Fan Chun-Yuan, Tang Pei-Yu, Su Vin-Cent, Cheng Ko-Ting, Teng Chia-Yu, Tsai Ming-Yu, Chiang Chia-Hung, Xu Kai-Lun, Su Guo-Dung J
Opt Lett. 2023 Sep 1;48(17):4452-4455. doi: 10.1364/OL.497776.
This Letter describes the design procedure and process optimization of the electrically bifocal metalens. In our design, horizontal and vertical polarization is manipulated by applying a suitable voltage to a twisted nematic liquid crystal (TN-LC) cell. Each nanostructure is designed to be a rectangular prism, making different polarizations of light experience various phase delays, thus causing bi-focus. We selected lithographical methods to fabricate our metalens because of the minimum physical size, which can be as small as 50 nm, and the maximum aspect ratio, which is as high as 15. Furthermore, to increase the tolerance and make the sidewall vertical and smooth, we coated different characteristics of photoresist sensitivity to the upper and lower layers. After the development, the mushroom-type photoresist makes Ni easier to strip while in the lift-off process, thus increasing the quality of the whole metalens. Our experiment shows that the focal lengths and focusing efficiencies corresponding to the two polarizations are similar to the simulation results. The proposed electrically modulated bifocal metalens can be utilized in different applications and combined with other optical components.
本文描述了电双焦超构透镜的设计过程和工艺优化。在我们的设计中，通过向扭曲向列型液晶（TN-LC）盒施加合适的电压来控制水平和垂直偏振。每个纳米结构被设计为长方体，使不同偏振的光经历不同的相位延迟，从而产生双焦点。由于最小物理尺寸可达50 nm以及最大纵横比高达15，我们选择光刻方法来制造我们的超构透镜。此外，为了提高宽容度并使侧壁垂直且光滑，我们在上下层涂覆了具有不同特性的光刻胶感光度。显影后，蘑菇型光刻胶使镍在剥离过程中更易于剥离，从而提高了整个超构透镜的质量。我们的实验表明，对应于两种偏振的焦距和聚焦效率与模拟结果相似。所提出的电调制双焦超构透镜可用于不同应用，并可与其他光学元件结合使用。
