Ultrathin metasurface lenses do things conventional optics can't
Once, the only way to manipulate light was with the use of a transparent glass or plastic lens whose shape and makeup determined such things as focus, magnification, and polarity. However, to incorporate all of these properties in the one optical system required a large and complex collection of multiple lenses to achieve. Now researchers working at NASA's Jet Propulsion Laboratory (JPL) and the California Institute of Technology (Caltech) have created a flat silicon metamaterial lens that manages all of these thing in a microminiaure device that electromagnetically controls the properties of any light passing it.
Using an arrangement of silicon nanopillars organized into a honeycomb pattern to form a "metasurface" able to control the direction and attributes of light waves, the new device may one day be mass-produced using much the same methods employed to create computer chips today.
As such, the researchers believe that applications for their creation may include cutting-edge microscopes, displays, sensors, and cameras that could all take advantage of the superior characteristics of high-quality lenses at a fraction of the price.
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"Currently, optical systems are made one component at a time, and the components are often manually assembled," said Andrei Faraon, an assistant professor of applied physics and materials science at Caltech. "But this new technology is very similar to the one used to print semiconductor chips onto silicon wafers, so you could conceivably manufacture millions of systems such as microscopes or cameras at a time."
When observed using a scanning electron microscope, the metasurface created on the new device shows a collection of low pillars, with elliptical cross sections. By precisely adjusting the diameter of each of these pillars and turning them on their axes, the phase and polarization of the light shone on the device were both able to be manipulated concurrently by the researchers.
Whilst other metasurface lenses have been developed in separate research that are capable of focusing multiple wavelengths of light or improving the resolution of microscopic objects, the JPL/Caltech device alters the phase of incoming light – that is, the relationship between the peaks and troughs of the electromagnetic wave itself – to produce a combined, more powerful light wave. Controlling the phase also provides the device with the ability to accurately focus that wave.
Additionally capable of manipulating the polarization of light, the device may also provide a new platform for the superior operation of microscopes, cameras and displays by allowing the incorporation of wafer-thin metasurface devices in the place of larger and bulkier lens systems.
"If you think of a modern microscope, it has multiple components that have to be carefully assembled inside," says professor Faraon. "But with our platform, we can actually make each of these optical components and stack them atop one another very easily using an automated process. Each component is just a millionth of a meter thick, or less than a hundredth of the thickness of a human hair."
Able to modify the shape of light beams at will, the researchers also claim that the new metasurface optical components could also find use in place of complex and pricey optical systems used to circularize the naturally-elliptic beams generated by semiconductor lasers. The exceptionally small dimensions of these devices could also significantly reduce the size of such systems.
Not yet a commercial reality, the researchers have constructed a small number of the devices for experimental use by collaborating scientists in other areas, and are currently liaising with industry to create metasurfaces for use in the likes of miniature cameras and spectrometers.