Multiband enhancement of magnetic dipole emission with tapered hollow hyperbolic metamaterials.

Based on a single resonance, nanostructures often provide narrowband enhancement for magnetic dipole emissions. Here, tapered hollow hyperbolic metamaterial is designed in order to produce a multiband emission enhancement. Specifically, a series of coaxial magnetic hot spots is excited inside the structure in five discrete bands. Meanwhile, we demonstrate that the emission enhancement can be achieved at both multiple wavelengths and multiple spatial positions in one single device. An enhancement factor of radiative decay rate up to 694 is obtained. Results of this paper might open new possibilities for nanostructures to achieve multiband light emission enhancement in the magneto-optical domain.