Observation of hybridized dark and bright modes in coupled dark resonators

Mode coupling offers a degree of freedom for tailoring optical responses in plasmonic nanostructures, which is beneficial for both fundamental and applied studies in optoelectronics. While a wealth of mode hybridization phenomena were reported for interactions between two bright modes or a bright mode and a dark mode, the coupling between dark modes remains underexplored. Here, we report on the coupling properties of two dark modes in plasmonic metamaterials. In our fabricated dual-stripe resonators made of metal–insulator–metal (MIM) layers, the coupling of dark second-order magnetic resonances leads to both hybridized bright mode and dark mode, whose quality (Q) factors are improved by a factor of approximately 2 compared to the uncoupled mode in single-stripe resonators in measurement. Polarization-selective excitations of the hybridized bright mode and dark mode are also demonstrated and are explained with both near-field and far-field mode properties. By varying the coupling strength of the MIM resonators, critical coupling of the hybridized mode can be achievable, allowing a flexible control over the absorption efficiency and the Q factor. Our findings provide new insights into dark mode coupling properties, which laid a foundation for hybridized mode applications in sensing, thermal engineering, and nanophotonic devices.