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Recently, tremendous remarkable studies on spin–orbit interactions (SOIs) have attracted interest of scientists across the world in various fields. Among contemporary technologies of probing SOI, photonic metasurfaces have become a prevalent tool to guide and steer wavefront of light at the subwavelength scale. Nevertheless, the discretized nanoantennas of metasurfaces have been plagued for the shortcoming of bandwidth. In contrast to the discretized strategy, symmetric nanorings possessing a continuous phase gradient are exploited in this work. Benefiting from lossless dielectric material and nondispersive characteristic of the Pancharatnam–Berry phase principle, the designer nanorings are viable to realize high efficient spin-to-vortex conversion over a wide spectrum. The nanorings also accomplish a high purity of orbit angular momentum mode, which is of vital importance in many applications. Our findings would be beneficial to delve spin-controllable nanodevices and hold promise for applications of atomic manipulation and optical tweezers. [ABSTRACT FROM AUTHOR]

• Pneumatic control of the coupling between the two split rig resonators. • Reduced electromagnetic interference and improved stability. • 28% of the resonance frequency tuning. We have investigated the operation of a coupled system of double split ring resonators (SRRs) to demonstrate the tunability by changing its physical layout. A pneumatic system is proposed to dynamically shift the structural arrangement of the coupled SRRs in response to the incident electromagnetic wave. It is executed by manipulating the lateral placement of the levitated bottom ring relative to the static ring in the top layer using various levels of pneumatic force. We reduced the electromagnetic interference by avoiding metallic components and improved the stability through the contactless operation. The proposed pneumatic system uses only the air to modulate the operational frequency of the coupled SRRs. Both the simulation and the experiment have shown the transition between the quasi-edge coupled and the broad-side coupled modes of the double SRRs shift the resonance frequency over 28% around 3.0 GHz. This pneumatic implementation brings a new method of reconfigurable SRRs. [ABSTRACT FROM AUTHOR]

Dark-field illumination is shown to make planar chiral nanoparticle arrangements exhibit circular dichroism in extinction, analogous to true chiral scatterers. Single oligomers, consisting rotationally symmetric arrangements of gold nanorods, are experimentally observed to exhibit circular dichrosim at their maximum scattering with strong agreement to numerical simulation. A dipole model is developed to show that this effect is caused by a difference in the projection of a nanorod onto the handed orientation of electric fields created by a circularly polarized dark-field normally incident on a glass-air interface. Owing to this geometric origin, the wavelength of the peak chiral response is experimentally shown to shift depending on the separation between nanoparticles. All presented oligomers have physical dimensions less than the operating wavelength, and the applicable extension to closely packed planar arrays of oligomers is demonstrated to amplify the magnitude of circular dichroism. This realization of strong chirality in these oligomers demonstrates a new path to engineer optical chirality from planar devices using dark-field illumination. [ABSTRACT FROM AUTHOR]

We report the geometric dependences of metal-coated silicon nanowire (Si NW) plasmonic waveguides on their propagation lengths and mode areas. We examined Si NWs with four different cross-sectional shapes. Numerical simulations showed that propagation lengths and mode areas are highly dependent on the cross-sectional geometries of Si NWs. In particular, the TM-like mode in a hexagonal-shaped Si NW plasmonic waveguide without an air void has the longest propagation length of 18.20 μm, which is 4.7 times larger than that of the TM-like mode in a circular-shaped Si NW plasmonic waveguide. This study can be a useful guide for the design and application of metal-coated Si NW plasmonic waveguides. [ABSTRACT FROM AUTHOR]

Abstract: The authors introduce frequency selective beam splitters for surface plasmon polaritons (SPPs) in a metal-insulator-metal (MIM) structure. In the splitters, a part of SPPs keeps propagating straight along the initial direction, while the other part is split into the arm attached at right angle. The splitting ratio can be controlled by varying the width and the electric permittivity of the dielectric layer in the MIM, and by varying the width of the attached arm. [Copyright &y& Elsevier]

We propose a complementary split-ring resonator (CSRR) for a directional coupling of surface plasmon polaritons. An air-slot split-ring in a gold film is investigated using the finite-difference time-domain method. The normally incident light couples to either a monopole or a dipole SPP depending on the polarization of light. Adjusting the angle of the linear polarization of the incident light enables a one-way propagation of SPPs on the gold film. Theoretical analysis based on the propagation of cylindrical waves from the SPP point source is provided with Hankel function. The propagated power in one direction is obtained to be 30 times higher than the opposite direction with a coupling efficiency of 18.2% from the simulation for an array of the CSRRs. This approach to the directional coupling of SPPs will be advantageous for miniaturizing photonic and plasmonic circuits and devices. [ABSTRACT FROM AUTHOR]

Growing interest in devices based on layered van der Waals (vdW) materials is motivating the development of new nanofabrication methods. Hexagonal boron nitride (hBN) is one of the most promising materials for studies of quantum photonics and phonon polaritonics. A promising nanofabrication process used to fabricate several hBN photonic devices using a hybrid reactive ion etching (RIE) and electron beam‐induced etching (EBIE) technique is reported in detail here. The shortcomings and benefits of RIE and EBIE are highlighted and the utility of the hybrid approach for the fabrication of suspended and supported device structures with nanoscale features and highly vertical sidewalls are demonstrated. Functionality of the fabricated devices is proven by measurements of high‐quality cavity optical modes (Q ≈ 1500). This nanofabrication approach constitutes an advance toward an integrated, monolithic quantum photonics platform based on hBN and other layered vdW materials. Various photonic nanostructures from hexagonal boron nitride (hBN) including photonic crystal cavities, microrings, and waveguides are presented. The report details a novel nanofabrication procedure for hBN utilizing reactive ion etching and electron beam‐induced etching. A suitable strategy is outlined to achieve high device functionalities. This is demonstrated by optical measurements of a photonic crystal cavity and microring resonator. [ABSTRACT FROM AUTHOR]

Abstract: Plasmonic devices offer the possibility of passively detecting changes in local chemistry that opens up a wide range of applications from molecular sensing to monitoring water quality. Conventional plasmonics have previously shown great promise as nanoscale chemical sensors through detection of small variations in the local refractive index (RI). The motivation behind using plasmonics for these applications includes the fact that detection is entirely passive and the devices themselves can be readily miniaturized. Previously, a lack of any control over the output of these devices, has fundamentally limited their application to chemicals which produce clearly identifiable resonances within the range of detection. Here it is demonstrated that microfluidic devices, incorporating polarization‐controlled plasmonic nanopixels, allow the device response to be tuned to the particular analyte of interest, anywhere within the visible spectrum. This dramatically increases the effective dynamic range and allows local variations in RI to be perceived directly as color changes by the human eye. Active control over the output of the device also enables clear differentiation between a number of different analytes, paving the way for plasmonics to be used for a wide range of real‐world chemical sensing applications. [ABSTRACT FROM AUTHOR]