Enabling infinite Q factors in absorbing optical systems

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

Automated summary

Resonant optical structures are widely used in science and technology, but their Q factors can be reduced if some parts exhibit optical absorption. We propose a method to create a nonradiating and absorption-free bound state in the continuum (BIC) by coupling a lossy mode of the structure to two independent lossless modes. This BIC has theoretically unlimited Q factors despite interaction with an absorbing structure. Using this mechanism, we design a plasmonic metasurface with Q factors close to 10^7 in the visible spectral range. This mechanism can be applied to engineer ultrahigh-Q resonances in various systems containing absorbing structures.