Index-near-zero modes in Si photonic crystal supported by accidental bound states in the continuum

Epsilon-near-zero (ENZ) materials have attracted attention for more than a decade. With a lot of advances in their functionalization it also has come an understanding that most of such natural materials exhibit high intrinsic losses at optical frequencies. Therefore, as an alternative, index-near-zero (INZ) materials are currently being investigated. The use of nanostructured dielectric materials with specific mode profiles, which effectively provides very small modal indices, is considered a potential solution. We report on such system, which has been designed, fabricated and characterized recently. Quasi-bound states in the continuum are involved to minimize the radiative losses of INZ modes.