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Light fantastic

blue light beams

Tomorrow (16th May 2020) is the International Day of Light. The date marks the first successful operation of a laser, in 1960, by physicist and engineer Theodore Maiman. The International Day of Light is a global initiative, under the auspices of UNESCO, that provides an annual focus for appreciation of light and the role it plays in science, culture and art, education, sustainable development and across fields such as medicine and energy.

15 May 2020

Muriel Cozier

Researchers in the US have developed what they say is a new platform allowing computation to be done with beams of light, so called all-optical computing. The platform is based on a ‘fundamentally new material’ that uses reversible swelling and contracting in a hydrogel under low laser power to change the refractive index.

The hydrogel is made up of a polymer network, swollen with water, and a small number of light-responsive molecules known as spiropyran (similar to the molecule used to tint transition lenses). When light is shone through the gel, the area under the light contracts a small amount, concentrating the polymer and changing the refractive index. When the light is turned off, the gel returns to its original state. So when multiple beams are shone through the material, they interact and affect each other creating an optical logic gate.

‘Though they are separated, the beams still see each other and change as a result,’ said Kalaichelvi Saravanamuttu, an associate professor of Chemistry and Chemical Biology at McMaster University and co-senior author of the study. ‘We can imagine, in the long-term, designing computing operations using this intelligent responsiveness,’

The research team explains that most computation uses hard materials such as metal wires, semiconductors and photodiodes. ‘The idea behind all-optical computing is to remove those hard rigid components and control light with light.  Imagine, for example, an entirely soft circuit free robot driven by light from the sun,’ said Amos Meeks graduate student at the Harvard John A Paulson School of Engineering and Applied Sciences (SEAS) and co-first author of the research which is published in Proceedings of the National Academy of Sciences.

Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science at SEAS and co-senior author of the study said ‘Materials science is changing. Self regulated, adaptive materials capable of optimizing their own properties in response to environment, replace static, energy-inefficient, externally regulated analogues. Our reversibly responsive material that controls light at exceptionally small intensities is yet another demonstration of this promising technological revolution.’

Proceedings of the National Academy of Sciences DOI:10.1073/pnas.1902872117

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