关键词：
Black phosphorus quantum dots (BPQDs);bound soliton;fiber laser;saturable absorber;mode-locking
摘要：
We have investigated the nonlinear and ultrafast photonics of chemically processed black phosphorus quantum dots (BPQDs) synthesized by the solvothermal treatment approach, with an average lateral size of about 2.48 +/- 0.4 nm. BPQDs exhibit optical saturable absorption measured by the balanced twin-detector measurement system at the telecommunication band and have been demonstrated for the generation of passively mode-locking operation in an erbium-doped fiber laser. Either two-pulse or three-pulse bound state of soliton pulse has been obtained, making the best use of the BPQDs-based saturable absorber. Our work suggests that BPQDs might be developed as an efficient optical saturable absorber for ultrafast photonics applications.
摘要：
In this work, we theoretically propose an optical biosensor (consists of a BK7 glass, a metal film, and a graphene sheet) based on photonic spin Hall effect (SHE). We establish a quantitative relationship between the spin-dependent shift in photonic SHE and the refractive index of sensing medium. It is found that, by considering the surface plasmon resonance effect, the refractive index variations owing to the adsorption of biomolecules in sensing medium can effectively change the spin-dependent displacements. Remarkably, using the weak measurement method, this tiny spin-dependent shifts can be detected with a desirable accuracy so that the corresponding biomolecules concentration can be determined.
摘要：
The emerging invisibility schemes mainly adopt transformation optics, scattering cancellation, light diffusion, and metasurface-based phase restoration techniques. However, those aforementioned invisibility achievements natively depend on the predefined curvature, polarization, frequency, and/or angle of the incident wave. Here, an invisibility strategy of using an ultrathin parabolic-phase metasurface and its applications to achieve diffusive invisibility for dual-polarization channels and multifrequency channels is reported. Such strategy can intrinsically split the wavenumber of the scattering wave and therein is termed as wavenumber-splitting metasurface. For verification, two proof-of-concept examples are experimentally characterized. The first prototype manifests dual-polarized near-isotropic diffusive scattering immune from wide-angle incidences. The second demonstration exhibits bifunctionality of combined diffusive invisibility and vortex scattering in dual-polarization channels. In both cases, theoretical, numerical and experimental results agree well, illustrating a well-separated triple-band versatile scattering behavior. This approach addresses the fundamental issue of real invisibility under bistatic detection without complex optimization, thanks to the physical essence of numerous splitting wave vectors. Such strategy opens an upstream way to realize invisibility as well as holding the potentials for downstream applications such as stealth and camouflaging devices.
摘要：
A two-dimensional (2D) MoSi2N4 monolayer is an emerging class of air-stable 2D semiconductors possessing exceptional electrical and mechanical properties. Despite intensive recent research effort devoted to uncover the material properties of MoSi2N4, the physics of electrical contacts to MoSi2N4 remains largely unexplored thus far. In this work, we study van der Waals heterostructures composed of MoSi2N4 contacted by graphene and NbS2 monolayers using first-principles density functional theory calculations. We show that the MoSi2N4/NbS2 contact exhibits an ultralow Schottky barrier height (SBH), which is beneficial for nanoelectronics applications. For the MoSi2N4/graphene contact, the SBH can be modulated via the interlayer distance or via external electric fields, thus opening up an opportunity for reconfigurable and tunable nanoelectronic devices. Our findings provide insights into the physics of 2D electrical contacts to MoSi2N4 and shall offer a critical first step toward the design of high-performance electrical contacts to MoSi2N4-based 2D nanodevices.
摘要：
A new type of broadband saturable absorber made of graphene-Bi2Te3 heterostructure was reported, which synergistically combines light-matter interaction in graphene with that in a small bandgap semiconductor material Bi2Te3 to achieve an improved broadband nonlinear optical response. The graphene-Bi2Te3 heterostructure films were grown by chemical vapor deposition with 15% Bi2Te3 coverage on graphene, in which most of the Bi2Te3 nanoplatelets are less than 30 nm thick. It is interesting to find that the heterostructure thin film shows broadband saturable absorption property. At the communication band (around 1560 nm), the saturable intensity and modulation depth are measured to be 4.95 MW/cm(2) and 18.98%, respectively. While around 1067 nm, the corresponding saturable intensity and modulation depth are experimentally measured to be 2.61 MW/cm(2) and 23.11%, respectively. By incorporating this optical saturable absorber inside either an Er-doped or Yb-doped fiber laser, we are able to generate ultra-short pulse with very stable operation at 1565.6 and 1049.1 nm. Our experimental results clearly demonstrate that the graphene-Bi2Te3 heterostructure can be a promising broadband nonlinear optical material for broadband ultra-fast laser photonics.
