Guiding light through optical bound states in the continuum for ultrahigh-Q microresonators

Light is usually confined in photonic structures with a band gap or relatively high refractive index for broad scientific and technical applications. Here, a light confinement mechanism is proposed based on the photonic bound state in the continuum (BIC). In a low-refractive-index waveguide on a high-refractive-index thin membrane, optical dissipation is forbidden because of the destructive interference of various leakage channels. The BIC-based low-mode-area waveguide and high-Q microresonator can be used to enhance light-matter interaction for laser, nonlinear optical and quantum optical applications. For example, a polymer structure on a diamond membrane shows excellent optical performance that can be achieved with large fabrication tolerance. It can induce strong coupling between photons and the nitrogen-vacancy center in diamond for scalable quantum information processors and networks.