Enabling infinite <i>Q</i> factors in absorbing optical systems

Abstract Resonant optical structures have widespread applications in science and technology. However, their quality ( Q ) factors can be significantly deteriorated, if some of parts exhibit absorption. Here, we show that by coupling a lossy mode such structure to two independent lossless modes, one create nonradiating absorption-free bound state the continuum (BIC). The factor BIC is theoretically unlimited despite interaction with an absorbing structure. We use this mechanism design plasmonic metasurface are close 10 7 visible spectral range. proposed general used engineer ultrahigh- resonances various systems containing structures.