Ultra-low threshold optical bistability assisted by merging bound states in the continuum

We report the optical bistability (OB) working at the ultra-low threshold of intensity in Si metasurfaces of merging bound states in the continuum (BICs). The metasurfaces are designed by periodic Si nanorods, and the merged BICs are realized by modulating the height of Si nanorods. The merged BICs have been proven to effectively suppress the radiation loss and enhance the quality factors (Q factors) along with the local field. The intensity threshold for optical bistability can be down to the level of 100 W/cm². The results demonstrate that the Si nanorod structure, driven by merging BICs to achieve ultra-low-threshold OB, holds significant potential for applications in all-optical devices.