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Responsive lens changes optical behaviour based on presence of gas

Oksana Smirnova

PhD student Oksana Smirnova from the University of Jena in Germany is investigating optical microlenses made from hybrid glasses (image: Jens Meyer/University of Jena)

A research team from the University of Jena has developed a small optical lens, only a few millimetres in size, whose refractive behaviour changes in the presence of gas.

The advance could lead to more efficient, space-saving, and intelligent sensor technology.

Multi-responsive materials can alter optical properties

With support from the Carl Zeiss Foundation, the Jena team is developing so-called multi-responsive materials. 
In the case of the hybrid glass lens, this means that it refracts light more or less strongly depending on whether gas is absorbed in the lens material.

The ‘intelligent’ behaviour of the micro-lens is enabled by the hybrid glass material from which it is made. The molecular structure of the lens consists of a three-dimensional lattice with cavities that can accommodate gas molecules, thereby affecting the optical properties of the material.

The challenge was to transfer classical glass-forming methods to these special materials.

“The metal-organic frameworks we used here are being researched and developed as materials for gas storage or separation,” said Lothar Wondraczek, Professor of Glass Chemistry at the University of Jena. However, most of these substances decompose when heated and are therefore very difficult to form.

The Jena researchers first had to develop a suitable synthesis process for highly pure materials. They then had to identify the optimal conditions under which the material could be shaped. “We melt the material and then transfer it into a 3D-printed mould, where it is pressed. This process allows us to choose almost any desired shape,” said Oksana Smirnova, doctoral candidate and lead author of a paper published in Nature Communications.

The lens shape was deliberately chosen because even the smallest impurities are noticeable in a lens as they directly affect the optical properties.

Use in logic circuits and sensor technology

This new process now fundamentally allows for a wide variety of shapes and geometries, extending beyond the specific application as micro-lenses, Wondraczek noted: “Because these multi-responsive materials react to multiple influences simultaneously, they could be used for logical circuits, for example.

“This specifically means that two conditions are linked for the observable reaction,”Wondraczek continued. “If a light beam hits the lens and gas is absorbed in the lens material simultaneously, then the light is refracted in a particular way, providing combined feedback.”

Membranes for gas separation, whose optical properties change when gas molecules are present, are also conceivable. Such optical components could be used in sensor technology, making measurement methods more efficient, space-saving, and ‘intelligent.’

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