Modulation of optical force by adjusting the distance between three-layer photonic crystal slabs

Optical forces induced by polarization singularities from photonic crystal slabs (PCSs) have gained widely attention in recent years. To enhance the degree of freedom in controlling far-field optical forces, we propose and design a three-layer PCSs structure that simultaneously possesses multiple optical forces with reconfigurability. By modulating the interlayer spacing, the coupling strength between the slabs is regulated, resulting in a band transition from the nodal rings to the nodal ridge, which facilitates the generation of dual polarization vortices. These dual polarization vortices induce multiple phase singularities at their boundaries, leading to multiple optical force singularities, offering the possibility of capturing and dispersing nanoparticles. Interestingly, tuning the spacing among the slabs can transform the converging force into the diverging force at the center, therefore achieving particle screening. This work not only expands the application of nodal ridges to optical force in photonic structures but also provides a feasible approach for the generation of double-ring vortex beam in the nano-optics field.