A new optical metamaterial makes true one-way glass possible

A new approach has allowed Aalto University researchers to create a type of metamaterial that has so far been beyond the reach of existing technologies. Unlike natural materials, Metamaterials And metasurfaces can be tailored to have specific electromagnetic properties, which means scientists can create materials with properties desired for industrial applications.

The magnetic properties of a material can affect how it interacts with light. Image credit: Ihar Faniayeu/University of Gothenburg

The new metamaterial takes advantage of the non-reciprocal magnetoelectric (NME) effect. The NME effect implies a connection between certain properties of a material (its magnetism and polarization) and the different field components of light or other electromagnetic waves. The NME effect is negligible in natural materials, but scientists are trying to increase it using metamaterials and metasurfaces because of the technological potential it will open up.

‘So far, the NME effect is not due to realistic industrial applications. Most of the proposed approaches would work only for microwaves and not for visible light, and could not even be fabricated with available technology,’ he says. Shadi Safi Jizi, a doctoral researcher at Aalto. The team designed an optical NME metamaterial that can be fabricated using conventional materials and nanofabrication techniques with existing technology.

The new material opens up applications that would otherwise require a strong external magnetic field to work – for example, making truly one-way glass. Glass currently sold as ‘one-way’ is only semi-transparent, allowing light to pass in both directions. When the brightness varies between the two sides (for example, inside and outside a window), it acts like one-way glass. But NME-based one-way glass would not require a brightness difference because light can only go in one direction.

‘Imagine having this glass window in your home, office or car. Regardless of the brightness outside, people won’t be able to see anything inside, while you enjoy the best view from your window,’ says Safai. If the technology succeeds, this one-way glass could make solar cells more efficient by blocking the thermal emission that existing cells send back to the sun, reducing the amount of energy they capture.

Source: Aalto University

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