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Metal-free metamaterials switch between blocking and transmitting light

ll-chalcogenide nano-grating metasurface. (a) Oblique incidence and (b) cross-sectional scanning electron microscopy images of a 750 nm period grating fabricated by focused ion beam milling in a 300 nm thick amorphous GST film on silica. (c) Numerically simulated distribution of the y-component of electric field in the xz plane, overlaid with arrows denoting the direction and magnitude of magnetic field, for a unit cell of such a grating at resonance [at wavelength λ = 1235 nm for P = 750 nm; slot width s = 130 nm].  Citation: Appl. Phys. Lett. 109, 051103 (2016);

A flash of light is all it takes to convert a metal-free metamaterial from a state that blocks certain wavelengths of light to one that transmits them, according to a study (App. Phys. Lett.2016, DOI: 10.1063/1.4959272). The advance could lead to photonic and optoelectronic devices for use in telecommunications and other areas.

Metamaterials exhibit unnatural properties—for example, the ability to selectively reflect, absorb, or transmit light or sound—by virtue of the geometry of their engineered structures. Many metamaterials are made from metals.

This includes versions that switch between “on” and “off” states in response to electric or thermal stimulus. Because metals generally absorb visible and infrared light, these metamaterials can’t be used in various optical devices.

So Kevin F. MacDonald and coworkers at the University of Southampton used a 300-nm-thick film of germanium antimony telluride (Ge2Sb2Te5), or GST, to make a grating featuring parallel lines of GST, roughly 750 nm wide, spaced apart by 130 nm. GST is a phase-change material widely used in DVDs as a data storage medium.

The grating blocks the transmission of near-IR wavelengths between 1,300 and 1,600 nm. But when irradiated with green laser light, GST switches from amorphous to crystalline, making the grating transparent at these wavelengths.

The team is now working to encapsulate GST between protective layers of ZnS and SiO2, as is done with DVDs, to avoid damaging the grating when it is briefly heated to switch it back to its amorphous state.

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