Single-layer dielectric metasurface with giant chiroptical effects combining geometric and propagation phase

Planar chiral optics play an important role in modern optical detections, for example, imaging systems. Here, we extend the scheme to design planar chiral devices by combining both the geometric phase and propagation phase. Both the propagation and geometric phase can be used to modulate wavefront for the single-layer chiral metasurface. The supercells, containing interference effect among adjacent building blocks inside, are constructed to achieve a strong chiral effect. The circular dichroism in transmission of metasurface with periodic arrangement of supercells can reach as high as 0.937 at mid-infrared range. Meanwhile, the supercells on metasurface exhibit the ability of geometric and propagation phase modulation, which is employed to realize chiral metalenses supporting spin-selective focusing effects. We believe that the proposed scheme could be readily extended for designing compact and miniaturized chiral devices and promote their practical applications.