Extraordinary Material

A new material capable of oscillating using absorbed light energy has been developed by engineers studying enhanced structures called metamaterials.

The optically-driven mechanical oscillator, as discussed in a publication in Nature Photonics, oscillates continuously by keeping its optical and mechanical resonances—or “forced vibrations”—in sync. It’s made from metamaterials: composite structures with enhanced properties not typically found in nature. The oscillator resembles a tiny capacitor—roughly the size of a quarter, made of two square plates measuring 500 microns a side. The top plate is a bilayer gold/silicon nitride membrane etched with nanoantennas. The bottom plate is a metal reflector.

Credit: UC San Diego Jacobs School of Engineering

Phys.org discusses the mechanism of the metamaterial. The nanoantennas absorb all of the incoming radiation from light and convert that optical energy into heat. In response, the gold/silicon nitride bilayer bends because gold expands more than silicon nitride when heated. The bending of the bilayer alters the width of the air gap separating it from the metal reflector. This change in spacing causes the bilayer to absorb less light and as a result, the bilayer bends back to its original position. The bilayer can once again absorb all of the incoming light and the cycle repeats over and over again.

Increased Functionality

Ertugrul Cubukcu, lead author of the study, points out that the metamaterials are massively effective at absorbing light. This means that they can function under a broad optical range, that a small source like a LED can set it off.

Feats in engineering like these bring to light many applications. Fei Yi, one of the researchers from Cubukcu’s lab, discussed that the metamaterial optical oscillator greatly simplifies functionalities like light-focusing, spectral selectivity, and polarization control. Conventionally, these processes use bulkier materials like lenses, optical filters, and polarizers. The device can potentially be used as a new frequency reference to accurately keep time in GPS, computers, wristwatches and other devices, researchers said.

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