Newest Material for Optical Applications

Researchers have been successful in developing a structure that could bring optical advances including ultrapowerful microscopes, computers and solar cells. They have shown how to create the metamaterials without the traditional silver or gold previously required. Using the metals is impractical for industry because of high cost and incompatibility with semiconductor manufacturing processes. The metals also do not transmit light efficiently, causing much of it to be lost. The Purdue researchers replaced the metals with an aluminum-doped zinc oxide (AZO).

This new metamaterial consists of 16 layers alternating between AZO and zinc oxide. Light passing from the zinc oxide to the AZO layers encounters an extreme anisotropy, causing its dispersion to become hyperbolic, which dramatically changes the light's behaviour. The doped oxide brings not only enhanced performance but also is compatible with semiconductors. Metamaterials can be applied in optical microscopes that would make them 10 times more powerful and able to see objects as small as DNA; and also useful in advanced sensors; more efficient solar collectors; quantum computing; and cloaking devices. The AZO also modulate the optical properties of metamaterials by varying the concentration of aluminium in the AZO and also by applying an electric filed to the fabricated metamaterial. This switching ability might usher in a new class of metamaterials that could be turned hyperbolic and non-hyperbolic at the flip of a switch.

This could actually lead to a whole new family of devices that can be tuned or switched. AZO can go from dielectric to metallic. So at one specific wavelength, at one applied voltage, it can be metal and at another voltage it can be dielectric. This would lead to tremendous changes in functionality.

The researcher doped zinc oxide with aluminum, meaning the zinc oxide is impregnated with aluminum atoms to alter the material's optical properties. Doping the zinc oxide causes it to behave like a metal at certain wavelengths and like a dielectric at other wavelengths.

The material has been shown to work in the near-infrared range of the spectrum, which is essential for optical communications, and could allow researchers to harness optical black holes to create a new generation of light-harvesting devices for solar energy applications.

 Current optical technologies are limited because, for the efficient control of light, components cannot be smaller than the size of the wavelengths of light. Metamaterials are able to guide and control light on all scales, including the scale of nanometers, or billionths of a meter.

Unlike natural materials, metamaterials are able to reduce the index of refraction to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material and defines how much the speed of light slows down while passing through a material

Natural materials typically have refractive indices greater than one. Metamaterials, however, can make the index of refraction vary from zero to one, which possibly will enable applications including the hyperlens.

Alternative plasmonic materials such as AZO overcome the bottleneck created by conventional metals in the design of optical metamaterials and enable more efficient devices.