Abstract
Metasurfaces have shown excellent ability in manipulating light fields. However, the intrinsic chromatic aberration impairs the quality of their broadband operation, which is a serious problem restricting the application of metadevices, especially metalenses. In this paper, a polarization-independent broadband achromatic metalens composed of engineered structures that have spatially varying gradient sizes is devised to focus the light over the mid-infrared region from 3 to 5 µm. The proposed dielectric metalens is constructed by an array of meta-units with a hollowed square pillar. By tuning its structural parameters, the optical response of the meta-unit turns out to be broadband achromatic, insensitive to the polarization state, and of high efficiency. Numerical simulation results show that the designed metalens can significantly suppress chromatic aberrations over a broad mid-infrared and hold a focusing efficiency of nearly 75%. Our work is beneficial to improving the mid-infrared broadband imaging quality and detection efficiency.
Highlights
Metasurfaces are composed of subwavelength electromagnetic resonators, providing arbitrarily spatial phase variation over the planar surfaces, which is demonstrated by the generalized Snell’s law.1 Due to the significant ability of metasurfaces in light field control, various compact devices have been designed, such as vortexbeam generators,2,3 polarization modulation and detection,4–6 light beam steering,7–9 and optical holography.10–12 In addition, toroidal metadevices based on toroidal metaphotonics and metaplasmonics have an advantage for managing intrinsic radiative losses.13 These devices possess the characteristic of lightweight, ultra-thin, and high design freedom compared to conventional elements
The normalized light field scitation.org/journal/adv intensity distribution in the x–z plane is shown in Fig. 5 with an 0.4 μm spacing of wavelength
Numerical simulations show that the achromatic metalens has excellent achromatic performance over the continuous broadband ranging from 3 to 5 μm
Summary
Metasurfaces are composed of subwavelength electromagnetic resonators, providing arbitrarily spatial phase variation over the planar surfaces, which is demonstrated by the generalized Snell’s law. Due to the significant ability of metasurfaces in light field control, various compact devices have been designed, such as vortexbeam generators, polarization modulation and detection, light beam steering, and optical holography. In addition, toroidal metadevices based on toroidal metaphotonics and metaplasmonics have an advantage for managing intrinsic radiative losses. These devices possess the characteristic of lightweight, ultra-thin, and high design freedom compared to conventional elements. Metasurfaces are composed of subwavelength electromagnetic resonators, providing arbitrarily spatial phase variation over the planar surfaces, which is demonstrated by the generalized Snell’s law.. Due to the significant ability of metasurfaces in light field control, various compact devices have been designed, such as vortexbeam generators, polarization modulation and detection, light beam steering, and optical holography.. Toroidal metadevices based on toroidal metaphotonics and metaplasmonics have an advantage for managing intrinsic radiative losses.. Toroidal metadevices based on toroidal metaphotonics and metaplasmonics have an advantage for managing intrinsic radiative losses.13 These devices possess the characteristic of lightweight, ultra-thin, and high design freedom compared to conventional elements. As an important application of metasurfaces, the metalens can be used as a lens to converge incident light beams and realize optical imaging while working in the planar mode.. As an important application of metasurfaces, the metalens can be used as a lens to converge incident light beams and realize optical imaging while working in the planar mode. The metalens is appreciated because it can be mass-produced by the nanofabrication process and is capable of being integrated into an optical system
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