Strong magnetic field enhancement and magnetic Purcell effect in a dielectric disk-ring composite nanocavity
Yang Yang, Bofeng Zhu, Haitao Dai
Abstract
All-dielectric nanocavities with low dissipative absorption bring new opportunities for efficiently enhancing and confining the optical magnetic field. Recently, a high-index dielectric nanodisk with internal magnetic dipole (MD) mode has become a prominent candidate in accelerating the spontaneous decay of MD transitions in quantum emitters (known as the magnetic Purcell effect). In this paper, we numerically investigate a dielectric disk-ring composite nanocavity that is capable of achieving 1 order of magnitude stronger enhancement of the magnetic field than a single disk. Multipole decomposition analysis further reveals the ultra-high enhancement is attributed to the huge MD radiation originating from the near-field (radiative) coupling between the MD mode and the electric quadrupole (magnetic octupole). More importantly, the numerical results also indicate such a composite nanocavity supports a stronger Purcell effect than a single disk under the excitation of an MD emitter, which can be verified by theoretical calculations. Further simulation demonstrates the better tolerance of the composite nanocavity on larger hole dimensions, thereby reducing the experimental difficulties in both structure fabrication and emitter loading. In addition, the dependence of the Purcell factor on the dipole orientation is investigated, demonstrating the great compatibility of the composite nanocavity. This presented design could open a promising avenue beyond the individual disk cavity for light–matter interactions in the magneto-optical domain.