Enabling low threshold laser through an asymmetric tetramer metasurface harnessing polarization-independent quasi-BICs

We propose and numerically demonstrate a novel strategy to achieve dual-band symmetry-protected bound states in the continuum (BICs) based on a nanodisk tetramer metasurface for lasing generation. The method involves breaking the in-plane symmetry along the diagonal of the metasurface unit cell by introducing air holes in the tetramers. Through our simulations, we show that this flexible approach enables the support of dual-band BICs in the telecom-band range, with these modes evolving into quasi-BICs with remarkably high quality factors by breaking the symmetry of the system. Furthermore, the ultracompact device exhibits the unique characteristic of being polarization-independent across all viewing angles. Finally, the optically pumped 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 in the telecom-band range. Our adaptable device paves the way for polarization-insensitive metasurfaces with multiple lasing resonances. This innovation holds the potential to transform areas like low-threshold lasing and biosensing by delivering improved performance and broader capabilities.