Tunable materials: When this array of optical resonators, made of silver printed on a stretchy polymer, is strained, the filters respond to different frequencies in the infrared spectrum.Credit: Atwater group, Caltech
Metamaterials that could be tuned, rather than working solely in a fixed wavelength, might lead to thermal photovoltaics that change their properties with the weather to maintain high efficiency, goggles that respond to blinding glare to block it out, or devices for processing optical signals to speed telecommunications, for example.
Metamaterial designs are typically limited to operation over a narrow bandwidth dictated by the resonant line width. Here we report a compliant metamaterial with tunability of Δλ 400 nm, greater than the resonant line width at optical frequencies, using high-strain mechanical deformation of an elastomeric substrate to controllably modify the distance between the resonant elements. Using this compliant platform, we demonstrate dynamic surface-enhanced infrared absorption by tuning the metamaterial resonant frequency through a CH stretch vibrational mode, enhancing the reflection signal by a factor of 180. Manipulation of resonator components is also used to tune and modulate the Fano resonance of a coupled system.
Instead of building a metamaterial on rigid materials, the Caltech researchers made an array of silver resonators on a stretchy polymer film. These resonators “ring” when struck with a particular wavelength of light, and act as a strong filter for that wavelength. Each resonator is shaped like a “C” next to an “l”; the distance between the tip of the “C” and the “l,” about 50 nanometers in the test devices, determines the wavelength of light at which it will resonate.