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Multifocal lens, which focus incident light at multiple foci, are widely used in imaging systems and optical communications. However, for the traditional design strategy, it combines several lenses that have different focal points into a planar integrated unit, resulting a low imaging quality due to the high background noise. Here, we propose two kinds of multifocal metalens with Au nanoslits arranged in an elliptical and a hyperbolic shape, which are able to effectively focus incident light at all of the foci with constructive interference, and extremely decrease the background noise and improve the lens imaging performance at the nanoscale. We further demonstrate that, the proposed metalens can possess a broadband operation wavelength changed from 600 nm to 900 nm, with its dual-polarity actively controlled by the incident circular polarization lights. With great agreement between the experimental and simulation results, our proposed conic-shaped metalens provides a significant potential for the future integrated nanophotonic device., Comment: 23 pages, 5 figures

Molybdenum disulfide (MoS2) monolayers have attracted much attention for their novel optical properties and efficient light-matter interactions. When excited by incident laser, the optical response of MoS2 monolayers was effectively modified by elementary photo-excited excitons owing to their large exciton binding energy, which can be facilitated for the optical-controllable exciton-plasmon interactions. Inspired by this concept, we experimentally investigated active light control of surface plasmon resonance (SPR) in MoS2-Ag hybrid nanostructures. The white light spectra of SPR were gradually red-shifted by increasing laser power, which was distinctly different from the one of bare Ag nanostructure. This spectroscopic tunability can be further controlled by near-field coupling strength and polarization state of light, and selectively applied to the control of plasmonic dark mode. An analytical Lorentz model for photo-excited excitons induced modulation of MoS2 dielectric function was developed to explain the insight physics of this SPR tunability. Our study opens new possibilities to the development of all-optical controlled nanophotonic devices based on 2D materials., Comment: 27 pages, 6 figures

Ellipse and hyperbola are two well-known curves in mathematics with numerous applications in various fields, but their properties and inherent differences in spin optics are less understood. Here, we investigate the peculiar optical spin properties of the two curves and establish a connection between their foci and the spin states of incident light. We show that the optical spin Hall effect is the intrinsic optical spin property of ellipse, where photons with different spin states can be exactly separated to each of its two foci. While a hyperbola exhibits optical spin-selective effect, where only photons with one particular spin state can be accumulated at its foci. These properties are then experimentally demonstrated in near field by arranging nanoslits in conic shape. Based on the spin properties of the curves, we design spin-based plasmonic devices with various functionalities. Our results reveal the intrinsic optical spin properties behind conic curves and provide a route for designing spin-based plasmonic device., Comment: 19 pages, 4 figures

The Fano resonance of a single symmetry broken Ag nanodisk under a normal incidence was investigated by using finite-difference time-domain (FDTD) simulations. The asymmetry line shape of the Fano resonance was controlled by modifying the open angle of the nanodisk, and this Fano splitting was demonstrated as the result of the overlap between the broad dipolar and narrow quadrupolar modes, which could be strengthened by enlarging the radius of the nanodisk. A semi-analytical method was developed to calculate the plasmon hybridization, which was used to analyze the sub-process of the quadru Fano resonance. With the good agreement between theoretical calculations and FDTD simulations, the suggested method provides a way to investigate and control the Fano resonance inside a single planar nanostructure, and can be applied to the future high-performance Fano resonance sensors., Comment: 8 pages, 5 figures