Unidirectional excitation of plasmonic waves via a multilayered metal-dielectric-metal Huygens' nanoantenna

Efficient unidirectional SPP launcher: coupling the SPP to a smooth surface for propagation

We propose a unidirectional surface plasmon polariton (SPP) launcher with high coupling efficiency and long propagation length. The structure consists of a metallic slanted grating and a metal film that are separated by a SiO₂ layer on a quartz substrate. By inserting the SiO₂ layer, strong interaction between the metal grating and metal film can significantly increase the conversion of incident light into SPPs. Meanwhile, due to the characteristics of the smooth interface between metal film and substrate, the dissipation of SPP originating from the propagation process will be remarkably reduced. Numerical simulations show that this structure with 11 grating periods will obtain high contrast and efficiency of launching. Compared with the rough metal-quartz interface, the smooth one can improve the efficiency of light conversion to SPPs by more than 22.6% and extend the propagating distance by approximately 158%.

Efficient planar plasmonic directional launching of linearly polarized light in a catenary metasurface

Efficient directional excitation of planar surface plasmon polaritons (SPPs) has important and wide applications in micro-nano photonic technology. Recently, by using the geometric phase and spin-orbit interaction, catenary structures have been applied to the directional control of SPPs and showed excellent performance. However, due to the need to use the chirality of the subwavelength catenary apertures, the previously studied systems were only suitable for circularly polarized light. Here, based on a catenary metasurface we theoretically design and experimentally demonstrate a SPP directional launcher used for linearly polarized light. The numerical calculation results show that the directional extinction ratio reaches up to 35 dB under the normal incidence of p-polarized light at 750 nm which is 5 dB higher than the maximum extinction ratio in the existing results as we know. The experimental results show that the resonant wavelength position, bandwidth and extinction ratio change trend well match the theoretical results. The physical mechanism is analyzed and it is found that the asymmetric quadrupole mode is the key factor leading to the directional SPPs which is completely different from the geometric phase modulation mechanism to excite the directional SPPs of circularly polarized light in the catenary metasurface. These principles and methods could open new doors for future chip-level photonic device or system design such as multi-directional beam splitters and polarization detectors.