Strongly coupled phonon polaritons in patterned polar dielectric nano-resonators give rise to the formation of hybridized energy states with intriguing properties. However, direct observation of mode coupling in these periodic nanostructures is still challenging for momentum-matching-required far-field spectroscopies. Here, we explore the near-field response of strong coupling between propagating and localized polariton modes sustained in SiC phonon polaritonic crystals (PhPCs) to reveal the evolution of Rabi splittings with the change of lattice constant in the near-field perspective. The near-field nano-spectra of PhPCs show distinct Rabi splitting near the forbidden bands of ∼16 cm−1 in the band structures. In particular, an exotic three-polariton-coupling effect is observed with three splitting peaks in the nano-spectra induced by the interaction between local monopolar modes in nano-pillars and zone-folded phonon polaritons. Furthermore, sharp dips indicating weak near-field scatterings appear in nano-spectra at the intrinsic frequencies of the monopolar modes with strong local-field enhancement, which are estimated to be bright scattering peaks intuitively. These results would inspire the dispersion engineering and characterization of coupled phononic nano-resonators for diverse nanophotonic applications.

中文翻译：

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声子极化晶体中强模式耦合的近场纳米光谱学

图案化极性介电纳米谐振器中的强耦合声子极化激元会形成具有有趣特性的杂化能态。然而，直接观察这些周期性纳米结构中的模式耦合对于动量匹配所需的远场光谱学仍然具有挑战性。在这里，我们探索了在 SiC 声子极化子晶体 (PhPC) 中持续的传播和局部极化子模式之间强耦合的近场响应，以揭示 Rabi 分裂随着近场视角中晶格常数的变化而演变。PhPC 的近场纳米光谱在~16 cm 的禁带附近显示出明显的 Rabi 分裂−1在能带结构中。特别是，观察到奇特的三极化子耦合效应，纳米光谱中的三个分裂峰是由纳米柱中的局部单极模式与区域折叠声子极化子之间的相互作用引起的。此外，在具有强局部场增强的单极模式的固有频率处，纳米光谱中出现表明弱近场散射的急剧下降，直观地估计是明亮的散射峰。这些结果将激发用于各种纳米光子应用的耦合声子纳米谐振器的色散工程和表征。