Optically reconfigurable metasurfaces and photonic devices based on phase change materials

Journal name:
Nature Photonics
Volume:
10,
Pages:
60–65
Year published:
DOI:
doi:10.1038/nphoton.2015.247
Received
Accepted
Published online

Abstract

Photonic components with adjustable parameters, such as variable-focal-length lenses or spectral filters, which can change functionality upon optical stimulation, could offer numerous useful applications. Tuning of such components is conventionally achieved by either micro- or nanomechanical actuation of their constituent parts, by stretching or by heating. Here, we report a novel approach for making reconfigurable optical components that are created with light in a non-volatile and reversible fashion. Such components are written, erased and rewritten as two-dimensional binary or greyscale patterns into a nanoscale film of phase-change material by inducing a refractive-index-changing phase transition with tailored trains of femtosecond pulses. We combine germanium–antimony–tellurium-based films with a diffraction-limited resolution optical writing process to demonstrate a variety of devices: visible-range reconfigurable bichromatic and multi-focus Fresnel zone plates, a super-oscillatory lens with subwavelength focus, a greyscale hologram, and a dielectric metamaterial with on-demand reflection and transmission resonances.

At a glance

Figures

  1. Writing of reconfigurable photonic devices in a phase-change film (artistic impression).
    Figure 1: Writing of reconfigurable photonic devices in a phase-change film (artistic impression).

    Various optical components, including lenses, diffractive elements and resonant metamaterials, can be written with high accuracy in the chalcogenide glass phase-change film by trains of femtosecond pulses (‘write’ channel). Pulses from a Ti:sapphire laser are focused and repositioned across the surface of the film by a computer-controlled spatial light modulator and electro-optical pulse picker. Optical excitation changes the complex refractive index of the film by converting continuously from the amorphous to crystalline state, allowing films with complex refractive-index profiles to be written. The written pattern can also be erased by the same laser using different illumination conditions. The results are observed through the ‘read’ channel.

  2. Binary and greyscale devices optically written in the phase-change film.
    Figure 2: Binary and greyscale devices optically written in the phase-change film.

    a, Fresnel zone-plate pattern imaged at λ = 633 nm. b, Microscope image of the optical hotspot as focused by the Fresnel zone-plate at λ = 730 nm. c, Intensity cross-section of the hot spot. d, Binary super-oscillatory lens pattern imaged at λ = 633 nm. e, Microscope image of the optical hotspot as focused by the binary super-oscillatory lens at λ = 730 nm, 43.8 µm from the lens. f, Intensity cross-section of the super-oscillatory hotspot. g, Image of the fabricated eight-level greyscale hologram designed to generate a V-shaped five-spot pattern. Inset: computer-generated greyscale hologram with 121 × 121 pixels. Scale bar: 10 µm. h, Microscope image of the generated five-spot pattern in transmission mode, 100 µm away from the sample surface, λ = 730 nm. Scale bar: 5 µm. i, Continuous phase change of reflectance, ΔR= (RcRa)/Ra, of the partially crystallized chalcogenide glass film as a function of the number of femtosecond pulses that excite phase change in the film. Ra is the reflectance of the amorphous film and Rc is the reflectance of the partially crystallized mark. The single pulse energy is 0.39 nJ, corresponding to a fluence of ∼140 mJ cm–2.

  3. Writing planar wavelength multiplexing focusing devices.
    Figure 3: Writing planar wavelength multiplexing focusing devices.

    a, Lens focusing two different wavelengths to spatially separated foci on the focal plane (deliberate transverse chromatic aberration). b, Lens focusing two different optical wavelengths in the same focus (corrected chromatic aberration). c,d, Optical images of the lens patterns in a GST film with deliberate transverse chromatic aberration (c) and corrected chromatic aberration (d). Each pattern is composed of 121 × 121 pixels. e,f, Focal spots of lenses c and d at λ = 730 nm. g,h, Focal spots of the same lenses at λ = 900 nm. Note that pattern c focuses light of different wavelengths in different spots, while pattern d focuses light of both wavelengths in the same spot position. Scale bar: 10 µm.

  4. Dynamically optically reconfigurable zone-plate device.
    Figure 4: Dynamically optically reconfigurable zone-plate device.

    a, Two superimposed Fresnel zone patterns focusing a plane wave into two different foci. b,c, One of the Fresnel zone patterns is erased (b) and then restored again (c). d, Superimposed Fresnel zone patterns imaged at λ = 633 nm as they are first written. e, The second Fresnel zone pattern is erased. f, Both patterns are restored. gi, Transmission focal spots as generated by patterns df at λ = 730 nm. Scale bar: 10 µm.

  5. Writing a dielectric metamaterial.
    Figure 5: Writing a dielectric metamaterial.

    a, Reflection image of the dielectric metamaterial written into the GST phase-change film. The 1.78 µm × 1.19 µm unit cell of the pattern consists of two phase-change marks. b,c, Reflection (red line) and transmission (green line) spectra of the metamaterial for light polarized along the horizontal direction (b) and the vertical direction (c), as indicated in a.

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Author information

Affiliations

  1. Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Highfield, Southampton SO17 1BJ, UK

    • Qian Wang,
    • Edward T. F. Rogers,
    • Behrad Gholipour,
    • Chih-Ming Wang &
    • Nikolay I. Zheludev
  2. Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore

    • Qian Wang &
    • Jinghua Teng
  3. Institute for Life Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK

    • Edward T. F. Rogers
  4. Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371, Singapore

    • Behrad Gholipour,
    • Guanghui Yuan &
    • Nikolay I. Zheludev

Contributions

N.I.Z. conceived the idea of optical reconfigurable photonics devices. Q.W. built the experimental set-up and carried out the experiments. Q.W. and E.T.F.R. designed the experimental apparatus and carried out data analysis. B.G. prepared the experimental samples. C.M.W. designed the hologram pattern. G.H.Y. designed the super-oscillatory lens and performed angular spectrum simulations. Q.W., N.I.Z. and J.H.T. co-wrote the paper. All authors discussed the results and edited the manuscript. N.I.Z. and J.H.T. supervised and coordinated all the work.

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The authors declare no competing financial interests.

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