Ultra-thin meta lens enables full colour imaging

The first flat lens capable of correctly focusing a large range of colours of any polarisation to the same focal spot without the need for any additional elements has been developed.

Researchers at Colombia University School of Engineering and Applied Science developed the lens which is only a micron thick, but offers the performance of the best compound lens systems.

Associate Professor Nanfang Yu led the study and said: "The beauty of our flat lens is that by using meta-atoms of complex shapes, it not only provides the correct distribution of delay for a single colour of light but also for a continuous spectrum of light.

"And because they are so thin, they have the potential to drastically reduce the size and weight of any optical instrument or device used for imaging, such as cameras, microscopes, telescopes, and even our eyeglasses. Think of a pair of eyeglasses with a thickness thinner than a sheet of paper, smartphone cameras that do not bulge out, thin patches of imaging and sensing systems for driverless cars and drones, and miniaturised tools for medical imaging applications."

The meta-lenses used standard 2D planar fabrication techniques similar to those used for fabricating computer chips. The researchers mention that mass manufacturing these meta-lenses should be simple as they are only one layer of nanostructure, and there is no need to go through the expensive and time-consuming grinding and polishing process.

"The production of our flat lenses can be massively parallelised, yielding large quantities of high performance and cheap lenses," noted Sajan Shrestha, a doctoral student in Yu’s group who was co-lead author of the study. "We can therefore send our lens designs to semiconductor foundries for mass production and benefit from economies of scale inherent in the industry."

"Our design algorithm exhausts all degrees of freedom in sculpting an interface into a binary pattern, and, as a result, our flat lenses are able to reach performance approaching the theoretic limit that a single nanostructured interface can possibly achieve," Adam Overvig, the study’s other co-lead author and also a doctoral student with Yu, said.

"In fact, we’ve demonstrated a few flat lenses with the best theoretically possible combined traits: for a given meta-lens diameter, we have achieved the tightest focal spot over the largest wavelength range."

The study was published by Nature’s Light: Science and Applications.

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