Plasmonic edge states: an electrostatic eigenmode description

We consider periodic arrangements of metal nanostructures and study the effect of periodicity on the localised surface plasmon resonance of the structures within an electrostatic eigenmode approximation. We show that within this limit, the collective surface plasmon resonances of the periodic structures can be expressed in terms of superpositions of the eigenmodes of uncoupled nanostructures that exhibit a standing--wave character delocalised across the entire periodic structure. The formalism derived successfully enables the design and accounts for the observation of plasmonic edge-states in periodic structures

Optical chirality from dark-field illumination of planar plasmonic nanostructures

Dark-field illumination is shown to make planar chiral nanoparticle arrangements exhibit circular dichroism in extinction analogous to true chiral scatterers. Circular dichrosim is experimentally observed at the maximum scattering of single oligomers consisting rotationally symmetric arrangements of gold nanorods, with strong agreement to numerical simulation. A dipole model is developed to show that this effect is caused by a difference in the geometric projection of a nanorod onto the handed orientation of electric fields created by a circularly polarized dark-field that is normally incident on a glass substrate. Owing to this geometric origin, the wavelength of the peak chiral response is also 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. The realization of strong chirality in these oligomers demonstrates a new path to engineer optical chirality from planar devices using dark-field illumination

Evolution of topological edge modes from honeycomb photonic crystals to triangular-lattice photonic crystals

The presence of edge modes at the interface of two perturbed honeycomb photonic crystals with C6 symmetry is often attributed to the different signs of Berry curvature at the K and K′ valleys. In contrast to the electronic counterpart, the Chern number defined in photonic valley Hall effect is not a quantized quantity but can be tuned to a finite value including zero simply by changing geometrical perturbations. Here, we argue that the edge modes in photonic valley Hall effect can exist even when Berry curvature vanishes. We numerically demonstrate the presence of the zero-Berry-curvature edge modes in triangular-lattice photonic crystal slab structures in which C3 symmetry is maintained but the inversion symmetry is broken. We investigate the evolution of the Berry curvature from the honeycomb-lattice slab structure to the triangular-lattice photonic crystal slab and show that the triangular-lattice photonic crystals still support edge modes in a very wide photonic band gap. We find that the edge modes with zero Berry curvature can propagate with extremely low bending loss along the interface formed by the triangular-lattice photonic crystals

Fiber-Coupled Multiplexed Independent Ho:ZBLAN Waveguide Chip Lasers in a Single Substrate

A readily configurable and scalable 2 µm laser source with multi-channel/wavelength fiber output could be advantageous to 2 µm applications such as spectral-beam combination or fiber communications. We report the first experimental realization and characterization of a two-channel holmium-doped zirconium fluoride glass waveguide array laser pumped by a single thulium fiber laser at 1945 nm. Specific laser wavelengths are selected by fiber Bragg gratings (2076.7 nm and 2074.4 nm), and single channel powers of >100 mW are achieved. Design and assembly details, and considerations for future improvements are discussed, including the potential extension to and beyond a 12 channel source

Optical Chirality from Dark-Field Illumination of Planar Plasmonic Nanostructures

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

Broadband High-Efficiency Chiral Splitters and Holograms from Dielectric Nanoarc Metasurfaces

Simultaneous broadband and high efficiency merits of designer metasurfaces are currently attracting widespread attention in the field of nanophotonics. However, contemporary metasurfaces rarely achieve both advantages simultaneously. For the category of transmissive metadevices, plasmonic or conventional dielectric metasurfaces are viable for either broadband operation with relatively low efficiency or high efficiency at only a selection of wavelengths. To overcome this limitation, dielectric nanoarcs are proposed as a means to accomplish two advantages. Continuous nanoarcs support different electromagnetic resonant modes at localized areas for generating phase retardation. Meanwhile, the geometric nature of nanoarc curvature endows the nanoarcs with full phase coverage of 0–2π due to the Pancharatnam–Berry phase principle. Experimentally incorporated with the chiral‐detour phase principle, a few compelling functionalities are demonstrated, such as chiral beamsplitting, broadband holography, and helicity‐selective holography. The continuous nanoarc metasurfaces prevail over plasmonic or dielectric discretized building block strategies and the findings lead to novel designs of spin‐controllable metadevices.This work was partially supported by the National Natural Science Foundation of China (11604219, 61675136, U701661, 61427819, 61138003, and 61490712), the Leading talents of Guangdong province program (00201505), the Natural Science Foundation of Guangdong Province (2016A030312010), Science and Technology Innovation Commission of Shenzhen (KQTD2015071016560101), and Shenzhen Peacock Program (KQTD2017033011044403)