Bound states in the continuum based on controlling the phase difference in dielectric corrugated structures

Bound states in the continuum (BICs) with an infinite quality factor ($Q$ factor) and lifetime are demonstrated as far-field polarization singularities in momentum space. Unidirectional guided resonances (UGRs) are only a $V$ point (vortex polarization singularity) in the upper or lower half space to block the radiation channel. In photonic systems, the evolution between BICs and UGRs can be achieved by adjusting the structure parameters. However, the coexistence of BICs and UGRs has not been realized so far. Here, we propose a dielectric corrugated structure and find that the far-field radiation of the structure can be controlled by changing the phase difference between the upper and lower surfaces. The coexistence of BICs and UGRs can be achieved at a specified phase difference. Interestingly, as the $V$ points evolve with the phase difference, a high $Q$ factor platform is realized. Our results provide a means to achieve the high $Q$ factor platform and the coexistence of BICs and UGRs in momentum space, which promotes greatly the study of far-field radiation manipulation and high $Q$ factor resonance.