Unidirectional excitation of UV surface plasmons by asymmetric nano-slit cavity assisted with a nano-grating

Ultraviolet surface plasmon polaritons (UV SPPs) have important and extensive potential applications in SPPs nanolithography, SERS, LEDs, solar cells, photocatalysis, and so on. Recently, more and more attention has been paid to extend plasmonic properties from the visible and near-IR band into the ultraviolet range. However, the low efficiency to generate UV plasma is an enormous challenge and unidirectional excitation of SPPs is considered as a reliable way to solve the problem. Here we theoretically propose a structure with an asymmetric nano-slit cavity that serves as an efficient unidirectional coupler for deep UV plasmons, especially for the wavelength of 248nm, which is a typical light source used in the SPPs nanolithography. The theoretical results based on FDTD algorithm show that by optimally designing the asymmetric nano-slit cavity the extinction ratio can reach 16.8 dB and can be further increased to 28.0 dB when assisted by a nano grating. Additionally the direction of the proposed unidirectional excitation is controllable by adjusting the length of nano-slit cavity.