessary. However, piezoelectric Pb containing compounds, such as PZT, are still widely used in many industries and health sectors. One approach to reduce the hazards and contaminations by Pb is to decrease the amount of this element in the devices by size reduction. In this regard, the possibility of using ultra-thin piezoelectric PbO films should be investigated. However to date, the development of such two dimensional (2D) PbO films, in large lateral dimensions, has faced certain challenges. Here a liquid metal-based 2D printing technique is employed to produce unit-cell thick PbO sheets by harvesting the interfacial oxide layer of liquid Pb. The resulted PbO monolayer, of hundreds of micron lateral dimensions, exhibits an orthorhombic crystal phase with a wide direct band gap of 3.3 eV, larger than that of its bulk value. In addition, remarkable vertical piezoelectric coefficients of ~30 pm V-1 was determined in unit-cell thick PbO through both measurements and density functional theory calculations. The PbO monolayers can be employed as the environmentally friendly alternative of PZT, in many commercial applications, due to the small content of Pb.
The plasmonic response of lead films deposited on nanostructured substrates formed by nanoconcave and nanodome arrays through optical reflectance spectroscopy measurements in the 190–1400 nm wavelength range was investigated. We found that their optical reflectance can be modified by changing the dimensions of the nanostructured substrates in a manner that the observed minima can be varied in the 570–1300 nm wavelength range, which were ascribed to plasmonic resonances. Also, a comparison with aluminum and silver, two metals commonly used in plasmonics, was made showing that lead can be used as an alternative plasmonic material within the Vis-IR range of the electromagnetic spectrum.
Tin selenide (SnSe) nanosheets, as 2D materials, exhibit many excellent optical and electronic properties and can be widely utilized in various potential applications, such as photodetectors, photovoltaic cells, optical sensors, and nonlinear optical devices. Herein, the 2D SnSe nanosheets are synthesized by the method combining lithium ion intercalation and sonication‐assisted liquid phase exfoliation. The morphology, structures, and chemical composition of as‐prepared 2D SnSe sample are systemically analyzed. Interestingly, the 2D SnSe nanosheets are successfully fabricated as a saturable absorber (SA) by depositing on a microfiber, which shows excellent nonlinear absorption property in a wide band. By incorporating SnSe‐based SA into the fiber lasers, stable mode‐locked pulses can be realized at 1.5 and 2 µm with a pulse duration of 0.542 and 2.12 ps, respectively. Additionally, harmonic mode locking of bound solitons is generated in the 1.5 µm fiber laser. Furthermore, dual‐wavelength mode‐locked pulses at 1897.3 and 1910.5 nm are also obtained in the 2 µm fiber laser. These results validate that 2D SnSe materials show great potential in nonlinear photonic devices for broadband ultrafast photonics.
Based on the extensive investigation on graphene and graphene derivatives asymmetrically functionalized by a variety of molecular groups, and the concept of Janus materials with asymmetric facial properties, Janus two-dimensional (2D) materials as a derivative of 2D material family, including Janus graphene and Janus transition metal chalcogenides etc, have attracted much attention in recent years. Janus 2D materials have been demonstrated experimentally and theoretically to possess unique properties such as the out-of-plane piezoelectric polarization and strong Rashba effect due to their out-of-plane asymmetry. Here, the recent progresses of emerging Janus 2D materials, including Janus graphene, prediction and fabrication of various different Janus 2D materials and Janus 2D van der Waals heterostructures, are presented. The investigations on the unique properties and potential device applications of Janus 2D materials are summarized. Finally, the conclusion and prospects for the future explorations on Janus 2D materials are also suggested.
We report the generation of 240 nJ, robust pulses at 1.5 μm by inserting the hafnium sulfide (HfS2) into the compact Er-doped fiber (EDF) laser. The multilayer HfS2 nanosheets prepared by liquid exfoliation was experimentally studied as a good performance saturable absorber (SA) with the modulation depth (ΔT) of 11.32%. The slope efficiency of fiber laser is as high as 8.9%. Compared with recent reported works, our experimental results show better comprehensive performance. This work demonstrates that HfS2 with prominent nonlinear saturable absorption property could be used as a promising candidate to advance the development of nonlinear optics.
Two-dimensional (2D) ferromagnetism is critical for both scientific investigation and technological development owing to its low-dimensionality that brings in quantization of electronic states as well as free axes for device modulation. However, the scarcity of high-temperature 2D ferromagnets has been the obstacle of many research studies, such as the quantum anomalous Hall effect (QAHE) and thin-film spintronics. Indeed, in the case of the isotropic Heisenberg model with finite-range exchange interactions as an example, low-dimensionality is shown to be contraindicated with ferromagnetism. However, the advantages of low-dimensionality for micro-scale patterning could enhance the Curie temperature (TC) of 2D ferromagnets beyond the TC of bulk materials, opening the door for designing high-temperature ferromagnets in the 2D limit. In this paper, we review the recent advances in the field of 2D ferromagnets, including their material systems, physical properties, and potential device applications.
