Effect of substrate on optical bound states in the continuum in 1D photonic structures

Optical bound stales in the continuum (BIC) are localized states with energy lying above the light line and having infinite lifetime. Any losses taking place in real systems result in transformation of the bound states into resonant states with finite lifetime. In this work, we analyze properties of BIC in CMOS-compatible one-dimensional photonic structure based on silicon on-insulator wafer at telecommunication wavelengths, where the absorption of silicon is negligible. We reveal that a high-index substrate could destroy both off-Gamma BIC and in-plane symmetry protected at-Gamma BIC turning them into resonant states due to leakage into the diffraction channels opening in the substrate.