Radial and azimuthal quasi-bound states in the continuum for optical trapping

Abstract

Bound states in the continuum (BICs) have demonstrated significant potential for optical trapping due to their high Q-factor resonances and strong field enhancement. However, BICs must be extended in one or more directions, substantially increasing the device footprint, limiting their practical applications. While recent advancements have demonstrated azimuthal and radial quasi-BICs supported by aperiodic metasurfaces, their potential for trapping applications remains unexplored. In this work, we build upon these foundational models by introducing field enhancements and conducting a thorough investigation of their trapping performance. We propose an aperiodic dielectric nanotweezer platform that leverages quasi-BICs within an ultracompact footprint of approximately 7 μm², enabling efficient optical trapping of nanoparticles with low laser power and minimal heating effects. Our design features an aperiodic dielectric sectorial nanostructure with a central nanopillar, supporting two distinct quasi-BICs: azimuthal BICs, achieved by adjusting the angles between sector rods and excited by azimuthally polarized light, and radial BICs, realized by shortening one sector rod and excited with radially polarized light. Operating in the near-infrared spectrum, this system is especially suitable for manipulating biological specimens. This platform provides a compact on-chip optical tweezer device that outperforms existing nanotweezers, offering exceptional field enhancement, strong trapping stability, and broad adaptability, positioning it as a versatile and highly effective tool for advancing optical trapping technologies.