Research ArticleAPPLIED OPTICS

Broadband and chiral binary dielectric meta-holograms

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Science Advances  13 May 2016:
Vol. 2, no. 5, e1501258
DOI: 10.1126/sciadv.1501258
  • Fig. 1 Effective aperture made of subwavelength structured dielectric.

    (A) Schematic diagram of two apertures separated by a center-to-center distance D on a glass substrate. The phase shift associated with light propagating from the two apertures along the direction θ is denoted as Δϕ. This phase difference is related to D and the wavelength, as shown in Eq. 1. (B) Schematic diagram of a cross section of two generic pixels (2Λ = 5.4 μm) of the hologram. Each pixel functions as an effective aperture consisting of six DRWs with subwavelength spacing (S = 380 nm), width (W = 120 nm), and height (H = 400 nm). (C) Far-field [Real(Ey)2] response of the effective aperture when the incident light is polarized along the y axis. This represents a two-dimensional finite-difference time domain simulation, where the DRWs are infinitely long along the y axis and the effective aperture extension along the x axis is 2Λ = 5.4 μm. Engineering the dispersive response of the DRWs results in highly directional diffraction, in which most of the transmitted light is funneled into the first orders whereas other diffraction orders are suppressed.

  • Fig. 2 Dispersion engineering and hologram design.

    (A) Diffraction angle of a pixel as a function of wavelength. Inset: Top view of the hologram pixel sized 5.4 μm × 5.4 μm (2Λ = 5.4 μm). The diffraction angle is calculated from the far-field response using finite-difference time domain simulations. The modeled diffraction angle closely follows the target angular dispersion θ = sin−1(λ/Λ) to cancel the wavelength dependence of the detour phase. (B) Schematic diagram showing the 256 × 256–pixel arrangement in the hologram. The required phase map is achieved through the displacement of each pixel. (C) Scanning electron microscopy (SEM) image of the device. Scale bar, 3 μm. Inset: A false-colored SEM image in which four pixels are highlighted with different colors. Scale bar, 1 μm. (D) Sketch of the experimental setup. The laser beam from a fiber-coupled supercontinuum laser is collimated by means of a fiber collimator. The polarization state of the laser beam is controlled by a linear polarizer (LP) followed by a half–wave plate (λ/2) before the laser beam illuminates the hologram (device). An image of the light distribution in the Fourier plane is obtained by means of a lens and an indium gallium arsenide (InGaAs) camera aligned along the direction of the first diffraction order. The lens is located at a focal length distance from both the device and the camera. For measurements in the visible range, the InGaAs camera is substituted by a color camera.

  • Fig. 3 Broadband phase distortion–free hologram.

    (A to D) Images generated when the hologram is illuminated with NIR light. (E) Absolute efficiency and extinction ratio (ER) as a function of wavelength. The drop in ER is due to the significant drop in the efficiency of the imaging camera at longer wavelengths. (F and G) Images corresponding to a hologram in which the IYL logo phase distribution is added to that of a Fresnel lens with a 2-cm total shift of the reconstruction plane. (F) Image captured under the same measurement conditions of (A) to (D). This image is blurry because the Fresnel lens phase profile encoded in the hologram moves the image plane 2 cm forward along the propagation direction. (G) The same image appears correctly in focus when the camera is moved 2 cm along the propagation direction. (H to K) Images generated by the hologram in the visible range. These images were captured by a color charge-coupled device camera.

  • Fig. 4 Chiral hologram.

    (A) A false-colored SEM image of four pixels of the hologram. Each pixel consists of two parts: in purple, those that impart the required phase map for letter “L” and in green, those for the phase map for letter “R.” Nanofins have a width (W) of 85 nm, a length (L) of 350 nm, a height (H) of 1000 nm, and a center-to-center distance of 500 nm. Scale bar, 1 μm. (B) Tilted view: SEM image of the hologram. Scale bar, 1 μm. (C to E) Images in the +1 diffraction order (false-colored) generated by the chiral hologram under different incident polarizations at λ = 1350 nm. Chiral hologram illuminated by (C) circularly right-polarized light, (D) circularly left-polarized light, and (E) linearly polarized light resulting in the appearance of the letters “R,” “L,” and “RL,” respectively.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/5/e1501258/DC1

    Meta-element

    Engineered dispersion of DRWs

    Quality of the designed intensity distribution in the reconstruction plane

    Optical image of the fabricated device

    Illumination with visible light

    Pixel far field in the visible range

    Polarization-dependent response of the meta-element

    Chiral hologram features

    fig. S1. Meta-element.

    fig. S2. Engineered dispersion of DRWs.

    fig. S3. Hologram performance at different wavelengths.

    fig. S4. Optical image of the holographic device.

    fig. S5. Image of the 2015 IYL logo.

    fig. S6. Far-field response of the meta-element in the visible range.

    fig. S7. Polarization-selective meta-element.

    fig. S8. Efficiency and ER of the chiral hologram.

    fig. S9. Broadband chiral hologram.

  • Supplementary Materials

    This PDF file includes:

    • Meta-element
    • Engineered dispersion of DRWs
    • Quality of the designed intensity distribution in the reconstruction plane
    • Optical image of the fabricated device
    • Illumination with visible light
    • Pixel far field in the visible range
    • Polarization-dependent response of the meta-element
    • Chiral hologram features
    • fig. S1. Meta-element.
    • fig. S2. Engineered dispersion of DRWs.
    • fig. S3. Hologram performance at different wavelengths.
    • fig. S4. Optical image of the holographic device.
    • fig. S5. Image of the 2015 IYL logo.
    • fig. S6. Far-field response of the meta-element in the visible range.
    • fig. S7. Polarization-selective meta-element.
    • fig. S8. Efficiency and ER of the chiral hologram.
    • fig. S9. Broadband chiral hologram.

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