Data capacity is rapidly reaching its limit in modern optical communications. Optical vortex has been explored to enhance the data capacity for its extra degree of freedom of angular momentum. In traditional means, optical vortices are generated using space light modulators or spiral phase plates, which would sharply decrease the integration of optical communication systems. Here we experimentally demonstrate a planar chiral antenna array to produce optical vortex from a circularly polarized light. Furthermore, the antenna array has the ability to focus the incident light into point, which greatly increases the power intensity of the generated optical vortex. This chiral antenna array may have potential application in highly integrated optical communication systems.

We present a general theory of effective media to set up the relationship between the particle responses and the macroscopic system behaviors for artificial metamaterials composed of periodic resonant structures. By treating the unit cell of the periodic structure as a particle, we define the average permittivity and permeability for different unit structures and derive a general form of discrete Maxwell's equations on the macroscale, from which we obtain different wave modes in metamaterials including the propagation mode, pure plasma mode, and resonant crystal band-gap mode. We explain unfamiliar behaviors of metamaterials from the numerical S parameter retrieval approach. The excellent agreement between theoretical predictions and retrieval results indicates that the defined model and method of analysis fit the physical structures very well. Thereafter, we propose a more advanced form of the fitting formulas for the effective electromagnetic parameters of metamaterials.

and holographic plates. [12,13] Nevertheless, most of aforementioned metasurfaces are composed of passive metaparticles and generally behave one EM functionality, which cannot satisfy the largely increasing demand of multifunctional devices. Although several substantial efforts have been devoted to combine the multiple EM functionalities into one single metasurface, the realized multifunctionalities can only be acquired at different polarization states or frequencies. [14][15][16][17][18] More recently, much more attention has been focused on the design of reconfigurable metasurfaces by employing tunable metaparticles driven by thermal effect, [19,20] electrical tuning, [21,22] mechanically stretching, [23,24] and so on. The realistic possibility of reconfigurable metasurfaces has been demonstrated in optical, terahertz, and microwave regions, accompanied by the emergence of interesting applications, such as beam steering, [25,26] tunable absorbing, [27,28] chiral polarization switching, [29,30] and so on. The reconfigurability of metasurface in optical and terahertz domains is generally realized by exploiting the active medias, including graphene, [31] liquid crystal, [32] vanadium dioxide, [33] and Ge 2 Sb 2 Te 5 (GST). [34,35] In the microwave region, metasurfaces achieve the tunable EM responses through the general method of integrating discrete elements such as varactor diodes, [36,37] PIN diode switches, [38,39] and MEMS switches [40] within the metaparticles. In ref.[28], the metasurface with varactor diodes involved was proposed to tune the absorbing frequency. In ref.[38], the PIN diodes were adopted to design the polarization-reconfigurable metasurface that can dynamically control the handedness of the circularly polarized wave. The above lumped components have also been used to achieve the dynamical control of EM wavefront. [40] However, most of the realized tunable metasurface focused on the reconfiguration of a single one function (e.g., absorbing frequency, polarization feature, and beam deflection angle). The latest efforts started to be devoted to the design of multifunctional metasurface that integrates diversified functionalities into a monolayer metastructure. [39,41] In ref.[39], microelectromechanical system (MEMS) technology was utilized to construct the metasurface with tunable resonance for obtaining 360° phase span, and based on the phase modulation, the multifunctionalities, including polarization control, wavefront deflection and holograms, have been numerically demonstrated. In ref.[41], a programmable metasurface was reported Metasurfaces provide a novel strategy to manipulate electromagnetic (EM) waves by controlling the local phase of subwavelength artificial structures within the wavelength scale. So far, many exciting devices have been developed and most of them are based on passive metasurface, which can only perform a specific functionality. It is still very challenging to simultaneously achieve multiple EM functionalities and real-time reconfigurability in one design. This stud...

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Micro/nanoprocessing of graphene surfaces has attracted significant interest for both science and applications due to its effective modulation of material properties, which, however, is usually restricted by the disadvantages of the current fabrication methods. Here, by exploiting cylindrical focusing of a femtosecond laser on graphene oxide (GO) films, we successfully produce uniform subwavelength grating structures at high speed along with a simultaneous in situ photoreduction process. Strikingly, the well-defined structures feature orientations parallel to the laser polarization and significant robustness against distinct perturbations. The proposed model and simulations reveal that the structure formation is based on the transverse electric (TE) surface plasmons triggered by the gradient reduction of the GO film from its surface to the interior, which eventually results in interference intensity fringes and spatially periodic interactions. Further experiments prove that such a regular structured surface can cause enhanced optical absorption (>20%) and an anisotropic photoresponse (~0.46 ratio) for the reduced GO film. Our work not only provides new insights into understanding the laser-GO interaction but also lays a solid foundation for practical usage of femtosecond laser plasmonic lithography, with the prospect of expansion to other two-dimensional materials for novel device applications.

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An efficient auxiliary-differential equation (ADE) form of the complex frequency shifted perfectly matched layer (CPML) absorbing media derived from a stretched coordinate PML formulation is presented. It is shown that a unit step response of the ADE-CPML equations leads to a discrete form that is identical to Roden's convolutional PML method for FDTD implementations. The derivation of discrete difference operators for the ADE-CPML equations for FDTD is also presented. The ADE-CPML method is also extended in a compact form to a multiple-pole PML formulation. The advantage of the ADE-CPML method is that it provides a more flexible representation that can be extended to higher-order methods. In this paper, it is applied to the discontinuous Galerkin finite element time-domain (DGFETD) method. It is demonstrated that the ADE-CPML maintains the exponential convergence of the DGFETD method.Index Terms-Absorbing boundary conditions, finite-difference time-domain (FDTD) methods, finite element methods, perfectly matched layer.