摘要：
Organic-inorganic hybrid perovskite solar cells (SCs) have emerged as one of the most promising contenders to traditional silicon solar cells, due to their active layers outstanding photoelectric properties, such as appropriate direct bandgap, balanced high carrier mobility and long carrier diffusion length, the identified power conversion efficiency (PCE) has reached to 22.7%. But the toxic lead, a key component in the archetypical light harvesting material, is a large obstacle to commercialization. Herein, we reviewed the recent progress in lead-free perovskite (-like) SCs according to the valent difference of metal ions in absorber material, e.g., bivalent (Sn2+, Ge2+, Cu2+, Sr2+), trivalent (Bi3+, Sb3+), tetravalent (Sn4+) and hybrid valent (e.g. Ag+ and Bi3+). Finally, we gave an outlook on the tactic to achieve high performance lead-free perovskite (-like) SCs. (c) 2018 Elsevier Ltd. All rights reserved.
通讯机构：
[Wang, Xin-Wen] H;Hengyang Normal Univ, Dept Phys & Elect Informat Sci, Hengyang 421008, Peoples R China.
摘要：
The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years much effort has been made to perform multiqubit gates via weak XKNLs. However, the required nonlinearity strengths are still difficult to achieve in an experiment. We here propose an XKNL-based scheme for realizing a two-photon polarization-parity gate, a universal two-qubit gate, in which the required strength of the nonlinearity could be orders of magnitude weaker than those required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state as a quantum information bus which interacts with a path mode of the two polarized photons (qubits). The XKNL effect makes the bus pick up a phase shift dependent on the photon number of the path mode. Even when the potential phase shifts are very small they can be effectively measured using photon-number resolving detectors, which accounts for the fact that our scheme can work in the regime of tiny XKNL. The measurement outcome reveals the parity (even parity or odd parity) of the two polarization qubits.
作者机构：
[Wang, Yanzhao; Xu, He-Xiu; Wang, Chaohui] Air Force Engn Univ, Dept Elect Sci & Technol, Xian 710051, Shaanxi, Peoples R China.;[Hu, Guangwei; Jiang, Menghua] Natl Univ Singapore, Dept Elect & Comp Engn, Singapore 117583, Singapore.;[Tang, Shiwei] Ningbo Univ, Dept Phys, Fac Sci, Ningbo 315211, Zhejiang, Peoples R China.;[Huang, Yongjun] Univ Elect Sci & Technol, Sch Informat & Commun Engn, Chengdu 611731, Sichuan, Peoples R China.;[Ling, Xiaohui] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421002, Peoples R China.
通讯机构：
[Xu, He-Xiu] A;Air Force Engn Univ, Dept Elect Sci & Technol, Xian 710051, Shaanxi, Peoples R China.
关键词：
dual mode;dynamic and geometric phase;multiplexed metasurfaces;spin decoupling;wavefront control
摘要：
Achieving kaleidoscopic wavefront controls with a thin flat plate is pivotal for increasing data capacity yet still challenging in integrated optics. An anisotropic metasurface provides an efficient recipe primarily for linear polarization, but is less efficient for multiple functionalities at arbitrary spin states. Here, a strategy of realizing a spin-decoupled high-capacity multifunctional metasurface by multiplexing the frequency and wavevector degree of freedom (DoF) is reported. By integrating both geometric and dynamic phases in split ring resonators and crossbars in a chessboard configuration, the inherent limitation of spin-flipped Pancharatnam-Berry phases can be completely decoupled between two spin states. Such released extraordinary DoF unprecedentedly increases the capability to yield kaleidoscopic wavefront control. To verify the significance, two proof-of-concept metadevices that are nearly impossible in conventional metasurfaces are experimentally demonstrated with four-port wavefront manipulations, exhibiting spin-, frequency-, and wavevector-dependent anomalous reflections, lensing, orbital angular momentum generation, and wavevector-multiplexed vortex scattering, along with two-dimensional holograms. Both numerical and experimental results illustrate quad-distinct functionalities with up to ten channel beams and approximate to 93% efficiency, because of the completely suppressed crosstalk among different operation modes, angular wavevectors, and spins. The finding in triple-DoF multiplexing is expected to generate great interest in electromagnetic integration with emerging DoFs.
作者机构：
[Zhang, Deng-Yu; Xu, Zhi-Feng; Tang, Zhen-Kun] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421008, Peoples R China.;[Zhang, Deng-Yu; Xu, Zhi-Feng; Tang, Zhen-Kun] Hengyang Normal Univ, Coll Chem & Mat Sci, Hengyang 421008, Peoples R China.;[Hu, Shu-Xian; Lau, Woon-Ming; Tang, Zhen-Kun; Liu, Li-Min] Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.;[Lau, Woon-Ming] Univ Sci & Technol Beijing, Sch Math & Phys, Ctr Green Innovat, Beijing 100083, Peoples R China.
通讯机构：
[Liu, Li-Min] B;Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.
摘要：
The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH2) 2PbI3 (FAPbI(3)) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH3NH3PbI3 (MAPbI(3)) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI(3)/FAPbI(3) structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI(3)/FAPbI(3) is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI(3)/FAPbI(3). More importantly, compare with the un-doped tetragonal MAPbI(3)/FAPbI(3), the Sn-doped MAPbI(3) and FAPbI(3) have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sndoped FAPbI(3). The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI(3) make it promising candidates for high-efficient perovskite cells.
