Bound states in the continuum in a waveguide structure covered by a two-dimensional square array of gold nanodisks

A bound state in the continuum (BIC) is a concept of a wave phenomenon that remains confined even though it coexists with a continuous radiative spectrum. In photonics, such states are promising for the enhancement of the light-matter interaction. In this work, we study the optical properties of the a-Si0.65C0.35:H-based planar waveguide structure covered by a two-dimensional array of gold nanodisks. To obtain BICs, we use a square lattice of nanodisks, which has one of the highest degrees of symmetry. The lattice provides light coupling to both TE and TM guided modes, while the single nanodisk supports localized plasmon resonance. We show that the structure possesses different types of BICs which are the result of the interaction of guided modes and single-particle resonances.