Images perceived by human eyes or recorded by cameras are usually optical patterns with spatially varying intensity or color profiles. In addition to the intensity and color
the information of an image can be encoded in a spatially varying distribution of phase or polarization state. Interestingly
such images might not be able to be directly viewed by human eyes or cameras because they may exhibit highly uniform intensity profiles. Here
we propose and experimentally demonstrate an approach to hide a high-resolution grayscale image in a square laser beam with a size of less than half a millimeter. An image with a pixel size of 300 × 300 nm is encoded into the spatially variant polarization states of the laser beam
which can be revealed after passing through a linear polarizer. This unique technology for hiding grayscale images and polarization manipulation provides new opportunities for various applications
Chanana A, Paulsen A, Guruswamy S, Nahata A. Hiding multi-level multi-color images in terahertz metasurfaces.Optica2016;3: 1466–1470..
Yu NF, Genevet P, Kats MA, Aieta F, Tetienne JPet al. Light propagation with phase discontinuities: generalized laws of reflection and refraction.Science2011;334: 333–337..
Kildishev AV, Boltasseva A, Shalaev VM. Planar photonics with metasurfaces.Science2013;339: 1232009..
Estakhri NM, Alù A. Recent progress in gradient metasurfaces.J Opt Soc Am B2016;33: A21–A30..
Yu NF, Capasso F. Flat optics with designer metasurfaces.Nat Mater2014;13: 139–150..
Genevet P, Capasso F, Aieta F, Khorasaninejad M, Devlin R. Recent advances in planar optics: from plasmonic to dielectric metasurfaces.Optica2017;4: 139–152..
Huang LL, Chen XZ, Mühlenbernd H, Li GX, Bai BFet al. Dispersionless phase discontinuities for controlling light propagation.Nano Lett2012;12: 5750–5755..
Ma HF, Shen XP, Cheng Q, Jiang WX, Cui TJ. Broadband and high-efficiency conversion from guided waves to spoof surface plasmon polaritons.Laser Photonics Rev2014;8: 146–151..
Yu NF, Aieta F, Genevet P, Kats MA, Gaburro Zet al. A broadband, background-free quarter-wave plate based on plasmonic metasurfaces.Nano Lett2012;12: 6328–6333..
Jiang SC, Xiong X, Hu YS, Hu YH, Ma GBet al. Controlling the polarization state of light with a dispersion-free metastructure.Phys Rev X2014;4: 021026..
Lin DM, Fan PY, Hasman E, Brongersma ML. Dielectric gradient metasurface optical elements.Science2014;345: 298–302..
Arbabi A, Horie Y, Bagheri M, Faraon A. Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission.Nat Nanotechnol2015;10: 937–943..
Chen XZ, Huang LL, Mühlenbernd H, Li GX, Bai BBet al. Dual-polarity plasmonic metalens for visible light.Nat Commun2012;3: 1198..
Chen WT, Yang KY, Wang CM, Huang YW, Sun Get al. High-efficiency broadband meta-hologram with polarization-controlled dual images.Nano Lett2014;14: 225–230..
Khorasaninejad M, Chen WT, Devlin RC, Oh J, Zhu AYet al. Metalenses at visible wavelengths: diffraction-limited focusing and subwavelength resolution imaging.Science2016;352: 1190–1194..
Guo R, Rusak E, Staude I, Dominguez J, Decker Met al. Multipolar coupling in hybrid metal-dielectric metasurfaces.ACS Photonics2016;3: 349–353..
Yin XB, Ye ZL, Rho J, Wang Y, Zhang X. Photonic spin Hall effect at metasurfaces.Science2013;339: 1405–1407..
Lin J, Mueller JB, Wang Q, Yuan GH, Antoniou Net al. Polarization-controlled tunable directional coupling of surface plasmon polaritons.Science2013;340: 331–334..
Ye WM, Zeuner F, Li X, Reineke B, He Set al. Spin and wavelength multiplexed nonlinear metasurface holography.Nat Commun2016;7: 11930..
Grady NK, Heyes JE, Chowdhury DR, Zeng Y, Reiten MTet al. Terahertz metamaterials for linear polarization conversion and anomalous refraction.Science2013;340: 1304–1307..
Ni XJ, Wong ZJ, Mrejen M, Wang Y, Zhang X. An ultrathin invisibility skin cloak for visible light.Science2015;349: 1310–1314..
Genevet P, Yu NF, Aieta F, Lin J, Kats MAet al. Ultra-thin plasmonic optical vortex plate based on phase discontinuities.Appl Phys Lett2012;100: 013101..