Three-dimensional vector wave bound states in a continuum

Recently, bound states for a certain polarized electromagnetic wave have been demonstrated to exist within the radiation continuum in large periodic arrays and open resonators, analogous with embedded eigenvalues in certain quantum systems. Here, we demonstrate that it may be possible to induce three-dimensional photonic embedded eigenvalues for vector waves with both polarizations in a subwavelength open scattering system. These bound states have infinitely large lifetimes, which are very sensitive to the absorption and fluctuation of the structure. Although the effect of absorption on the bound states in the continuum (BICs) is strong, it can always be overcome by introducing optical gains in the systems. However, to obtain the BICs, precise control of the aspect ratio of the structure is needed.