Manipulation of resonances governed by Fabry-Perot bound states in the continuum

Bound states in the continuum (BICs) have emerged as research hotspots in optics and photonics, offering a new paradigm for achieving extreme field localization and enhancing light-matter interactions. Here, we establish for the first time the intrinsic evolution laws of Fabry-Perot bound states in the continuum (FP-BICs), revealing that the Q factor is inversely proportional to the square of phase/frequency detuning and to the nonradiative decay rate, enabling directional engineering of FP-BIC resonances. We propose an all-dielectric multilayer film metasurface to create an optical resonator and its perfectly mirrored counterpart, inducing FP-BICs and validating the conclusions. We experimentally demonstrated the evolution of the Q factor with frequency detuning, achieving a maximum Q factor of 610 in the visible. Our work offers novel insights into BICs, promising to inspire exotic phenomena and applications.