Ultrahigh Numerical Aperture Metalens at Visible Wavelengths
Ultrahigh Numerical Aperture Metalens at Visible Wavelengths
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可见波长处的超高数值孔径超透镜
DOI：
10.1021/acs.nanolett.8b01570
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发表时间：
2018-07-01
期刊：
影响因子：
10.8
通讯作者：
Li, Juntao
中科院分区：
文献类型：
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作者：
Liang, Haowen;Lin, Qiaoling;Li, Juntao
亚波长成像需要使用高数值孔径（NA）透镜以及浸没液体，以便实现最高可能的分辨率。继最近在超颖表面方面取得令人兴奋的进展，实现了高效聚焦和新颖的光束整形之后，展示超高NA超透镜的竞赛正在进行。到目前为止，已经证明的最高NA是NA = 1.1，使用TiO 2超透镜和背浸实现。在这里，我们介绍并展示了超透镜与高NA和高透射率在可见光范围内，基于晶体硅（c-Si）。与TiO 2相比，硅的折射率更高，这使我们能够进一步推动NA。该设计使用几何相位方法，也称为Pancharatnam Berry（P-B）相位，我们使用混合优化算法（HOA）确定纳米块的排列。我们展示了NA = 0.98的超透镜在空气中，带宽（半高全宽，fwhm）为274 nm，在532 nm波长的聚焦效率为67%，这是接近的二氧化钛超透镜的传输性能。此外，独特的是，我们的超透镜可以前浸没到浸没油中，并在实验上达到1.48的NA，在理论上达到1.73，从而证明了我们所知的可见光范围内任何超透镜的最高NA。制造过程与微电子技术完全兼容，因此可扩展。我们设想前浸没设计有利于实现超高NA超透镜以及浸没超透镜双合透镜，从而将超表面推向实际应用，如高分辨率，低成本共聚焦显微镜和消色差透镜。
Subwavelength imaging requires the use of high numerical aperture (NA) lenses together with immersion liquids in order to achieve the highest possible resolution. Following exciting recent developments in metasurfaces that have achieved efficient focusing and novel beam-shaping, the race is on to demonstrate ultrahigh-NA metalenses. The highest NA that has been demonstrated so far is NA = 1.1, achieved with a TiO2 metalens and back-immersion. Here, we introduce and demonstrate a metalens with a high NA and high transmission in the visible range, based on crystalline silicon (c-Si). The higher refractive index of silicon compared to TiO2 allows us to push the NA further. The design uses the geometric phase approach also known as the Pancharatnam Berry (P-B) phase, and we determine the arrangement of nanobricks using a hybrid optimization algorithm (HOA). We demonstrate a metalens with NA = 0.98 in air, a bandwidth (full width at half-maximum, fwhm) of 274 nm, and a focusing efficiency of 67% at 532 nm wavelength, which is close to the transmission performance of a TiO2 metalens. Moreover, and uniquely so, our metalens can be front-immersed into immersion oil and achieve an ultrahigh NA of 1.48 experimentally and 1.73 theoretically, thereby demonstrating the highest NA of any metalens in the visible regime reported to the best of our knowledge. The fabricating process is fully compatible with microelectronic technology and therefore scalable. We envision the front-immersion design to be beneficial for achieving ultrahigh-NA metalenses as well as immersion metalens doublets, thereby pushing metasurfaces into practical applications such as high resolution, low-cost confocal microscopy and achromatic lenses.