High-Q modes in a single dielectric nonspherical nanocavity

High index dielectric nanostructures support both electric and magnetic multipole resonances. In real applications, it is desirable to achieve high-quality optical resonances to have a high-Q factor within a small volume of a material. Here, we demonstrate the high-Q factor resonant modes in a single nonspherical dielectric nanocavity (i.e. rectangular nanowire, cuboid, and disk) by exploring quasi-bound states in the continuum. We find that the high-Q modes only occur at a specific size aspect ratio, around which avoided crossing (or crossing) feature appears for pair modes. The Q factor can be up to 2.31×104 for square nanowire (n=4) with a/λ0<1. Multipole analysis on the high Q eigenmode indicates that radiation is significantly suppressed in the limited eigenchannels. High Q modes are verified experimentally via scattering spectrum.