Design of Metasurface Lens with Two Focal Spots Based on Polarization Response

A focusing lense with two focal spots based on dielectric metasurface was designed which can extend the focus axially. The device modulates the propagation phase and the geometric phase at the same time and realizes the independent control of a group of orthogonal polarized incident light by varying the aspect ratio and the rotation angle of the titanium dioxide pillars. The designed metasurface focuses the left-handed and right-handed circularly polarized light at contiguous positions to extend the focus axially. We extend the length of focus twice as initial value at 650 nm wavelength and maintain the lateral width of the focus in the meantime. The optimization of the focus shape and the switch of focus position with different focal lengths can be realized by adjusting the incident light into an elliptically polarized light.