In recent years, layered black phosphorus (BP) nanostructures demonstrated great potential applications in transistors, optoelectronics and logic devices due to their excellent intrinsic electronic and optoelectronic properties. However, the high cost of BP and its rapid degradation upon exposure to ambient conditions turn out to be the two critical bottlenecks hampering practical applications. With the developments of semiconductors in leaps and bounds, a new wave of exploration of black phosphorus analogues (BPAs), whose excellent optoelectronic performance and high chemical stability under ambient conditions unveil great promises for practical applications, has emerged. This review presents the synthesis and morphology control of emerging BPAs, the latest progress in understanding the fundamental properties of BPA nanostructures, and the recent advances in constructing prototypical high-performance BPA-based devices for practical applications. Finally, the prospects for future research, application opportunities, and the accompanying challenges of BPAs are discussed.
Bismuthene, as a new two-dimensional (2D) material made up of diazo metal elements, has drawn massive attention for its unique electronic, mechanical, quantum, and nonlinear optical properties. In recent years, researchers have increasingly turned their attention to the ultrafast photonics fields based on bismuthene. However, the internal ultrashort pulse dynamics has seldom been explored yet. In this work, the nonlinear optical properties of bismuthene nanosheets have been studied and applied in a passively mode-locked fiber laser. The saturation intensity and modulation depth of SA device are about 2.4 MW/cm2 and 1%, respectively. Thanks to the narrow bandgap of bismuthene and tapered fiber structure, a special kind of noise-like multipulses have been obtained. The evolution of the pulsed laser is also studied. This proposed pulsed fiber laser based on bismuthene SA device is well suitable for some applications such as material processing, optical logics etc.
With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber lasers at 3.5 μm have become a fascinating area of research. However, limited by the absence of suitable saturable absorber, passively Q-switched and mode-locked fiber lasers have not been realized in this spectral region. Based on the layer-dependent bandgap and excellent photoelectric characteristics of black phosphorus (BP), BP is a promising candidate for saturable absorber near 3.5 μm. Here, we fabricated a 3.5-μm saturable absorber mirror (SAM) by transferring BP flakes onto a Au-coated mirror. With the as-prepared BP SAM, we realized Q-switching and mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 μm. To the best of our knowledge, it is the first time to achieve passively Q-switched and mode-locked pulses in 3.5 μm spectral region. The research results will not only promote the development of 3.5-μm pulsed fiber lasers but also open the photonics application of two-dimensional materials in this spectral region.
Black phosphorus (BP) has attracted growing attentions due to its unique electrical properties. In addition, the outstanding optical nonlinearity of BP has been demonstrated in various ways. Its functionality as a saturable absorber especially has been validated in demonstrations of passive mode-locked lasers. However, normally, the performance of BP is degraded eventually by both thermal and chemical damage in ambient condition. Passivation of BP is the critical issue to guarantee a stable performance of the optical devices. We characterized the mode-locked lasers operated by BP saturable absorbers with diversified passivation materials such as polydimethylsiloxane (PDMS) or Al2O3 considering atomic structure of the materials, therefore hydro-permeability of the passivation layers. Unlike the BP layers without passivation, we demonstrated that the Al2O3-passivated BP layer was protected from the surface oxidation reaction in long-term scale, and PDMS-passivated one had a short-term blocking effect. Quantitative analysis showed that the time-dependent characteristics of pulsed laser without passivation were changed in the pulse duration, spectral width, and time-bandwidth product displaying 550 fs, 2.8 nm, and 0.406, respectively. With passivation, the changes were limited to < 43 fs, < 0.3 nm, and < 0.012, respectively.
Antimonene, a new type of mono/few-layer two-dimensional (2D) mono-elemental material purely consisting of antimony similar as graphene and phosphorene, has been theoretically predicted with excellent optical response and enhanced stability. Herein, we experimentally investigated the broadband nonlinear optical response of highly stable few-layer antimonene (FLA) by performing an open-aperture Z-scan laser measurement. Thanks to the direct bandgap and resonant absorption at the telecommunication band, we demonstrated the feasibility of FLA-decorated microfiber not only as an optical saturable absorber for ultrafast photonics operation, but also as a stable all-optical pulse thresholder that can effectively suppress the transmission noise, boost the signal-to-noise ratio (SNR), and reshape the deteriorated input signal. Our findings, as the first prototypic device of absorption of antimonene, might facilitate the development of antimonene-based optical communication technologies towards high stability and practical applications in the future.
