SPPs directional excitation of linearly polarized light based on catenary nanoparticle metasurface

Surface plasmon polaritons (SPPs) directional excitation is the basis for the development of on-chip integrated photonic systems, such as the super-resolution imaging, the nano lithography, and the high sensitivity biosensors. It is difficult for traditional directional structures, such as prisms, nano slits and grooves to satisfy the accurate phase-matching condition required for SPPs excitation, resulting in an unsatisfactory coupling efficiency, a low extinction ratio, and high loss and noise. In recent years, the directional excitation of surface plasmon polaritons based on the catenary metasurface began to be valued because of the continuous and linear geometric phase control ability. However, the research of SPPs directional excitation with linearly polarized light is less than that of circularly polarized light. In this paper, all excitation is explained according to the multi-level scattering theory and the Huygens-Fresnel principle. The simulation results show that at the resonance wavelength (836 nm), the SPPs directional excitation is effectively achieved due to the stronger electric dipole excited by SPPs resonances. At the same time, in the effective bandwidth range (820 nm~870 nm) of unit catenary nanoparticle, the electric dipole scattering intensity and spectral extinction ratio curve both show the trend of increasing first and then decreasing. Therefore, there is a positive correlation between the electric dipole scattering intensity and spectral extinction ratio curve. The above analysis shows that the dipole intensity is the main factor affecting the directional extinction ratio. The designed directional excitation of surface plasmon polaritons with linearly polarized light based on the catenary nanoparticle metasurface is effective. The peak extinction ratio is up to 27 dB (corresponding to the incident wavelength of 820 nm), and the bandwidth above 10 dB is about 47 nm (798 nm~845 nm). Therefore, these results are helpful for the research and development of the catenary multifunctional devices which has great potential in the design of SPP directional excitation devices. Besides, it is also a planar integrated device, which can provide new ideas for chip-level photonic device or system design. Moreover, the method in this paper is also suitable for circularly polarized light, therefore it can be referenced in the design of other multi-functional integrated photonic devices such as multi-directional beam splitters and polarization detectors.