Engineering ultra-high <i>Q</i> multiple quasi-bound states in the continuum via an all-dielectric metagrating: polarization and incident angle effects in the visible range

This study presents the engineering of multiple quasi-bound states in the continuum (QBICs) with ultra-high quality-factors ( Q ) by precisely tuning geometrical parameters in a simple-to-fabricate, one-dimensional (1-D) all-dielectric metagrating (ADM). The ADM consists of silicon oxynitride (SiON) metagrating on a silica (SiO 2 ) substrate, operating in the visible spectrum. We simulate the occurrence of multiple accidental QBICs (A-QBICs) at normal incidence and both symmetry-protected QBICs (SP-QBICs) and A-QBICs at oblique angles of incidence, for both transverse electric (TE) and transverse magnetic (TM) polarizations. We have also analyzed the nature of the engineered QBICs in reciprocal space and their mode profiles. The simulated QBICs exhibit an ultra-high Q (4.5×10 3 and 1.7×10 5 for TE, and 3.7×10 4 and 1.3×10 3 for TM), driven by toroidal dipoles and magnetic quadrupole resonances. The simple 1-D ADM design overcomes fabrication challenges associated with high- Q resonators. These multiple ultra-high Q QBICs, occurring at distinct wavelengths, are simultaneously supported by the same metagrating, offering significant tunability for multi-wavelength applications in the visible range. These findings highlight the potential for scalable, easy-to-fabricate ultra-high Q optical devices such as optical sensors, tunable lasers, and advanced fluorescence imaging systems for applications in the visible spectrum.