2D transition metal carbides, nitrides, and carbonitides called MXenes have attracted much attention due to their outstanding properties. However, MXene's potential in laser technology is not explored. It is demonstrated here that Ti3 CN, one of MXene compounds, can serve as an excellent mode-locker that can produce femtosecond laser pulses from fiber cavities. Stable laser pulses with a duration as short as 660 fs are readily obtained at a repetition rate of 15.4 MHz and a wavelength of 1557 nm. Density functional theory calculations show that Ti3 CN is metallic, in contrast to other 2D saturable absorber materials reported so far to be operative for mode-locking. 2D structural and electronic characteristics are well conserved in their stacked form, possibly due to the unique interlayer coupling formed by MXene surface termination groups. Noticeably, the calculations suggest a promise of MXenes in broadband saturable absorber applications due to metallic characteristics, which agrees well with the experiments of passively Q-switched lasers using Ti3 CN at wavelengths of 1558 and 1875 nm. This study provides a valuable strategy and intuition for the development of nanomaterial-based saturable absorbers opening new avenues toward advanced photonic devices based on MXenes.
Phosphorene, mono/few-layered black phosphorous with advantages of tunable energy bandgaps and strong light–matter interaction, is fabricated by electrochemical intercalation with large area (≈3 µm) and controllable thickness (mainly four layers). Thanks to the direct gap and resonant absorption of four-layer phosphorene at the telecommunication band, all-optical thresholding and optical modulation are demonstrated for optical communications by using few-layer phosphorene-decorated microfibers. This device is experimentally verified as an efficient noise suppressor that can enhance the signal-to-noise ratio and reshape the deteriorated signal pulse, and also as an optical modulator that can switch the signal on/off by pumping light. The findings, as the first prototypic device of all-optical thresholding and optical modulation, might facilitate the development of phosphorene-based optical communication technologies.
We experimentally demonstrate a practical and simple method for the preparation of a graphite-based, fiberized saturable absorber (SA). Our SA is prepared by using a low-cost graphite-core pencil that is commercially available from stationary stores to uniformly shade the flat end of a fiber ferrule. The saturable-absorption performance of the prepared SA was experimentally tested, and the feasibility of using the SA as a passive Q -switch was investigated through its incorporation into an erbium-doped-fiber ring cavity. The modulation depth of the SA is ∼ 1 % , and the Q -switched pulses of a 1.98 μs temporal width were readily obtained at a repetition rate of 46.08 kHz.
Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two-dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm(2) V(-1) s(-1) . Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics.
We report, for the first time to our knowledge, the usage of black phosphorus (BP) as a saturable absorber for the mode locking of a thulium-doped fiber laser. We have experimentally shown that BP exhibits saturable absorption in the 2 μm wavelength range and supports ultrashort pulse generation. The saturable absorber was based on mechanically exfoliated BP deposited on a fiber connector tip. The laser was capable of generating 739 fs pulses centered at 1910 nm. Our results show that BP might be considered as a universal broadband saturable absorber that could successfully compete with graphene or other low-dimension nanomaterials.
Black phosphorus (BP), an emerging narrow direct band-gap two-dimensional (2D) layered material that can fill the gap between the semi-metallic graphene and the wide-bandgap transition metal dichalcogenides (TMDs), had been experimentally found to exhibit the saturation of optical absorption if under strong light illumination. By taking advantage of this saturable absorption property, we could fabricate a new type of optical saturable absorber (SA) based on mechanically exfoliated BPs, and further demonstrate the applications for ultra-fast laser photonics. Based on the balanced synchronous twin-detector measurement method, we have characterized the saturable absorption property of the fabricated BP-SAs at the telecommunication band. By incorporating the BP-based SAs device into the all-fiber Erbium-doped fiber laser cavities, we are able to obtain either the passive Q-switching (with maximum pulse energy of 94.3 nJ) or the passive mode-locking operation (with pulse duration down to 946 fs). Our results show that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.
Few-layer black phosphorus (BP), as the most alluring graphene analogue owing to its similar structure as graphene and thickness dependent direct band-gap, has now triggered a new wave of research on two-dimensional (2D) materials based photonics and optoelectronics. However, a major obstacle of practical applications for few-layer BPs comes from their instabilities of laser-induced optical damage. Herein, we demonstrate that, few-layer BPs, which was fabricated through the liquid exfoliation approach, can be developed as a new and practical saturable absorber (SA) by depositing few-layer BPs with microfiber. The saturable absorption property of few-layer BPs had been verified through an open-aperture z-scan measurement at the telecommunication band. The microfiber-based BP device had been found to show a saturable average power of ~4.5 mW and a modulation depth of 10.9%, which is further confirmed through a balanced twin detection measurement. By integrating this optical SA device into an erbium-doped fiber laser, it was found that it can deliver the mode-locked pulse with duration down to 940 fs with central wavelength tunable from 1532 nm to 1570 nm. The prevention of BP from oxidation through the “lateral interaction scheme” owing to this microfiber-based few-layer BP SA device might partially mitigate the optical damage problem of BP. Our results not only demonstrate that black phosphorus might be another promising SA material for ultrafast photonics, but also provide a practical solution to solve the optical damage problem of black phosphorus by assembling with waveguide structures such as microfiber.
