Dielectric metasurfaces have significant potential for delivering miniaturized optical systems with versatile functionalities, leading to applications in various fields such as orbital angular momentum generation, imaging, and holography. Among the different materials, crystalline silicon has the advantage of technological maturity and high refractive index, which increases design flexibility and processing latitude. The second, and often overlooked, advantage of silicon is that it affords embedding the metasurface in a protective material such as silica, which is essential for practical applications. The trade-off against this high refractive index is silicon's absorption at visible wavelength, which requires new design strategies. Here, such a strategy based on metasurfaces supporting air modes is identified that can lead to a transmission efficiency as high as 87% at a wavelength of 532 nm. This exceptional efficiency is obtained by using the high index to confine the electric field in the periphery of the meta-atoms, thereby reducing absorption losses. As an example, the design of a fully embedded metasurface is described that can generate vortex beams with various orders of orbital angular momentum. It is envisioned that the proposed strategy paves the way for practical applications of high-efficiency metasurfaces based on crystalline silicon.
Bibliographical noteFunding Information:
This work was supported by the Guangdong Provincial Key R&D Program (No. 2019B010152001), National Natural Science Foundation of China (Nos. 11974436, 12074444, and 11704421), Guangdong Basic and Applied Basic Research Foundation (Nos. 2020B1515020019 and 2020A1515011184). H.L. acknowledges support by Innovation Group Project of Southern Marine Science and Engineering Guangdong. E.R.M. acknowledges support by Grant No. 2020/00619‐4, São Paulo Research Foundation (FAPESP). T.F.K. acknowledges support by UK Research & Innovation under Contract Nos. EP/P030017/1 and EP/T020008/1.
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- crystalline silicon
- optical metasurfaces
- visible wavelength