Controllable Patterning of Metallic Photonic Crystals for Waveguide-Plasmon Interaction.

Waveguide-plasmon polaritons sustained in metallic photonic crystal slabs show fascinating properties, such as narrow bandwidth and ultrafast dynamics crucial for biosensing, light emitting, and ultrafast switching. However, the patterning of metallic photonic crystals using electron beam lithography is challenging in terms of high efficiency, large area coverage, and cost control. This paper describes a controllable patterning technique for the fabrication of an Ag grating structure on an indium-tin oxide (ITO) slab that enables strong photon-plasmon interaction to obtain waveguide-plasmon polaritons. The Ag grating consisting of self-assembled silver nanoparticles (NPs) exhibits polarization-independent properties for the excitation of the hybrid waveguide-plasmon mode. The Ag NP grating can also be annealed at high temperature to form a continuous nanoline grating that supports the hybrid waveguide-plasmon mode only under transverse magnetic (TM) polarization. We tuned the morphology and the periodicity of the Ag grating through the concentration of silver salt and the photoresist template, respectively, to manipulate the strong coupling between the plasmon and the waveguide modes of different orders.

Switchable Plasmonic Chirality for Light Modulation: From Near-Field to Far-Field Coupling.

This paper describes a quasi-planar chiral metamaterial of metal-insulator-metal (MIM) tetramer arrays that support multiplasmon modes from a hybridization scheme to achieve significant chiroptical responses with the largest circular dichroism (CD) value of 42%. The chiroptical responses can be actively switched on and off by tuning the field coupling regime from near field to far field through the insulator (or spacer) thickness. Numerical calculations demonstrate that near-field coupling of the hybridized plasmons on the stacked metallic tetramers governs the chiroptical responses at small insulator thickness (tSiO2 < 160 nm). In contrast, far-field coupling of the plasmon radiations dominates at large spacing (tSiO2 > 160 nm) as phase retardation plays a crucial role. The quasi-planar chiral metamaterial with tunable plasmonic chirality enables efficient light modulation for polarization conversion: from circular to elliptical/linear polarization.