As the only non-carbon elemental layered allotrope, few-layer black
phosphorus or phosphorene has emerged as a novel two-dimensional (2D)
semiconductor with both high bulk mobility and a band gap. Here we report
fabrication and transport measurements of phosphorene-hexagonal BN (hBN)
heterostructures with one-dimensional (1D) edge contacts. These transistors are
stable in ambient conditions for >300 hours, and display ambipolar behavior, a
gate-dependent metal-insulator transition, and mobility up to 4000 $cm^2$/Vs.
At low temperatures, we observe gate-tunable Shubnikov de Haas (SdH)
magneto-oscillations and Zeeman splitting in magnetic field with an estimated
g-factor ~2. The cyclotron mass of few-layer phosphorene holes is determined to
increase from 0.25 to 0.31 $m_e$ as the Fermi level moves towards the valence
band edge. Our results underscore the potential of few-layer phosphorene (FLP)
as both a platform for novel 2D physics and an electronic material for
semiconductor applications.
We study the environmental instability of mechanically exfoliated few-layer
black phosphorus (BP). From continuous measurements of flake topography over
several days, we observe an increase of over 200% in volume due to the condensation
of moisture from air. We find that long term exposure to ambient conditions results
in a layer-by-layer etching process of BP flakes. Interestingly, flakes can be etched
down to single layer (phosphorene) thicknesses. BP’s strong affinity for water greatly
modifies the performance of fabricated field-effect transistors (FETs) measured in
ambient conditions. Upon exposure to air, we differentiate between two timescales
for changes in BP FET transfer characteristics: a short timescale (minutes) in which
a shift in the threshold voltage occurs due to physisorbed oxygen and nitrogen, and a
long timescale (hours) in which strong p-type doping occurs from water absorption.
Continuous measurements of BP FETs in air reveal eventual degradation and breakdown
of the channel material after several days due to the layer-by-layer etching
process.
Two-dimensional crystals are emerging materials for nanoelectronics. Development of the field requires candidate systems with both a high carrier mobility and, in contrast to graphene, a sufficiently large electronic bandgap. Here we present a detailed theoretical investigation of the atomic and electronic structure of few-layer black phosphorus (BP) to predict its electrical and optical properties. This system has a direct bandgap, tunable from 1.51 eV for a monolayer to 0.59 eV for a five-layer sample. We predict that the mobilities are hole-dominated, rather high and highly anisotropic. The monolayer is exceptional in having an extremely high hole mobility (of order 10,000 cm(2) V(-1) s(-1)) and anomalous elastic properties which reverse the anisotropy. Light absorption spectra indicate linear dichroism between perpendicular in-plane directions, which allows optical determination of the crystalline orientation and optical activation of the anisotropic transport properties. These results make few-layer BP a promising candidate for future electronics.
The nonlinear optical property of few-layered MoS2 nanoplatelets synthesized by the hydrothermal exfoliation method was investigated from the visible to the near-infrared band using lasers. Both open-aperture Z-scan and balanced-detector measurement techniques were used to demonstrate the broadband saturable absorption property of few-layered MoS2. To explore its potential applications in ultrafast photonics, we fabricated a passive mode locker for ytterbium-doped fibre laser by depositing few-layered MoS2 onto the end facet of optical fiber by means of an optical trapping approach. Our laser experiment shows that few-layer MoS2-based mode locker allows for the generation of stable mode-locked laser pulse, centered at 1054.3 nm, with a 3-dB spectral bandwidth of 2.7 nm and a pulse duration of 800 ps. Our finding suggests that few-layered MoS2 nanoplatelets can be useful nonlinear optical material for laser photonics devices, such as passive laser mode locker, Q-switcher, optical limiter, optical switcher and so on.
Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.
We report on the generation of passive harmonic mode locking of a fiber laser using a microfiber-based topological insulator (TI) Bi 2 Te 3 saturable absorber (SA). The optical deposition method was employed to fabricate the microfiber-based TISA. By virtue of the excellent nonlinear optical property of the proposed TISA, the fiber laser could operate at the pulse repetition rate of 2.04 GHz under a pump power of 126 mW, corresponding to the 418th harmonic of fundamental repetition frequency. The results demonstrate that the microfiber-based TI photonic device can operate as both the high nonlinear optical component and the SA in fiber lasers, and could also find other applications in the related fields of photonics.
Passive Q-switching was experimentally demonstrated in an erbium-doped fiber laser (EDFL) by using gold nanocrystals (GNCs). The GNCs were mixed with sodium carboxymethylcellulose (NaCMC) to form GNCs-NaCMC films. The films exhibited a broad absorption band in the range of 400–1750 nm. By placing the GNCs-NaCMC film in an EDFL cavity pumped by a 980 nm laser diode, stable passive Q-switching was achieved for a threshold pump power of ∼30 mW, and 3.2 μs pulses at 1560 nm with a repetition rate of 24.2 kHz were obtained for a pump power of ∼125 mW.
