宽带矢量超平面光学器件，通过通用逼近器在可见光区的实验效率高达99%
Broadband vectorial ultra-flat optics with experimental efficiency up to 99% in the visible via universal approximators
摘要：
将传统光学器件集成到紧凑的纳米结构表面是平面光学器件的目标。尽管该技术取得了巨大的进步，但由于可见光中的有限效率（平均低于$60\%$），现实世界的应用仍然存在关键的挑战，这源于波长厚（$\approx 500$ nm）结构中的吸收损耗。另一个问题是实现按需光学部件，用于在反射和透射中同时控制可见频率下的矢量光，并且具有预定的波前形状。在这项工作中，我们开发了一种逆向设计方法，允许实现高效（高达$99\%$）超平坦（厚度低至$50$ nm）光学器件，用于矢量光控制和宽带输入输出响应所需的波前形状。该方法利用了通用逼近器的隐藏网络，该网络存在于适当设计的半导体纳米结构的物理层中。这些表面的超平坦特性使其性能接近统一，从而将吸收损耗降低到几乎可以忽略的值。在实验中，我们讨论偏振分束器，比较其性能与从直接和反向设计技术获得的最佳结果，以及由分色镜和平面光学显示器的基本单元表示的新的平面光学组件，该平面光学显示器仅使用两个子像素创建全色，克服了传统LCD/OLED技术的限制，每个复合颜色需要三个子像素。我们的器件采用互补金属氧化物半导体（CMOS）兼容工艺制造，使其能够以低廉的成本进行大规模生产。
英文摘要：
Integrating conventional optics into compact nanostructured surfaces is the goal of flat optics. Despite the enormous progress of this technology, there are still critical challenges for real world applications due to a limited efficiency in the visible, on average lower than $60\%$, which originates by absorption losses in wavelength thick ($\approx 500$nm) structures. Another issue is the realization of on-demand optical components for controlling vectorial light at visible frequencies simultaneously in both reflection and transmission, and with a predetermined wavefront shape. In this work, we developed an inverse design approach that allows the realization of highly efficient (up to $99\%$) ultra-flat (down to $50$nm thick) optics for vectorial light control and broadband input-output responses on a desired wavefront shape. The approach leverages on a hidden network of universal approximators, which exist in the physical layer of suitably engineered semiconductor nanostructures. Near unity performance results from the ultra-flat nature of these surfaces, which reduces absorption losses to almost negligible values. Experimentally, we discuss polarizing beam splitters, comparing their performances with the best results obtained from both direct and inverse design techniques, and new flat-optics components represented by dichroic mirrors and the basic unit of a flat optics display that creates full colors by using only two sub-pixels, overcoming the limitations of conventional LCD/OLED technologies that require three sub-pixels for each composite color. Our devices are manufactured with a complementary metal-oxide-semiconductor (CMOS) compatible process, making them scalable for mass production at inexpensive costs.
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