Simulation Studies on Quasi-Bound States in the Continuum Introduced by Out-of-Plane Symmetry Breaking in Dielectric Metasurfaces

Metasurfaces with high quality factor resonances can be fabricated by breaking the symmetry of the constituent resonators, thereby converting symmetry-protected dark states to quasi-bound states in the continuum.As the quality factor is inversely proportional to the degree of the asymmetry, high quality factor metasurfaces typically comprise fine-tuned resonators requiring state-of-the-art lithographic technologies to fabricate.In this study, a method is proposed to create quasi-bound states in the continuum in dielectric metasurfaces without high-resolution lithography.The results show that quasi-bound states in the continuum can be formed by introducing a non-vertical sidewall in an array of cube resonators, such that the resonator symmetry breaks in an out-of-plane direction.The proposed method enables fabrication by controlling the dry etching angle without extensive use of high-resolution lithography.Using full-wave electromagnetic simulations and multipole analyses, high quality factor resonances are observed in the proposed metasurface structure, the connections of which to the quasi-bound states in the continuum are clarified.Our work enables fabrication of high quality factor metasurfaces with low cost and high controllability, and is expected to greatly benefit the field of enhanced light-matter interactions in nanophotonics.