An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated. It showed that the higher-order soliton compression effect caused by the combination of anomalous dispersion and Kerr nonlinearity can provide incorrect pulse-width information. Third, an experimental investigation into the precise role of the graphene oxide-deposited side-polished fiber was carried out to determine whether its polarization-dependent loss (PDL) can be a substantial contributor to mode-locking through nonlinear polarization rotation. By comparing its performance with that of a gold-deposited side-polished fiber, the PDL contribution to mode-locking was found to be insignificant, and the dominant mode-locking mechanism was shown to be saturable absorption due to mutual interaction between the evanescent field of the oscillated beam and the deposited graphene oxide particles.
The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created
a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for
a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures
to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities
in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption
and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely
efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum
efficiency of above 30%).
We experimentally investigated the vector multi-soliton operation and vector soliton interaction in an erbium doped fiber laser passively mode locked by atomic layer graphene. It is found that the vector multi-soliton operation exhibited several characteristic modes. These are the random static distribution of vector solitons, stable bunches of vector solitons, restless oscillations of vector solitons, rain of vector solitons, and emission of a so-called “giant vector soliton”. The formation mechanisms of the operation modes were also experimentally investigated.
Graphene with zero-band gap can be easily saturated under strong
excitation due to Pauli blocking. In this work, the graphene oxide membrane
is reduced on the surface of microfiber by use of high temperature heating.
Such reduced graphene oxide can interact with the strong evanescent field of
the microfiber and enable saturable absorption in passively mode-locked
fiber laser. The system can be effectively utilized to directly generate
ultra-wide-band doublet pulses for high-capacity wireless communication
applications.
The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.
We demonstrate a nanosecond-pulse erbium-doped fiber laser that is passively mode locked by a hollow-core photonic crystal fiber filled with few-layered graphene oxide solution. Owing to the good solution processing capability of few-layered graphene oxide, which can be filled into the core of a hollow-core photonic crystal fiber through a selective hole filling process, a graphene saturable absorber can be successfully fabricated. The output pulses obtained have a center wavelength, pulse width, and repetition rate of 1561.2 nm, 4.85 ns, and 7.68 MHz, respectively. This method provides a simple and efficient approach to integrate the graphene into the optical fiber system.
If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties
would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, and Bi2Te3 can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron
microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions
of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films.
We show that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.
The electronic properties of ultrathin crystals of molybdenum disulfide
consisting of N = 1, 2, ... 6 S-Mo-S monolayers have been investigated by
optical spectroscopy. Through characterization by absorption,
photoluminescence, and photoconductivity spectroscopy, we trace the effect of
quantum confinement on the material's electronic structure. With decreasing
thickness, the indirect band gap, which lies below the direct gap in the bulk
material, shifts upwards in energy by more than 0.6 eV. This leads to a
crossover to a direct-gap material in the limit of the single monolayer. Unlike
the bulk material, the MoS2 monolayer emits light strongly. The freestanding
monolayer exhibits an increase in luminescence quantum efficiency by more than
a factor of 1000 compared with the bulk material.
Pulses as short as 260 fs have been generated in a diode-pumped low-gain
Er:Yb:glass laser by exploiting the nonlinear optical response of single-layer
graphene. The application of this novel material to solid-state bulk lasers
opens up a way to compact and robust lasers with ultrahigh repetition rates.
The richness of optical and electronic properties of graphene attracts
enormous interest. Graphene has high mobility and optical transparency, in
addition to flexibility, robustness and environmental stability. So far, the
main focus has been on fundamental physics and electronic devices. However, we
believe its true potential to be in photonics and optoelectronics, where the
combination of its unique optical and electronic properties can be fully
exploited, even in the absence of a bandgap, and the linear dispersion of the
Dirac electrons enables ultra-wide-band tunability. The rise of graphene in
photonics and optoelectronics is shown by several recent results, ranging from
solar cells and light emitting devices, to touch screens, photodetectors and
ultrafast lasers. Here we review the state of the art in this emerging field.
We report results of numerical simulations on the multiple soliton generation and soliton energy quantization in a soliton fiber ring laser passively mode-locked by using the nonlinear polarization rotation technique. We found numerically that the formation of multiple solitons in the laser is caused by a peak power limiting effect of the laser cavity. It is also the same effect that suppresses the soliton pulse collapse, an intrinsic feature of solitons propagating in the gain media, and makes the solitons stable in the laser. Furthermore, we show that the soliton energy quantization observed in the lasers is a natural consequence of the gain competition between the multiple solitons. Enlightened by the numerical result we speculate that the multi-soliton formation and soliton energy quantization observed in other types of soliton fiber lasers could have similar mechanism.
