设计了一种由双平行圆柱形纳米棒构成的金属-介质-金属（MDM）型等离子体波导, 采用时域有限差分方法（FDTD）分析了波导结构的传输特性。当光波垂直主轴入射时, 电磁场被很好地局限在两纳米棒所形成的中间区域以及介质层中, 从而在该波导中能够有效地耦合电磁场能量。在工作波长为1 550 nm的情况下, 随着内层金属芯半径的增大, 有效折射率减小, 传播距离增大; 而中间介质层厚度增大时, 有效折射率增大, 传播距离减小。当外层金属壳厚为20 nm时, 电场可以很好地被限制在纳米棒的介质层内。上述结果表明: 通过调整波导结构的几何参数可以显著提高金属纳米棒的场限制, 降低波导本身的损耗, 使波导的有效折射率和传播长度达到最优化。这种等离子体波导能够实现亚波长的光限制, 可以应用于光子器件集成和传感器领域。

A kind of metal-dielectric-metal (MDM) plasmonic waveguide with double parallel cylindrical nanorods was investigated. The propagation properties of the waveguide structure were analyzed using the finite-difference time-domain (FDTD) method. The results show that the electromagnetic field is well confined to the dielectric layer and the intermediate region formed by the two cylindrical nanorods when the incident light is perpendicular to the major axis, so the filed can be efficiently coupled into the waveguide. At the working wavelength λ=1 550 nm, the effective index decreases with the increase of the inner radius r1, meanwhile the propagation length increases as the inner radius r1 increases. However, in the case of larger d, the effective index becomes large, and the propagation length becomes short. In addition, the field can be predominantly confined within the dielectric layer in the case of g=20 nm. In short, adjusting the geometrical parameters can significantly improve the confinement of the SPPs fields and reduce the losses of the waveguide, so that the effective refractive index and propagation length of the waveguide can be optimized. Subwavelength optical confinement can be achieved in this kind of plasmonic waveguide, which will be applied to the fields of photonic device integration and sensors.