Robust chirality through merging BICs

Robust chirality is demonstrated by exploiting the merging of multiple accidental bound states in the continuum (BICs). This mechanism simultaneously sustains ultrahigh-quality factor Q resonances and strong chiroptical responses across a wide region of momentum space, achieving near-perfect circular dichroism (~0.99) and an ultrahigh-Q value (~10⁴) in a planar dielectric platform.