An optical thresholding technique based on super-continuum generation in dispersion flattened fiber is proposed and experimentally demonstrated to enable data-rate detection in optical code division multiple access networks. The proposed scheme exhibits an excellent discrimination between a desired signal and interference signals with features of pulse reshaping, low insertion loss, polarization independency as well as reasonable operation power.
A nonphotocatalytic reaction occurring on the surface of an irradiated wide band gap metal oxide, such as ZrO2, can affect the process of photoinduced formation of Zr3+, F- and V-type color centers. The effect of such reactions is seen as the influence of photostimulated adsorption on the photocoloration of the metal oxide specimen. In particular, photoadsorption of electron donor molecules leads to an increase of electron color centers, whereas photoadsorption of electron acceptor molecules leads to an increase of hole color centers. Monitoring the photocoloration of a metal oxide during a surface photochemical reaction probes whether the reaction is photocatalytic: accordingly, the influence of simple photoreactions on the photocoloration of ZrO2, reactions that involved the photoreduction of molecular oxygen, the photooxidation of molecular hydrogen, the photooxidation of hydrogen by adsorbed oxygen, and the photoinduced transformation of ammonia and carbon dioxide. Kinetics of the photoprocesses are reported, as well as the photoinduced chesorluminscence (PhICL effect) of ammonia. Thermoprogrammed desorption and mass spectral monitoring of the photoreaction involving NH3 identified hydrazine as an intermediate and molecular nitrogen as the final product. The photoreactions involving NH3 and CO2 are nonphotocatalytic processes, in contrast to the photooxidation of hydrogen which is photocatalytic. Carbon dioxide and carbonate radical anions are formed by interaction of CO2 with Zr3+ centers and hole states (OS-*), respectively. Mechanistic implications are discussed.
Intracavity semiconductor saturable absorber mirrors (SESAM's)
offer unique and exciting possibilities for passively pulsed solid-state
laser systems, extending from Q-switched pulses in the nanosecond and
picosecond regime to mode-locked pulses from 10's of picoseconds to
sub-10 fs. This paper reviews the design requirements of SESAM's for
stable pulse generation in both the mode-locked and Q-switched regime.
The combination of device structure and material parameters for SESAM's
provide sufficient design freedom to choose key parameters such as
recovery time, saturation intensity, and saturation fluence, in a
compact structure with low insertion loss. We have been able to
demonstrate, for example, passive modelocking (with no Q-switching)
using an intracavity saturable absorber in solid-state lasers with long
upper state lifetimes (e.g., 1-μm neodymium transitions), Kerr lens
modelocking assisted with pulsewidths as short as 6.5 fs from a
Ti:sapphire laser-the shortest pulses ever produced directly out of a
laser without any external pulse compression, and passive Q-switching
with pulses as short as 56 ps-the shortest pulses ever produced directly
from a Q-switched solid-state laser. Diode-pumping of such lasers is
leading to practical, real-world ultrafast sources, and we will review
results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF,
Nd:LSB, and Nd:YVO<sub>4</sub>
We demonstrate the use of an optical thresholder based on a short length of holey fiber to achieve enhanced code recognition quality in a 255-chip 320-Gchip/s superstructured fiber Bragg grating-based optical code-division multiple access code:decode system. The nonlinear thresholder is based on bandpass filtering of spectrally broadened components generated by self-phase modulation and assisted by the Raman effect in an 8.7 m length of highly nonlinear holey fiber. Error free penalty free system performance is obtained with complete recovery of the original input pulse shape.
This paper describes a new class of saturable absorber device based on single-wall carbon nanotube (SWNT)-the saturable absorber incorporating nano tube (SAINT). The device possesses ultrafast optical properties comparable to that of the industrial standard semiconductor saturable absorber mirror (SESAM). Passively mode-locked picosecond fiber lasers in different configurations are demonstrated using SAINTs as mode lockers. This is the first demonstration of optical pulsed lasers based on the carbon nanotube technology, and the first practical application of carbon nanotubes in the field of applied optics.
