Scientists design new lens to pave way for cutting-edge optical devices

New lens paves way for cutting-edge optical devices

Scientists at the University of Birmingham have designed a new type of lens which is able to switch between convex and concave functions, thereby potentially revolutionising optical device design.

The dual-function, plasmonic metalens has an aperture of 80 micrometers – about the size of a cross-section of human hair – a focal length of 60 micrometers, and has far-reaching implications for imaging systems and silicon chips manufacture.

“This new device will give greater flexibility in designing and adding new functionalities to optical systems as the focusing properties of the same lens can be altered between a convex lens and a concave lens at your will,” said Dr Shuang Zhang, reader in Metamaterials at the University of Birmingham’s School of Physics and Astronomy, and lead investigator of the project.

“Furthermore, the compact size, and the planar nature of the lens could also have an impact on photonic integrated devices,” Dr Zhang said.

The University of Birmingham developed the lens in collaboration with researchers from Paderborn University, Germany, Tsinghua University, China, Hong Kong Baptist University and National University of Singapore. 

It was created by fabricating an array of gold nano-rods on top of glass, thereby allowing for the control of light propagation. Then, by changing the helicity (left- or right-handed rotation of the electric field) of the light shining through the lens, the same lens can function as a concave or convex lens, thereby magnifying or demagnifying objects.

Conventional lens design involves creating a curved surface, while the metalens is 40nm thin on a flat glass surface.

“Conventional lenses have always suffered from optical diffraction limits. These issues can be addressed by the plasmonic metalens. Light can be confined in nano-scale dimensions which are much smaller than the wavelength of photons in free space,” said Hong Minghui, Professor at the Department of Electrical and Computer Engineering, National University of Singapore.

"The planar nature of the lens, according to Minghui, means it “possesses compact features for small form factor and integrated micro/nano photonic devices/chips.”

Lenses are used in cameras, medical imaging, astronomy, optical lithography and integrated circuits, to name a few. So what will the dual nature of the metalens enable these types of devices to do?

“It leads to down scaling of all optical devices. This technology promises higher speed and lower power consumption compared to other semiconductor-based electronic devices. Conventional optics suffers from the diffraction limit, while plasmonics can address such a limit, via guiding and manipulating light to the deep sub-wavelength scale,” explained Prof Minghui.

Prof Minghui also pointed out that the new lens can be produced in large volumes given current mature nanolithography techniques.

As the technology provides the feasibility in the near future to make various, uniquely functional photonic circuits and devices in a small form factor, Prof Minghui said we can expect new products such as “microfluidic devices and in particular optical chips for light computing”.

Because plasmonic waves can carry both electronic and optical signals, the lens can lead to a new version of computing devices which combine the advantages of both nanoelectronic and photonic technologies.

“The technology combines the ultrahigh speed data transfer benefits of fiber optics, with the small size and other advantages of electronic components,”  concluded Prof Minghui.

The research is published in the journal Nature Communications on Tuesday. 

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