High numerical aperture microwave metalens

Abstract

The numerical aperture (NA) of a lens determines its focusing resolution capability and the maximum light collection or emission angle. In this Letter, an ultrathin high NA metalens operating in the microwave band is designed and demonstrated both numerically and experimentally. The proposed element is constructed by a multi-layer complementary split ring resonator, which can cover full 2 π phase shift simultaneously with high transmission magnitude by varying its radius gradually. The numerical and experimental results reveal that the designed ultrathin (thickness is only ∼ 0.23 λ ) metalens can focus normal incident microwave efficiently to a spot of full width at half-maximum (FWHM) as small as ∼ 0.54 λ with a corresponding high NA exceeding 0.9. Besides, the high NA metalens also possesses a relatively large focusing efficiency with a peak 48% within considered broad frequency range from 7.5 to 10 GHz. The performances of the presented metalens can be comparable or even superior to nowadays high-quality optical metalenses and represent an important step to develop a high-performance metalens in low spectrum. Besides, it can greatly facilitate the development of some novel miniaturized devices like a high-gain low profile scanning antenna, an ultra-compact retroreflector, and cloaks.

Liquid crystal embedded dielectric metalens for active focal length tuning at the microwave range

“…Metasurfaces [4][5][6] , artificial electromagnetic microstructures with freely designed functionalities, are recently introduced to fabricate the microwave lenses, i.e., metalenses. By carefully tailoring the resonant property of the meta-unit to control the amplitude, phase and frequency of the electromagnetic wave, high numerical aperture (NA) metalens, ultrathin flat metalens, broadband achromatic metalens and far-field subwavelength imaging have been achieved [7][8][9][10] . To realize large phase shift and high transmission, many of them are composed of multilayer metallic resonator arrays 7,[11][12][13] , which add to the design and fabrication complexity.…”

“…By carefully tailoring the resonant property of the meta-unit to control the amplitude, phase and frequency of the electromagnetic wave, high numerical aperture (NA) metalens, ultrathin flat metalens, broadband achromatic metalens and far-field subwavelength imaging have been achieved [7][8][9][10] . To realize large phase shift and high transmission, many of them are composed of multilayer metallic resonator arrays 7,[11][12][13] , which add to the design and fabrication complexity. Dielectric metalenses are easier to design and fabricate compared with their metallic counterparts 14,15 .…”

Beam shaping for magnetoelectric transverse electromagnetic horn by using gradient refractive index lens

“…9 These metamaterial unit cells are easily fabricated with insulated substrate and etched metal. 10 This novel design method can overcome the disadvantages of traditional lenses, such as bulk, heavyweight, and difficulty of realization. 11,12 However, the miniaturization of metalens relies on the high effective permittivity of the unit cells.…”

“…Some kinds of metamaterial unit cells have been proposed to design gradient‐refractive‐index (GRIN) lenses, such as the flat lens, 7 Luneburg lens, 8 and fisheye lens 9 . These metamaterial unit cells are easily fabricated with insulated substrate and etched metal 10 . This novel design method can overcome the disadvantages of traditional lenses, such as bulk, heavyweight, and difficulty of realization 11,12 .…”

Broadband, large-numerical-aperture and high-efficiency microwave metalens by using a double-layer transmissive metasurface

“…ecently, metalens has become a frontier and hot topic in the field of metasurfaces and/or metamaterials. [1][2][3][4][5][6][7][8][9][10][11] Based on the efficient light manipulation on the ultrathin and flat interface with a series of phase gradient elements, metalenses provide an innovative platform for bending, collimating and focusing an incident wave. The focusing performances of metalens are definitely the core and can also determine its scope for further practical applications.…”