We demonstrate an elementary grating-based optical code division multiple access (OCDMA) code generation and recognition system incorporating a nonlinear optical loop mirror (NOLM) within the receiver. We show that the NOLM can act as a nonlinear processing element capable of reducing both the pedestal associated with conventional matched filtering and the width of the associated code-recognition pulse. The pedestal rejection allows for an improved code recognition signal-to-noise ratio (SNR) relative to simple matched filtering alone, and reduced intra- and interchannel interference noise due to code overlap. The system benefits of using the NOLM are experimentally demonstrated under both single- and multiuser operation within a variety of seven- and 63-chip 160-Gchip/s code generation, recognition, and transmission experiments based on the use of bipolar superstructure fiber Bragg grating (SSFBG) coding-decoding pairs. Incorporation of the NOLM is shown to allow error-free penalty-free operation at data rates as high as 2.5 Gb/s under single-user operation, and to provide error-free performance with reduced power penalty in two-user experiments. The narrowed pulse recognition signature offers major advantages in terms of the further all-optical processing of decoded signals, such as code regeneration and recoding
This paper reports comprehensive experimental results on a
femtosecond code-division multiple-access (CDMA) communication system
test bed operating over optical fiber in the 1.5 μm communication
band. Our test bed integrates together several novel subsystems,
including low-loss fiber-pigtailed pulse shapers for encoding-decoding,
use of dispersion equalizing fibers in dispersion compensated links for
femtosecond pulse transmission and also in femtosecond chirped pulse
amplification (CPA) erbium doped fiber amplifiers (EDFAs), and
high-contrast nonlinear fiber-optic thresholders. The individual
subsystems are described, and single-user system level experimental
results demonstrating the ability to transmit spectrally encoded
femtosecond pulses over a 2.5-km dispersion compensated fiber link
followed by decoding and high contrast nonlinear thresholding are
presented
Investigations into 2D nanomaterials are of considerable significance from both an academic and industrial point of view. The present work addresses, for the first time, the fabrication of 2D nonlayered ultrathin selenium through a facile liquid-phase exfoliation method. The results reveal that the as-prepared 2D Se nanosheets are 40–120 nm in lateral dimension and 3–6 nm in thickness. The nanosheets exhibit a trigonal crystalline phase similar to their bulk counterpart, indicating the conservation of the crystalline features during the exfoliation procedure. The successful preparation of 2D Se nanosheets from nonlayered bulk Se can be ascribed to two kinds of anisotropy: (1) that of crystalline bulk Se with chain-like structures, where strong intrachain SeSe covalent bonds coexist with weak interchain van der Waals forces, and (2) that of probe sonication in the vertical direction. The results also show that the 2D Se nanosheets possess a size-dependent band gap (E g), strong photoluminescence effect and robust, chemical stability under ambient conditions. Furthermore, a 2D Se-nanosheet-based optical modulation device is demonstrated that allows for excellent ultrashort pulse generation of an optical communication band. It is therefore anticipated that 2D Se nanosheets may find significant applications in both photoluminescence and ultrafast photonics.
Discovery of graphene and its astonishing properties have given birth to a new class of materials known as “2D materials”. Motivated by the success of graphene, alternative layered and non-layered 2D materials have become the focus of intense research due to their unique physical and chemical properties. Origin of these properties ascribed to the dimensionality effect and modulation in their band structure. This review highlights the recent progress of the state-of-the-art research on synthesis, characterization and isolation of single and few layer nanosheets and their assembly. Electronic, magnetic, optical and mechanical properties of 2D materials have also been reviewed for their emerging applications in the area of catalysis, electronic, optoelectronic and spintronic devices; sensors, high performance electrodes and nanocomposites. Finally this review concludes with a future prospective to guide this fast evolving class of 2D materials in next generation materials science.
The discovery of graphene has triggered great interest in two-dimensional (2D) nanomaterials for scientists in chemistry, physics, materials science, and related areas. In the family of newly developed 2D nanostructured materials, 2D soft nanomaterials, including graphene, BxCyNz nanosheets, 2D polymers, covalent organic frameworks (COFs), and 2D supramolecular organic nanostructures, possess great advantages in light-weight, structural control and flexibility, diversity of fabrication approaches, and so on. These merits offer 2D soft nanomaterials a wide range of potential applications, such as in optoelectronics, membranes, energy storage and conversion, catalysis, sensing, biotechnology, etc. This review article provides an overview of the development of 2D soft nanomaterials, with special highlights on the basic concepts, molecular design principles, and primary synthesis approaches in the context.
Under strong laser radiation, a Dirac material, the topological insulator (TI) Bi2Te3, exhibits an optical transmittance increase as a result of saturable absorption. Based on an open-aperture Z-scan measurement at 1550 nm, we clearly show that the TI, Bi2Te3 under our investigation, is indeed a very-high-modulation-depth (up to 95%) saturable absorber. Furthermore, a TI based saturable absorber device was fabricated and used as a passive mode locker for ultrafast pulse formation at the telecommunication band. This contribution unambiguously shows that apart from its fantastic electronic property, a TI (Bi2Te3) may also possess attractive optoelectronic property for ultrafast photonics.
In this paper, we present a tutorial introduction to optical microfibers and nanofibers regarding their optical properties, fabrication and applications, with a brief outlook into future trends in this area.
