High-Q Quasi-BIC Assisted Photonic Crystal Slab Nanotweezers

Photonic crystal slabs are periodic nanostructures designed to manipulate electromagnetic waves that offer a versatile platform for a wide range of applications in nanophotonics. This paper presents a thin photonic crystal slab made of Si3N4 for optical trapping of biological nanoparticles. By breaking the symmetry of the slab, a quasi-bound state in the continuum (quasi-BIC) is obtained at a near-visible wavelength of ~ 785 nm with a high quality factor (Q-factor) of ~ 3800. At this wavelength, a high electric field enhancement of ~ 63 is obtained at four different locations in the slab. Using the high field enhancement, stable trapping of extracellular vesicles (EVs) with a diameter of 50 nm is numerically investigated. The influence of varying the geometric parameters of the slab on the quasi-BIC characteristics is also studied. The proposed photonic crystal slab can be used as nanotweezers for simultaneous trapping of multiple nanoparticles with a low input power.