Researchers from Harvard University have developed a type of metalens that can focus the entire spectrum of light on a single point.
Typically, technology gets smaller and more efficient over time. However, optical lenses — which are in everything from cameras to microscopes — do not follow this rule. That is because researchers have not yet been able to make them more efficient and more compact at the same time.
However, the team in the new study may have gotten around that obstacle with metalenses — tiny, flat devices that use specially engineered nanostructures to focus light. Such lenses mimic the way traditional curved lenses work, but only take up a fraction of the space.
In the research, scientists created a type of metalens that is able to focus the entire visible spectrum of light on single point in high resolution. Before the study, such a feat only occurred when multiple traditional lenses were stacked on top of each other.
It is not easy to focus the entire visible spectrum because each wavelength moves through materials at different speeds. That then causes distortions known as chromatic aberrations. Many optical instruments, such as cameras, get around those issues by using curved lenses with different thicknesses and materials, but that then lowers efficiency.
“Metalenses have advantages over traditional lenses,” said study co-author Federico Capasso, a researcher from the Harvard John A. Paulson School of Engineering and Applied Sciences, according to International Business Times. “Metalenses are thin, easy to fabricate and cost effective. This breakthrough extends those advantages across the whole visible range of light. This is the next big step.”
The new metalenses are paper-thin and have an array of tiny nanostructures made from titanium dioxide. Those structures focus light equally so that all wavelengths arrive at the focal point at the same time and eliminate chromatic aberrations. The design also dramatically reduces thickness and design complexity compared to composite standard lenses.
While the technology is still in the early stages, the quality of images produced with metalenses exceeds those created with traditional lenses. In addition, as they are so small, metalenses are much easier to mass produce than curved ones.
The team next plans to expand on the study by incorporating their new lens into common optical devices, such as cameras, and to scale up the design to about 1 cm in diameter. That could then increase their applications.
“Using our achromatic lens, we are able to perform high quality, white light imaging. This brings us one step closer to the goal of incorporating them into common optical devices such as cameras,” said study co-author Alexander Zhu, a researcher at Harvard University, according to International Business Times.