Rotation-enabled efficient manipulation of bound states in the continuum and unidirectional guided resonances

Bound states in the continuum (BICs), due to their unique properties to confine light, have recently been studied intensively in dielectric gratings. To manipulate BICs, several methods are commonly used, such as using a reshaped resonant element, two asymmetric elements, misaligned stacked gratings, and so on, but more tuning degrees of freedom are still in great demand. We here demonstrate an emerging degree of freedom to achieve BIC manipulation, i.e., rotation. By rotating the structural unit, the original three BICs are broken, and then one symmetry-protected BIC at Γ point and one accidental BIC at off- Γ point re-emerge both at Γ point. By tracking their topological charges, they are shown to exchange their band branches. Moreover, by rotation, these two BICs can be evolved into two unidirectional guided resonances (UGRs). Our work paves the way toward even more abundant and powerful light manipulation based on BICs and topological optics.