T. J. Watson Laboratory of Applied Physics, California Institute of Technology, 1200 E California Blvd., Pasadena, California 91125, USA.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
Nat Commun. 2015 May 7;6:7069. doi: 10.1038/ncomms8069.
Flat optical devices thinner than a wavelength promise to replace conventional free-space components for wavefront and polarization control. Transmissive flat lenses are particularly interesting for applications in imaging and on-chip optoelectronic integration. Several designs based on plasmonic metasurfaces, high-contrast transmitarrays and gratings have been recently implemented but have not provided a performance comparable to conventional curved lenses. Here we report polarization-insensitive, micron-thick, high-contrast transmitarray micro-lenses with focal spots as small as 0.57 λ. The measured focusing efficiency is up to 82%. A rigorous method for ultrathin lens design, and the trade-off between high efficiency and small spot size (or large numerical aperture) are discussed. The micro-lenses, composed of silicon nano-posts on glass, are fabricated in one lithographic step that could be performed with high-throughput photo or nanoimprint lithography, thus enabling widespread adoption.
薄于波长的平面光学器件有望替代传统的自由空间波前和偏振控制元件。对于成像和片上光电集成应用，透光平面透镜尤其有趣。最近已经实现了几种基于等离子体超表面、高对比度透射阵列和光栅的设计，但它们的性能无法与传统的曲面透镜相媲美。在这里，我们报告了具有偏振不敏感、微米厚度、高对比度的透射阵列微透镜，其焦斑小至 0.57λ。测量的聚焦效率高达 82%。讨论了超薄透镜设计的严格方法，以及高效率和小光斑尺寸（或大数值孔径）之间的权衡。这些微透镜由玻璃上的硅纳米柱组成，可通过一次光刻步骤制造，该步骤可以采用高通量的光或纳米压印光刻来完成，从而实现广泛应用。
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