Abstract
A key goal of metalens research is to achieve wavefront shaping of light using optical elements with thicknesses on the order of the wavelength. Here we demonstrate ultrathin highly efficient crystalline titanium dioxide metalenses at blue, green, and red wavelengths (λ0 = 453 nm, 532 nm, and 633 nm, respectively) based on symmetric slab waveguide theory. These metalenses are less than 488 nm-thick and capable of focusing incident light into very symmetric diffraction-limited spots with strehl ratio and efficiency as high as 0.96 and 83%, respectively. Further quantitative characterizations about metalenses’ peak focusing intensities and focal spot sizes show good agreement with theoretical calculation. Besides, the metalenses suffer only about 10% chromatic deviation from the ideal spots in visible spectrum. In contrast with Pancharatnam–Berry phase mechanism, which limit their incident light at circular polarization, the proposed method enables metalenses polarization-insensitive to incident light.
Highlights
Conventional objectives generally consist of precision-engineered compound lenses which make them bulky and costly, limiting their applications and hindering their integration into compact and cost-effective systems
Many previous metalenses with this type were just designed by the 1D metasurfaces with several antennas [30,31,32,33,34] in a period or 2D metasurfaces with dozens of antennas in whole [20,35,36], these simple and insufficient arrays cannot produce as good wavefronts as possible to ensure the high performance of metalenses that are comparable or even superior to conventional lenses
We can note that the designed metalens can work out very symmetric phase distribution as expected, which directly ensures the high symmetry of the focusing spots for designed metalenses
Summary
Conventional objectives generally consist of precision-engineered compound lenses which make them bulky and costly, limiting their applications and hindering their integration into compact and cost-effective systems. Many previous metalenses with this type were just designed by the 1D metasurfaces with several antennas [30,31,32,33,34] in a period or 2D metasurfaces with dozens of antennas in whole [20,35,36], these simple and insufficient arrays cannot produce as good wavefronts as possible to ensure the high performance of metalenses that are comparable or even superior to conventional lenses (see Figure S1) In this case, their focusing effects were hard to quantitatively analyze and usually were qualitatively demonstrated
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