Off-axis spectral confocal metasurfaces with linear dispersion in a broad bandwidth

Optics Communications(2023)

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Abstract
Optical metasurfaces offer significant possibilities for miniaturization and expanding the capabilities of conventional optical elements due to their superb wavefront regulation abilities. In this paper, we propose a design approach that precisely controls the chromatic dispersion of anisotropy silicon nanobricks to create off-axis spectral confocal metasurfaces with linear dispersion in short-wave infrared range (1600 nm–2400 nm). Firstly, a single-layer off-axis spectral confocal metasurfaces with an aperture diameter of 60μm and a fixed x-direction focal length component of 50μm is presented to demonstrate the effectiveness of approach. At the maximum and minimum frequencies, the total focal lengths are 125μm and 83.33μm, respectively. Subsequently, we analyze the possible limitations of designing single-layer metasurfaces and overcome them by adopting doublet metasurfaces. An example of double-layer off-axis spectral confocal metasurfaces with a radius of 50μm and an off-axis distance of 80μm is showcased to introduce the approach, and the focal lengths range between the maximum and minimum frequencies is 66.67μm, larger than that of single-layer metasurfaces. The numerical simulation results validate the practicality of our design approach, which can be generalized for other customized functionalities metasurfaces with a broad bandwidth.
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Key words
Metasurfaces, Spectral confocal, Dispersion
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