Research ArticleAPPLIED SCIENCES AND ENGINEERING

Adaptive metalenses with simultaneous electrical control of focal length, astigmatism, and shift

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Science Advances  23 Feb 2018:
Vol. 4, no. 2, eaap9957
DOI: 10.1126/sciadv.aap9957
  • Fig. 1 Principle of strain field–mediated tunable metalens.

    A metasurface (left column) is constructed by digitizing an analog optical phase profile on a flat surface into discrete cells, each of which contains a metasurface element that locally imparts the required phase shift to the incident light to reconstruct the desired wavefront (middle column; dashed line: optical axis). The wavefront generated by the metasurface determines the subsequent beam shaping (right column). (A) Original: metasurface without stretch. (B) Defocus: metasurface with uniform and isotropic stretch. (C) Astigmatism: metasurface under asymmetric stretch. (D) Shift: metasurface displaced laterally in the x,y plane.

  • Fig. 2 DEA metalens device design.

    (A) A schematic of the device in which a metalens and a DEA with five addressable electrodes are combined to allow for electrical control over the strain field of the metasurface. (B) Optical microscope images (scale bars, 20 μm) at (i) no voltage, (ii) 2.5 kV applied to the center electrode (V5), and (iii) 2.75 kV applied to tune x astigmatism (concurrently, V1 and V3). The dark spots are defects (either missing or tilted silicon posts) introduced during the transfer process. The corresponding two-dimensional Fourier transforms (FTs) of (i) to (iii) are shown in (iv) to (vi), respectively (normalized amplitudes).

  • Fig. 3 Measurement of tuning.

    (A) (Left) Z-scan of the intensity profile showing two distinct focal lengths. (Center) Image of focal spot intensity profile (that is, x-y cross sections at the position of maximum intensity). (Right) Line scans of focal spot intensity image in the x (blue) and y (red) directions in comparison to the theoretical diffraction-limited spot size (black). a.u., arbitrary units. (B) Additional images of the focal spots at 1.5, 2, and 2.5 kV are shown, captured directly by the camera without the microscope objective (scale bars, 200 μm). (Bottom right) Measured focusing efficiency for varying voltages (see fig. S6C for setup). (C) Measurement of focal length tuning using the center electrode V5 for DL and SL (inset) devices. Blue circles represent optical measurement of device focal length as a function of applied voltage. The solid blue line indicates the fit of focal length data to Eq. 3 (R2 = 0.9915). Red triangles represent measurement of stretch as a function of the applied voltage. (D) Measured Zernike coefficients of the phase profile (calculated from microscope images of the lens center) showing targeted tuning of vertical astigmatism, whereas other Zernike coefficients exhibit little change. The large defocus value represents the designed focal power of the lens. (E) Measurement of x,y shift control showing two-axis displacement control from the focus position at 0 kV (yellow star) to various positions (red dots) as 1.9 kV is applied. The gray shaded area shows possible displacements, which can be accessed by concurrently activating combinations of electrodes.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaap9957/DC1

    fig. S1. Uniform stretch approximation.

    fig. S2. DEA platform.

    fig. S3. Metalens design elements.

    fig. S4. Optical measurements of a DEA, which consists of a prestretched (four times) acrylic elastomer (VHB Tape 4905, 3M) and SWCNT electrodes.

    fig. S5. Device design and operation.

    fig. S6. Measurement setup.

    fig. S7. Fitting measurement of focal length tuning using electrode V5.

    fig. S8. Measurement of x,y shift distortion.

    fig. S9. Response time measurement.

    table S1. Wavefront shaping with Zernike polynomials.

    movie S1. Reliability test.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Uniform stretch approximation.
    • fig. S2. DEA platform.
    • fig. S3. Metalens design elements.
    • fig. S4. Optical measurements of a DEA, which consists of a prestretched (four
      times) acrylic elastomer (VHB Tape 4905, 3M) and SWCNT electrodes.
    • fig. S5. Device design and operation.
    • fig. S6. Measurement setup.
    • fig. S7. Fitting measurement of focal length tuning using electrode V5.
    • fig. S8. Measurement of x,y shift distortion.
    • fig. S9. Response time measurement.
    • table S1. Wavefront shaping with Zernike polynomials.
    • Legend for movie S1

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Reliability test.

    Files in this Data Supplement:

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