Improving magnetic dipole emission by coupled silicon nanocuboid dimer

A coupled silicon nanocuboid dimer is employed to improve the magnetic dipole (MD) emission. Finite difference time domain (FDTD) simulations reveal that the nanocuboid dimer supports coupled magnetic resonance and confines a large magnetic field within the gap. The coupling and magnetic-field-enhancing capability are stronger than that of the nanosphere dimer due to the nonspherical symmetry of the nanocuboid. The MD resonance and the magnetic quadrupole (MQ) of the nanocuboid dimer are used to improve the emission of the MD emitter positioned within the gap. It is revealed that the MD resonance can lead to a large enhancement factor of 262 for the radiative decay rate at the wavelength of 653 nm. The enhancement factor is about 3.8 times that caused by the nanosphere dimer. The peak of the radiative decay rate can be tuned in a broad wavelength range by tailoring the structure parameters of the nanocuboid and an enhancement factor of over 230 is achieved at the long wavelength range. For a nanocuboid dimer with a larger size, the MQ resonance can lead to a higher enhancement factor of about 368 at the wavelength of 819 nm, which is nearly 1.5 times that caused by the nanosphere dimer.