Polarization-dependent metalens with flexible and steerable bifocal spots

Abstract

Lenses are an important part of modern optical systems. We propose metalenses with bifocal spots, which realizes the beam focusing with controllable intensity ratio and free deflection of the bifocal spots. The metalens consists of an array of titanium dioxide (TiO2) nanopillars, which can provide two different propagation phases for x-linear polarization (XLP) and y-linear polarization (YLP) incidence, respectively. Therefore, by precisely choosing the size of the nanopillars, it is possible to produce two different focal spots for the two orthogonal input polarized light. And the intensity of the two focal points can be adjusted by changing the polarization angle of the incident light. Superimposing the initial phase distribution of the metalens and the phase distribution of the beam deflector metasurface enables multi-dimensional adjustment of the two focal points and realizes the free deflection characteristics of the metalens. The deflection angle of the focal spot is close to the theoretical deflection angle. In addition, multiple superposition can produce more deflection angles or deflect the focus to a two-dimensional plane. The method of controlling the targeting phase of the metalens by superimposing additional phases gives us the ability to fully manipulate the phase and wavefront of the metalens, providing a new idea for the continuous angle change of future optical lenses.

Keywords

• Bifocal metalens
• Polarization dependent
• Steerable position of focal spots
• All-dielectric metasurfaces
• Integrated optics