一种表面等离子体激元定向耦合器的传输特性

Propagation Properties of a Surface Plasmon Polariton Directional Coupler

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 kind of surface plasmon polariton（SPP） directional coupler in which metal strip between the two adjacent waveguides is thinner than the metal film is simulated by using three dimensional full-vectorial finite difference time-domain（FDTD） method.The distributions of electromagnetic field and longitudinal energy flux density when only fundamental mode propagates in waveguides are analysed,and the dependences of coupling length and maximum transfer power on the height of metal strip are discussed.Results show that the energy flux density along the propagation direction distributions mainly in the part near the metal strip,which is beneficial to increase the coupling strength.Also,the efficient decrease of coupling length in directional coupler can be achieved by reducing the height of metal strip between waveguides.This sub-wavelength of directional coupler can be applicable for the optical integrated circuit based on surface plasmon polaritons.