Abstract
Optical metasurfaces enable novel ways to locally manipulate light's amplitude, phase, and polarization, underpinning a newly viable technology for applications, such as high‐density optical storage, holography, and displays. Here, a high‐security‐level platform enabled by centimeter‐scale plasmonic metasurfaces with full‐color, high‐purity, and enhanced‐information‐capacity properties is proposed. Multiple types of independent information can be embedded into a single metamark using full parameters of light, including amplitude, phase, and polarization. Under incoherent white light, the metamark appears as a polarization‐ and angle‐encoded full‐color image with flexibly controlled hue, saturation, and brightness, while switching to multiwavelength holograms under coherent laser illumination. More importantly, for actual applications, the extremely shallow functional layer makes such centimeter‐scale plasmonic metamarks suitable for cost‐effective mass production processes. Considering these superior performances of the presented multifunctional plasmonic metasurfaces, this work may find wide applications in anticounterfeiting, information security, high‐density optical storage, and so forth.
Highlights
Optical metasurfaces enable novel ways to locally manipulate light’s ampli- 1
As their 2D counterparts, metasurfaces consisting of subwavelength structures enable flexible manipulight, the metamark appears as a polarization- and angle-encoded fulllation of light’s fundamental properties color image with flexibly controlled hue, saturation, and brightness, while switching to multiwavelength holograms under coherent laser illumination
To prevent being faked by traditional cheap counterparts, a decryption device consisting of two linear polarizers, one beam splitter, and one quarter waveplate is employed to carry out the second level of security checking using the polarization degree of freedom, and the information hidden in the crosspolarized component can be decoded
Summary
The fact that the high-purity color is carried on the crosspolarized component can add an extra degree of freedom for information encryption, but it requires the decryption device to generate broadband CP light and filter the copolarized component. Assuming that a 1D or 2D meta-atom array has the period of p along the x-direction and is obliquely illuminated at an angle of θi along the x-direction, the central wavelength of the 1st-order diffraction component at an observation angle of θo along the x-direction can be expressed as λ = p × (sinθi − sinθ0 ) (2). Where p indicates the period of the meta-atom; θi/θo represents the angle between the normal line and incident/observation direction. The observation angle refers to be close to 0°, so that the incident angle should be close to 90°
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