Enabling low Threshold Laser Through an Asymmetric Tetramer Metasurface Harnessing Polarization‐Independent Quasi‐BICs

Abstract It is proposed and numerically demonstrated a novel strategy to achieve lasing generation from a dual‐band symmetry‐protected bound states in the continuum (BICs) based on a nanodisk tetramer metasurface. The method involves breaking the in‐plane symmetry of the metasurface unit cell by the simple introduction of air holes in the tetramers. The numerical results show that this easy to fabricate solution enables the support of dual‐band BICs in the telecom‐band range, with these modes evolving into quasi‐BICs with remarkably high quality factors. Furthermore, the resulting device exhibits the unique characteristic of being polarization‐independent across all viewing angles. Finally, the adopted gain medium provides sufficient optical gain to compensate the quasi‐BIC mode losses, enabling two mode lasing with ultra‐low pump threshold and very narrow optical linewidth. This work paves the way for polarization‐independent metasurfaces with multiple lasing resonances, holding the potential to transform areas such as low‐threshold lasing and biosensing by delivering improved performance and broader capabilities.