Employing graphene as an intracavity passive power modulating element, we demonstrate the efficient laser pulsation in high pulse-energy regime with evanescent field interaction between the propagating light and graphene layer. Graphene is prepared by the solution based reduction of graphene oxide, and dispersed homogeneously into the water for spray onto an all-fiber substrate, side-polished fiber. With the intracavity power up to 21.41 dBm, we ensure the robust high-energy operation without any thermal damage of graphene. Resultant output pulses have center wavelength, spectral width, and repetition rate of 1561.6 nm, 1.96 nm, and 6.99 MHz, respectively.
a b s t r a c t A study on p-doping of organic wide band gap materials with Molybdenum trioxide using current transport measurements, ultraviolet photoelectron spectroscopy and inverse pho-toelectron spectroscopy is presented. When MoO 3 is co-evaporated with 4,4 0 -Bis(N-carbaz-olyl)-1,1 0 -biphenyl (CBP), a significant increase in conductivity is observed, compared to intrinsic CBP thin films. This increase in conductivity is due to electron transfer from the highest occupied molecular orbital of the host molecules to very low lying unfilled states of embedded Mo 3 O 9 clusters. The energy levels of these clusters are estimated by the energy levels of a neat MoO 3 thin film with a work function of 6.86 eV, an electron affinity of 6.7 eV and an ionization energy of 9.68 eV. The Fermi level of MoO 3 -doped CBP and N,N 0 -bis(1-naphtyl)-N,N 0 -diphenyl-1,1 0 -biphenyl-4,4 0 -diamine (a-NPD) thin films rapidly shifts with increasing doping concentration towards the occupied states. Pinning of the Fermi level several 100 meV above the HOMO edge is observed for doping concentrations higher than 2 mol% and is explained in terms of a Gaussian density of HOMO states. We determine a relatively low dopant activation of $0.5%, which is due to Coulomb-trapping of hole car-riers at the ionized dopant sites.
The electronic structures of the two polymorphic forms of lead monoxide (PbO), red tetragonal ..cap alpha..-PbO and yellow orthorhombic ..beta..-PbO, are investigated by using extended Hueckel tight-binding calculations. The band structures and bonding are analyzed within the layers and also for the complete three-dimensional solids. In red ..cap alpha..-PbO a local energy minimum is obtained when the layers are stacked together. For yellow ..beta..-PbO, the bonding is studied starting from PbO subunits and building successively chains, layers, and the three-dimensional solid. Bonding between chains occurs mainly through Pb-O but Pb-Pb bonding interactions are also significant. In both ..cap alpha.. and ..beta.. modifications weak interlayer Pb-Pb bonding is found which may not be the result of van der Waals attraction. Crystal orbital overlap populations provide a convenient view of the bonding in the two solids. Within the layers, these values correlate satisfactorily with the force constants calculated from experimental data. It is suggested that a more strongly bound material could be synthesized if either PbO structure should have electrons removed from it.
Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness and infinite planar lengths, are regarded as the thinnest functional nanomaterials. The recent development of methods for manipulating graphene (carbon nanosheet) has provided new possibilities and applications for 2D systems; many amazing functionalities such as high electron mobility and quantum Hall effects have been discovered. However, graphene is a conductor, and electronic technology also requires insulators, which are essential for many devices such as memories, capacitors, and gate dielectrics. Along with graphene, inorganic nanosheets have thus increasingly attracted fundamental research interest because they have the potential to be used as dielectric alternatives in next-generation nanoelectronics. Here, we review the progress made in the properties of dielectric nanosheets, highlighting emerging functionalities in electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanoelectronics.
The optical conductance of monolayer graphene is defined solely by the fine structure constant. The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, we demonstrate the use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the thickness of graphene. Our results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth and wideband tuneability.
Graphene is at the center of a significant research effort. Near-ballistic transport at room temperature and high mobility make it a potential material for nanoelectronics. Its electronic and mechanical properties are also ideal for micro- and nanomechanical systems, thin-film transistors, and transparent and conductive composites and electrodes. Here we exploit the optoelectronic properties of graphene to realize an ultrafast laser. A graphene-polymer composite is fabricated using wet-chemistry techniques. Pauli blocking following intense illumination results in saturable absorption, independent of wavelength. This is used to passively mode-lock an erbium-doped fiber laser working at 1559 nm, with a 5.24 nm spectral bandwidth and approximately 460 fs pulse duration, paving the way to graphene-based photonics.
Mode-locked sub-picosecond operation of Yb-, Er- and Tm:Hodoped fiber lasers operating at 1.05 microm, 1.56 microm and 1.99 microm, respectively, is demonstrated using the same sample carbon nanotube-based saturable absorber mirror. A mesh of single-walled carbon nanotubes was deposited on an Ag-mirror using a one-step dry-transfer contact press method to combine broadband saturable absorption and high reflectance properties. The novel fabrication method of the polymer-free absorber and device parameters determined using nonlinear reflectivity measurement are described in detail. To our knowledge the observed operation bandwidth of approximately 1 microm is the broadest reported to date for a single carbon nanotube-based saturable absorber.
We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions,
metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between
valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in
concentrations up to 1013 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by
applying gate voltage.
The periodic amplification of solitons is shown to develop an instability. This becomes evident through the appearance of a series of discrete sidebands in the soliton power spectrum. These sidebands do not exhibit the power tuning characteristic of the modulational instability, but instead follow an inverse square root dependence on the amplification period.