In this paper, we propose a novel sub-wavelength plasma structure that can effectively enhance surface plasmon resonance (SPR) to achieve a significant local field. On the basis of a plasma ring structure, we add a slit and two thin plasma layers, working as a metal-insulator-metal (MIM) waveguide at a specific incident wave frequency and generate the Fabry-Perot resonance (FPR). The structure thus couples the incident wave energy to the vicinity of the slit and intensifies the SPR inside the plasma ring. In addition, we also find the coupling and competing between SPR and FPR. For the coupling mode, the average field enhancement in the ring is up to a factor of 9.7. Moreover, the optimized thickness of the plasma layer is much thinner than the skin depth of the plasma to ensure the incident wave easily entering the MIM waveguide. We further calculate the dispersion relationship of surface plasmon polaritons in the waveguide cavity. The simulation results and theoretical dispersion function are in good agreements.

在本文中，我们提出了一种新颖的亚波长等离子体结构，可以有效地增强表面等离子体激元共振（SPR），以实现显着的局部场。在等离子环结构的基础上，我们添加了一个狭缝和两个薄的等离子层，它们以特定的入射波频率充当金属-绝缘体-金属（MIM）波导，并产生法布里-珀罗共振（FPR）。因此，该结构将入射波能量耦合到狭缝附近，并增强了等离子体环内部的SPR。此外，我们还发现了SPR和FPR之间的耦合和竞争。对于耦合模式，环中的平均场增强高达9.7倍。此外，等离子体层的优化厚度比等离子体的趋肤深度薄得多，以确保入射波容易进入MIM波导。我们进一步计算了表面等离激元极化子在波导腔中的色散关系。仿真结果与理论色散函数吻合良好。