Enhancing Magnetic Dipole Emission by a Nano-Doughnut-Shaped Silicon Disk

High-index dielectric nanostructures support inherently strong magnetic dipole (MD) resonances at optical frequencies with minimal dissipative absorptions. They are promising candidates for MD radiation enhancement. Previous investigations, however, show that the maximum magnetic field enhancement is confined inside the nanostructure and therefore inaccessible to nearby MD emitters, limiting the achievable emission enhancement. In this paper, we design a nano-doughnut-shaped silicon disk, i.e., a disk with an open hole through its center. This way, the maximum magnetic field intensity is exposed and can be leveraged to fully enhance MD radiations. On the basis of numerical calculations, a record high enhancement factor of the radiative decay rate up to 350 has been achieved with minimal nonradiative losses. We further demonstrate the importance of spectral and spatial overlap of the MD emitter with the MD resonance in the silicon nanodisk in order to maximize the MD radiations. Our study opens new possibilities for MD emission enhancement and paves the road toward novel magnetic light-matter interactions.