利用三维全矢量时域有限差分法(FDTD)数值模拟了一种波导间隔金属条高度小于金属层厚度的表面等离子体激元(SPP)定向耦合器,并分析了其在基模传输时的模式场分布和能流密度分布,讨论了耦合长度、最大转移功率与间隔金属条高度的变化关系。结果表明,波导内沿纵向的能流密度在靠近间隔金属条部分的强度更大,有助于提高波导间耦合效率,并且当减小间隔金属条的高度时可以有效缩短定向耦合器耦合长度。这种亚波长定向耦合器结构可以应用在基于表面等离子体激元的集成光路中。 A three-dimensional full-vector finite-difference time-domain (FDTD) method was used to simulate a surface plasmon polariton (SPP) directional coupler whose waveguide metal strip height was less than that of the metal layer. The mode Field distribution and energy flux density distribution, the relationship between coupling length, maximum transfer power and the height of spacer metal strip is discussed. The results show that the energy density in the longitudinal direction of the waveguide is more intense near the spacers and helps to improve the coupling efficiency between the waveguides and effectively shorten the length of the directional coupler when the height of the spacers is reduced. This sub-wavelength directional coupler structure can be used in the surface plasmon based integrated optical path.