Research ArticlePHYSICS

Addressable metasurfaces for dynamic holography and optical information encryption

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Science Advances  15 Jun 2018:
Vol. 4, no. 6, eaar6768
DOI: 10.1126/sciadv.aar6768
  • Fig. 1 Working principle of the dynamic metasurface pixels.

    (A) Schematic of hydrogen-responsive Mg nanorods (200 nm × 80 nm × 50 nm), which are sandwiched between a Ti (5 nm)/Pd (10 nm) capping layer and a Ti (3 nm) adhesion layer. (B) Measured scattering spectra of such a nanorod in Mg (on) and MgH2 (off) states. Before hydrogenation, the Mg nanorod exhibits a strong plasmonic resonance (red curve), whereas after hydrogenation (10% H2) the MgH2 rod shows a nearly featureless spectrum (blue curve). The process is reversible through dehydrogenation using O2 (20%). a.u., arbitrary units. (C) Simulated phase delay for the different phase levels. The orientation of the nanorod at each phase level is shown.

  • Fig. 2 Metasurface hologram with dynamic and static patterns.

    (A) Two holographic patterns, harmony and peace, reconstructed from two independent phase profiles containing Mg/Pd (P1) and Au (P2) nanorods as dynamic and static pixels, respectively. Ti is omitted for conciseness. The two sets of pixels are merged together with a displacement vector of (300 nm, 300 nm). (B) Overview SEM image of the hybrid plasmonic metasurface. The Au (P2) nanorods are represented in yellow color. Inset: Enlarged SEM image of the unit cell (600 nm × 600 nm). (C) Time evolutions of P1 (solid line) and P2 (dashed line) during hydrogenation and dehydrogenation. The scattered intensities at resonance peak positions of P1 and P2 are used to track the dynamic processes, respectively. P1 can be switched off/on through hydrogenation/dehydrogenation, whereas P2 stays at the on state. (D) Schematic of the optical setup for capturing the holographic images. QWP, quarter-wave plate; LP, linear polarizer. (E) Representative snapshots of the holographic images during hydrogenation and dehydrogenation. Harmony (left) can be switched off/on using H2/O2, whereas peace (right) stays still.

  • Fig. 3 Metasurface hologram with differently sequenced dynamics.

    (A) Mg/Pd (P1) and Mg/Pd/Cr (P3) nanorods work as dynamic pixels with different reaction kinetics. Overview SEM image of the hybrid plasmonic metasurface as well as the enlarged SEM image of the unit cell (600 nm × 600 nm). The Mg/Pd/Cr (P3) nanorods are represented in blue color. (B) Time evolutions of P1 (solid line) and P3 (dash-dotted line) during hydrogenation and dehydrogenation. The scattered intensities at resonance peak positions of P1 and P3 are used to track the dynamic processes, respectively. (C) Representative snapshots of the holographic images during hydrogenation and dehydrogenation. H2(1) or H2(2) refers to a hydrogenation process until the first or second feature completes transition. Both the portrait of Marie Curie and the chemical elements Po and Ra can be switched on and off independently.

  • Fig. 4 Metasurface-based dynamic geometric codes.

    (A) Chart of the geometric codes for 0 to 9. (B) Reconstructed holographic image of 1. Each Arabic number in the chart can be expressed by a specific holographic image reconstructed from the same metasurface multiplexed by three sets of pixels: P1 (Mg/Pd), P2 (Au), and P3 (Mg/Pd/Cr). To achieve holograms with uniform intensity distributions, P2 is used twice in each unit cell. (C) Helicity of light, H2, O2, and reaction duration constitute multiple keys to generate the numbers 0 to 9, which are transformable with the same metasurface. The centrosymmetry point is indicated by a white circle in each plot, highlighting the location of the zero-order reflected light. A coding rule is defined that each number corresponds to a union set of the two holographic patterns in zones I and II.

  • Fig. 5 Proof-of-concept experiment for optical information encryption and decryption.

    Alice encrypts her messages for Tim (88), Bob (73), Ted (99), and so forth, all on one metasurface. Identical samples are sent to multiple receivers, who decrypt their respective messages according to the customized keys. The keys contain customer-specific information on the helicity of light (LCP, RCP, or LP), hydrogenation (H2), dehydrogenation (O2), and reaction duration. Different messages can be read out, corresponding to love and kisses for Tim, best regards for Bob, go away for Ted, and so forth, in Morse codes.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaar6768/DC1

    fig. S1. Dynamic scattering spectra of a Mg nanorod during hydrogenation and dehydrogenation.

    fig. S2. Time evolution of P1 during hydrogenation and dehydrogenation in multicycles.

    fig. S3. High quality and high resolution of the holographic patterns.

    fig. S4. Principle of the multiplexed metasurfaces.

    fig. S5. Reconstructed holographic patterns in different zones upon LCP, RCP, or LP light illumination.

    movie S1. Evolution of the metasurface hologram with static and dynamic patterns.

    movie S2. Evolution of the metasurface hologram with sequenced dynamics.

    movie S3. Dynamic transformation among different numbers.

    References (3135)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Dynamic scattering spectra of a Mg nanorod during hydrogenation and dehydrogenation.
    • fig. S2. Time evolution of P1 during hydrogenation and dehydrogenation in multicycles.
    • fig. S3. High quality and high resolution of the holographic patterns.
    • fig. S4. Principle of the multiplexed metasurfaces.
    • fig. S5. Reconstructed holographic patterns in different zones upon LCP, RCP, or LP light illumination.
    • References (31–35)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). Evolution of the metasurface hologram with static and dynamic patterns.
    • movie S2 (.avi format). Evolution of the metasurface hologram with sequenced dynamics.
    • movie S3 (.avi format). Dynamic transformation among different numbers.

    Download Movies S1 to S3

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