Fourier transform, mapping the information in one domain to its reciprocal space, is of fundamental significance in real-time and parallel processing of massive data for sound and image manipulation. As a powerful platform of high-efficiency wave control, Huygens’ metasurface may offer to bridge the electromagnetic signal processing and analog Fourier transform at the hardware level and with remarkably improved performance. We here demonstrate a Huygens’ metasurface hologram, where the image pattern can be self-rotated or projected in free space by modulating the phase distribution based on the rotational invariance, time-shifting and scaling properties of Fourier transform. Our proof-of-concept experiment shows high-efficiency imaging operation in accordance with theoretical predictions, validating the proposed scheme as an ideal way to perform largely parallel spatial-domain mathematical operations in the analog domain using electromagnetic fields.
achieving high holographic image quality. By elaborately arranging the geometries of nanoantennas [3] or orientation angles [4,5] of metaatoms, desired abrupt interfacial phase shift at designated points within subwavelength thickness can be realized. Therefore, metasurface has been applied to versatile applications, including directional radiators, [6] thin-film cloaking, [7,8] planar lenses, [9] optical vortex beam generators, [10,11] and digital holograms. [12][13][14][15][16] Compared to the hologram based on traditional optical devices, metasurface hologram improves imaging efficiency, [17] spatial resolution, [18] and robustness against fabrication tolerances. [19] Hence, metasurface holograms have been widely applied in the terahertz, infrared, and visible frequency bands. Nevertheless, the transmittance efficiency of transmission-phaseonly metasurface hologram is still limited by cross-polarization transformation losses.Huygens metasurface can significantly improve the transmittance efficiency and achieve full phase-shift coverage, since it enables to fully control the phase and amplitude of copolarized transmitted wave without polarization conversion losses by integrating designed electric and magnetic dipoles into each metaatom. [20] On account of its superior wave-manipulating ability, various correlative researches have been reported in beam-refracting, [21] focusing, [22,23] beam-shaping, [24] and holographic imaging. [25] Here, we experimentally realize microwave holographic imaging recorded by Huygens metasurfaces with the modulation of focal intensity distribution. By judiciously designing geometrical parameters of electric and magnetic dipoles, 15 metaatoms which cover a 2π phase range with close-to-unity transmission amplitude are extracted for holographic imaging. Moreover, a new holographic algorithm is presented to divert the incident energy to specified focal positions and adjust the energy allocation among focal points. Three parameters are adopted in this work to evaluate the main aspects of image quality, including transmittance efficiency, imaging efficiency, and root-mean-square error (RMSE) of focal intensity ratio. The numerical simulations and experimental results of holographic images carried out in the microwave regime agree well with theoretical predictions, which verify the feasibility and outstanding image quality of the proposed Huygens metasurface holograms, paving the way toward highly efficient microwave holographic imaging.Huygens metasurface, an implementation of Huygens principle with metasurface, shows great potential in the manipulation of electromagnetic wave by elaborately designed subwavelength scale metaatoms with full phase coverage and high transmission amplitude. Here, a multiphase hologram with Huygens metasurface is demonstrated in microwave regime, and a novel algorithm method is proposed to modulate energy distribution among focal points. The proof-of-concept experiments show superior microwave holographic images with 89% transmittance efficiency, 59% imaging...
Computational meta-optics brings a twist on the accelerating hardware with the benefits of ultrafast speed, ultra-low power consumption, and parallel information processing in versatile applications. Recent advent of metasurfaces have enabled the full manipulation of electromagnetic waves within subwavelength scales, promising the multifunctional, high-throughput, compact and flat optical processors. In this trend, metasurfaces with nonlocality or multi-layer structures are proposed to perform analog optical computations based on Green’s function or Fourier transform, intrinsically constrained by limited operations or large footprints/volume. Here, we showcase a Fourier-based metaprocessor to impart customized highly flexible transfer functions for analog computing upon our single-layer Huygens’ metasurface. Basic mathematical operations, including differentiation and cross-correlation, are performed by directly modulating complex wavefronts in spatial Fourier domain, facilitating edge detection and pattern recognition of various image processing. Our work substantiates an ultracompact and powerful kernel processor, which could find important applications for optical analog computing and image processing.
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