High-efficiency directional excitation of spoof surface plasmons by periodic scattering cylinders

Directional surface plasmon polariton scattering using single magnetic nanoparticles

Directional surface plasmon polaritons (SPPs) are expected to promote the energy efficiency of plasmonic devices, via limiting the energy in a given spatial domain. The directional scattering of dielectric nanoparticles induced by the interference between electric and magnetic responses presents a potential candidate for directional SPPs. Magnetic nanoparticles can introduce permeability as an extra manipulation, whose directional scattered SPPs have not been investigated yet. In this work, we demonstrated the directional scattered SPPs by using single magnetic nanoparticles via simulation and experiment. By increasing the permeability and particle size, the high-order TEM modes are excited inside the particle and induce more forward directional SPPs. It indicated that the particle size manifests larger tuning range compared with the permeability. Experimentally, the maximum forward-to-backward (F-to-B) SPP scattering intensity ratio of 118.52:1 is visualized by using a single 1 μm Fe3O4 magnetic nanoparticle. The directional scattered SPPs of magnetic nanoparticles are hopeful to improve the efficiency of plasmonic devices and pave the way for plasmonic circuits on-chip.

Efficient Meta-couplers Squeezing Propagating Light into On-Chip Subwavelength Devices in a Controllable Way

On-chip photonic systems play crucial roles in nanoscience and nanoapplications, but coupling external light to these subwavelength devices is challenging due to a large mode mismatch. Here, we establish a new scheme for realizing highly miniaturized couplers for efficiently exciting on-chip photonic devices in a controllable way. Relying on both resonant and Pancharatnam-Berry mechanisms, our meta-device can couple circularly polarized light to a surface plasmon, which is then focused into a spot placed with a target on-chip device. We experimentally demonstrate two meta-couplers. The first can excite an on-chip waveguide (with a 0.1λ × 0.2λ cross section) with an absolute efficiency of 51%, while the second can achieve incident spin-selective excitation of a dual-waveguide system. Background-free excitation of a gap-plasmon nanocavity with the local field enhanced by >1000 times is numerically demonstrated. Such a scheme connects efficiently propagating light in free space and localized fields in on-chip devices, being highly favored in many integration-optics applications.