Recent realization of nontrivial topological phases in photonic systems has provided unprecedented opportunities in steering light flow in novel manners. Based on the Su-Schriffer-Heeger (SSH) model, a topologically protected optical mode was successfully demonstrated in a plasmonic waveguide array with a kinked interface that exhibits a robust nonspreading feature. However, under the same excitation conditions, another antikinked structure seemingly cannot support such a topological interface mode, which appears to be inconsistent with the SSH model. Theoretical calculations are carried out based on the coupled-mode theory, in which the mode properties, excitation conditions, and the robustness are studied in detail. It is revealed that under the exact eigenstate excitations, both kinked and antikinked structures do support such robust topological interface modes; however, for a realistic single-waveguide input only the kinked structure does so. It is concluded that the symmetry of interface eigenmodes plays a crucial role, and the odd eigenmode in a kinked structure offers the capacity to excite the nonspreading interface mode in the realistic excitation of a one-waveguide input. Our finding deepens the understanding of mode excitation and propagation in coupled waveguide systems, and could open a new avenue in optical simulations and photonic designs.

Recent progresses on Floquet topological phases have shed new light on time-dependant quantum systems, among which one-dimensional (1D) Floquet systems have been under extensive theoretical research. However, an unambiguous experimental observation of these 1D Floquet topological phases has still been lacking. Here, by periodically bending ultrathin metallic arrays of coupled corrugated waveguides, a photonic Floquet simulator was well designed and successfully fabricated to simulate the periodically driven Su-Schrieffer-Heeger model. Intriguingly, under moderate driven frequencies, we first experimentally observed and theoretically verified the Floquet topological π mode propagating along the array's boundary. The different evolutionary behaviors between static and non-static topological end modes have also been clearly demonstrated. Our experiment also reveals the universal high-frequency behavior in perically driven systems. We emphasize that, our system can serve as a powerful and versatile testing ground for various phenomena related to timedependant 1D quantum phases, such as Thouless charge pumping and manybody localization. arXiv:1804.05134v2 [quant-ph]

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Electromagnetic waves carrying orbital angular momentum (OAM), namely, vortex beams, have a plethora of applications ranging from rotating microparticles to high‐capacity data transmissions, and it is a continuing trend in manipulating OAM with higher degrees of freedom. Here, an approach to control terahertz (THz) near‐field plasmonic vortex based on geometric and dynamic phase is proposed and experimentally demonstrated. By locally tailoring the orientation angle (geometric phase) and radial position (dynamic phase) of aperture arrays embedded in an ultrathin gold film, the excited surface waves can be flexibly engineered to form both spin‐independent and spin‐dependent THz plasmonic vortex field distributions, resulting in multi‐degree of freedom for controlling OAM of THz surface plasmon polaritons (SPPs). Arbitrary OAM values of THz plasmonic vortex and coherent superposition between two OAM states are investigated based on near‐field scanning terahertz microscopy (NSTM) system. The proposed approach provides unprecedented freedom to modulate THz near‐field plasmonic vortex, which will have potential applications in THz communications and quantum information processing.

), the authors prove a best proximity point theorem for Geraghty nonself contraction. In this note, not only P-property has been weakened, but also an improved best proximity point theorem will be presented by a short and simple proof. An example which satisfies weak P-property but not P-property has been presented to demonstrate our results. MSC: 47H05; 47H09; 47H10

We theoretically studied a nonlinear optical process in a hybrid plasmonic waveguide composed of a nonlinear dielectric waveguide and a metal film with a separation of a thin air gap. Owing to the hybridization effect of guided mode and surface plasmon polariton mode, this particular waveguide is able to confine the optical-field in a deep subwavelength scale together with low propagation loss. Based on this, efficient second-harmonic generations (SHG) were revealed at the fundamental wavelength of λ=1.55 μm with good field confinement. The SHG efficiency, as well as the coupling coefficient and mode area, were analyzed and discussed in detail with respect to the structural parameters.

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Terahertz beam splitters and polarization rotators are two typical devices with wide applications ranging from terahertz communication to system integration. However, they are faced with severe challenges in manipulating THz waves in multiple channels, which is desirable for system integration and device miniaturization. Here, we propose a method to design ultra-thin multi-channel THz beam splitters and polarization rotators simultaneously. The reflected beams are divided into four beams with nearly the same density under illumination of linear-polarized THz waves, while the polarization of reflected beams in each channel is modulated with a rotation angle or invariable with respect to the incident THz waves, leading to the multi-channel polarization rotator (multiple polarization rotation in the reflective channels) and beam splitter, respectively. Reflective metasurfaces, created by patterning metal-rods with different orientations on a polyimide film, were fabricated and measured to demonstrate these characteristics. The proposed approach provides an efficient way of controlling polarization of THz waves in various channels, which significantly simplifies THz functional devices and the experimental system.