领结形中空表面等离子体波导的传输特性

摘要

A kind of surface plasmonic waveguide with a bowtie shaped air core was designed.The dependence of distribution of longitudinal energy flux density, effective index and propagation length of the fundamental mode supported by this waveguide on geometrical parameters and working wavelength were analyzed using the finite-difference frequency-domain (FDFD) method.Results show that the longitudinal energy flux density distributes mainly in the center region which is formed by the top and the bottom ridge.The effective index and propagation length of the fundamental mode can be adjusted by the geometric parameters as well as the working wavelength.At a given working wavelength, the effective index decreases as the radius of ridge increases, meanwhile propagation length and mode area of the fundamental mode increase as radius of ridge increases.The geometric parameter of radius of circles at four corner can affect the propagation properties slightly.The radius of sectors on both sides can effect propagation properties obviously.With given geometric parameters, relative to the case of λ = 705.0 nm, in the case of larger λ, the area of field distribution is larger, and the size of the contact area of field and metallic surface is also larger, then the interaction of field and silver is weaker, and the effective index becomes smaller, so the propagation length becomes larger.The possibility of applying this kind of surface plasmonic waveguide to the field of sensors was discussed.%设计了一种领结形中空表面等离子体波导.采用频域有限差分法,对这种波导所支持的基模的能流密度分布、有效折射率、传播长度和模式面积随几何结构参数和工作波长的依赖关系进行了分析.结果表明,沿纵向的能流主要分布在两个上下突起所形成的中间区域.通过调整几何参数及工作波长,可以调节模式的有效折射率、传播长度和模式面积-在工作波长确定的条件下,有效折射率随突起半径的增大呈减小趋势,而传播长度和模式面积则随着突起半径的增大呈增大趋势,四个角上的圆弧半径对波导的传输特性有微调作用,左右扇形区域的半径对波导的.传输特性有较明显的调节作用.在几何参数确定的条件下,相对于工作波长705.0 nm的情形来说,工作波长较大时,场的分布范围较大,场与金属表面的接触面积较大,场与金属银的相互作用较弱,有效折射率就较小,传播距离也就较长.最后,讨论了这种中空表面等离子体波导在传感器领域应用的可能性.