聚焦强度可调的高数值孔径的双焦点超透镜

基于超表面对光波的振幅、相位和偏振进行调控来实现聚焦与成像的超透镜受到广泛关注。设计了一种聚焦强度可调的高数值孔径的双焦点超透镜，并进行了理论分析和仿真验证。仿真结果表明，该超透镜能有效地将圆偏振入射光聚焦到半高宽为0.44λ的光斑上，对应的数值孔径高达0.95。此外，通过改变入射光的偏振态，可以灵活地调制两个焦点的相对强度，而不同于以往的双焦点超透镜需要对光强进行重新组合。更重要的是，当圆偏振光入射时，它的聚焦效率可达65%，可适用在0.8~1.2 THz的较宽频率范围和0°~20°的入射角内，同时该工作为多焦点超透镜的设计提供了重要思路，也将在多成像系统、光学层析成像技术等许多领域具有较高的应用价值。

High numerical aperture bifocal metalens with regulatory focusing intensity

The metalenses with focusing and imaging based on metasurfaces, which can manipulate the amplitude, phase, and polarization of light waves, have attracted enormous attentions. A high numerical aperture bifocal metalens with regulatory focusing intensity was designed, and both theoretical analysis and simulation verification were demonstrated. The simulation results reveal that the designed metalens can focus circularly polarized incident light efficiently to a spot of full width at half-maximum as small as ~0.44λ, and the corresponding numerical aperture reaches up to 0.95. Besides, the relative intensity of two focal points can be adjusted flexibly through changing the polarization states of the incident light, which is unlike previous bifocal metalenses with repatterned intensity. More importantly, when the circularly polarized light is incident, the focusing efficiency is both up to 65%, and it is available for a relatively broad frequency range from 0.8 to 1.2 THz and a wide incident angles of 0°-20°. This work provides an important idea for designing the multi-focal metalenses, and it will also have high application value in many fields such as multi-imaging system, optical tomography.