Glide symmetry, which is one kind of higher symmetry, is introduced in a special type of plasmonic metamaterial, the transmission lines (TLs) of spoof surface plasmon polaritons (SSPPs), in order to control the dispersion characteristics and modal fields of the SSPPs. We show that the glide-symmetric TL presents merged pass bands and mode degeneracy, which lead to broad working bandwidth and extremely low coupling between neighboring TLs. Dual-conductor SSPP TLs with and without glide symmetry are arranged in parallel as two channels with very deep subwavelength separation (e.g., λ₀ / 100 at 5 GHz) for the application of integrated circuits and systems. Mutual coupling between the hybrid channels is analyzed using coupled mode theory and characterized in terms of scattering parameters and near-field distributions. We demonstrate theoretically and experimentally that the hybrid TL array obtains significantly more suppressed crosstalk than the uniform array of two nonglide symmetric TLs. Hence, it is concluded that the glide symmetry can be adopted to flexibly design the propagation of SSPPs and benefit the development of highly compact plasmonic circuits.

模式是光纤光学中的基本概念，也是光纤激光器研究中最关注的问题之一。在一般的教材、文献中对模式的简并问题涉及较少，没有给出清晰、直观的物理图像。文中采用经典的电磁场理论，阐明了矢量模的简并度、标量模的简并度以及矢量模和标量模之间的简并关系。在弱导阶跃折射率光纤中，矢量模和标量模都是描述光场的正交完备基，矢量模[HE_1n^(o)、HE_1n^(e)]与标量模[LP_0n^(ye)、LP_0n^(xe)]描述的光场空间是2维的，矢量模[TE_0n、HE_2n^(o)、HE_2n^(e)、TM_0n]与标量模[LP_1n^(yo)、LP_1n^(ye)、LP_1n^(xo)、LP_1n^(xe)]描述的光场空间是4维的，矢量模[EH_{m-1, n}^(o)、EH_{m-1, n}^(e)、HE_{m+1, n}^(o)、HE_{m+1, n}^(e)]与标量模[LP_mn^(yo)、LP_mn^(ye)、LP_mn^(xo)、LP_mn^(xe)]描述的光场空间也是4维的。