From waste to important new optical diffuser

Posted on Tuesday 25th March 2014

Optical-diffuserDr Haider Butt was awarded College Best Publication February 2014 for his paper, Devitrite-based optical diffusers.

A waste product from the glass production process could find new use as an optical diffuser, which are used in medical laser treatments, communications systems, and household lighting, according to research from Birmingham in partnership with the University of Cambridge.

A form of crystal that was long considered an unwanted by-product of glass making could find practical use as a cheap and efficient optical diffuser, which are used to scatter and soften light for a range of industrial and household applications.

Devitrite is a crystal which is formed when commercial glass is heat treated for extended periods. As it degrades glass’ performance by making it opaque, it was considered a waste product, and its functional properties were never studied. Improvements in commercial manufacturing of glass in the mid 1950s have now enabled it to be removed from the final product altogether.

However, researchers from the University of Birmingham and University of Cambridge have jointly discovered that far from being fit for the bin, devitrite actually possesses many useful characteristics which could make it suitable for a range of practical applications.

Writing in the journal ACS Nano, the researchers found that the very characteristics which make devitrite unsuitable for commercial glass could make it extremely useful as an inexpensive and efficient optical diffuser.

Devitrite consists of needle-like crystals, formed into fan-like shapes. The tiny spacings between the needles are similar to that of the wavelength of visible light, so when light passes through the devitrite, it scatters the light at wide angles of up to 120 degrees.

Optical diffusers are typically either mass produced by sandblasting glass, resulting in low cost devices which diffuse light in a relatively uniform manner, or more expensive engineered holographic diffusers, which can control the shape of the beam of light.

The devitrite-based diffusers developed by researchers from the Department of Engineering and the Department of Materials Science & Metallurgy diffuse light more broadly than the sandblasted devices, while giving some control over the shape of the beam, at lower cost than the engineered holographic devices.

Devitrite can be produced on a large scale, simply by treating ordinary window glass with heat. The crystals grow into the glass itself, making them much more robust than a simple surface coating. In addition, the high melting point of the glass means that the diffusers can withstand temperatures in excess of 500 degrees C.

These diffusers could be used in a range of practical applications, from medical laser treatments, to optical imaging, or even in everyday household use. For instance, the adoption of high-efficiency LED lighting has been slowed somewhat by the harsh light which LEDs produce. A reproducible, low-cost diffuser on an ordinary LED bulb would help address this issue, resulting in softer, warmer light.

“For years, the properties of this type of glass were not even studied as it was considered an unwanted by-product,” said Dr. Haider Butt. “But by taking a closer look at this ‘waste’ product, we found that it could have a new lease of life with real practical applications.”

The inventors (Dr. Haider Butt from School of Mechanical Engineering, University of Birmingham and   and Dr. Kevin Knowles, Department of Materials Science & Metallurgy, University of Cambridge) are currently developing the technology for commercial use with the assistance of Cambridge Enterprise Ltd.

Image courtesy of Dr Haider Butt