All-dielectric metasurfaces: generating optical vortices through quasi-bound states in the continuum and thermal tunability

When the in-plane inversion symmetry is broken, it leads to intercoupling between free space and the eigenmodes, thereby establishing a radiation channel for bound states in the continuum (BICs). Consequently, BIC evolve into quasi-BIC (q-BICs), which are protected by symmetry. The q-BIC then forms a Pancharatnam-Berry phase upon induction of its topological phase by a Gaussian circularly polarized wave. This process results in an optical vortex (OV) with a topological charge l = +2. Creation of this OV does not require an exact geometric center, thereby addressing the challenge of beam alignment and obviating the need for a precise unit design. Considering this, the designed metasurface holds extensive potential for future applications in nonlinear optics, imaging, sensing, and measurement.