Light fantastic

Jon Lawson

Scientists manipulate light to make flat surfaces appear as 3D objects

Scientists have created new 2D nanostructured surfaces that appear as realistic 3D objects – including shading and shadows – using cutting-edge nano-engineering.

The research was carried out by King’s College London alongside the University of Bonn in Germany.

When light hits an object, the colour, texture and shape affect how it is absorbed and reflected, allowing humans to make out the object in front of them.

By altering the surface to change how light is reflected, it is possible to manipulate how it appears.

The researchers developed layered materials, incorporating precisely designed nano-features smaller than the wavelength of light, called metasurfaces. This allowed them to control how light is reflected in highly precise ways, so that a 2D surface reflects light just as a 3D object would.

Borrowing a technique from 3D computer graphics called Normal Mapping, researchers encoded shadow effects into the image, creating 3D images more realistic than holograms or 3D cinema.

As a proof of concept, the researchers fabricated a flat metasurface imitating lighting and shading effects of a 3D cube.

Changing the way we see light

The technique could have huge implications for the optical industries, including in TV screens and photography, as well as in security labels for protecting goods and banknotes from counterfeiting.

Professor Anatoly Zayats of King’s College says: “Metasurfaces are amazing. They open up unprecedented freedom in directing and manipulating light. One might ultimately imagine a TV screen that appears exactly the same as you move around it, or a new movement of 3D art”.

The ability to control light could bring new functionality to small camera lenses.

A flat surface can be made to appear optically convex by designing appropriate metasurface properties.

Future generations of smartphone cameras could use the tiny flat metasurfaces that mimic the properties of sophisticated curved camera lenses, allowing much greater control of angle and depth field.

Metasurfaces could also replace heavy optical lenses in applications such as satellites, where weight and size have a big impact on efficiency.

More immediately, the novel nano-materials can already be used to create unique complex 3D images for security and anti-counterfeiting applications, as well as for new measurement applications requiring precise control of light.

Much more than a hologram

Unlike holograms, which require a coherent light source such as a laser to be viewed, these surfaces manipulate the reflection of normal light so they appear as a realistic 3D object in any light condition and from any angle.

Existing holographic approaches rely on ‘specular reflection’ i.e. the light coming from a particular direction is reflected in a unique outgoing direction, as with a mirror. To achieve dynamic light shading effects, a metasurface design involves ‘diffuse reflection’ – which allows control of its scattering properties so that the image can be seen directly on it.

For the proof of concept, the researchers designed a cube using the normal mapping technique, which was encoded into the metasurface. When illuminated, the metasurface instantaneously ‘computes’ how a 3D representation of the image should look and displays it.

Dr Alexander Minovich, The Royal Society Newton International Fellow at King’s College London, says: “The normal mapping demonstrated with our metasurface is a completely new concept, but it could have very important implications for a wide range of optical industries, both in introducing new functionality and making products smaller and lighter.”

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