A platform that could potentially be used for all-optical computing has been developed through a collaboration between researchers at McMaster University and the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). The technology brings together an adaptive, light-responsive material developed by the Harvard team with light manipulation and measurement techniques performed at McMaster. The SEAS researchers developed a new material that uses reversible swelling and contracting in a hydrogel. Under low laser power, the refractive index of this material changes in response to the intensity of light. A collaboration between McMaster and Harvard researchers has generated a new platform in which light beams communicate with one another through solid matter, establishing the foundation to explore a new form of computing. Courtesy of McMaster University. The hydrogel is composed of a polymer network that is swollen with water, like a sponge, and a small number of light-responsive molecules whose structure changes in the presence of light. This gives the gel the capability both to contain light beams and to transmit information between them. 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. When multiple beams are shone through the material, they interact and affect each other’s intensity, even at large distances or without their optical fields overlapping. “Though they are separated, the beams still see each other and change as a result,” Kalaichelvi Saravanamuttu, an associate professor at McMaster, said. Typically, light beams broaden as they travel, but the gel is able to contain filaments of laser light along the beams’ pathways through the material, as though the light were being channeled through a pipe. The interaction between the filaments of light can be stopped, started, managed, and read, producing a predictable, high-speed output — a form of information that could be developed into a circuit-free form of computing, Saravanamuttu said. “We can imagine, in the long term, designing computing operations using this intelligent responsiveness,” she said. While the broader concept of computing with light is a developing field, this new technology introduces a promising platform in which light beams can communicate with one another through solid matter. “Not only can we design photoresponsive materials that reversibly switch their optical, chemical, and physical properties in the presence of light, but we can use those changes to create channels of light, or self-trapped beams, that can guide and manipulate light,” McMaster researcher Derek Morim said. “Further study may allow us to design even more complex materials to manipulate both light and material in specific ways.” “Materials science is changing,” Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science at SEAS, said. “Self-regulated, adaptive materials capable of optimizing their own properties in response to environment replace static, energy-inefficient, externally regulated analogs. Our reversibly responsive material that controls light at exceptionally small intensities is yet another demonstration of this promising technological revolution.” The research was published in Proceedings of the National Academy of Science (www.doi.org/10.1073/pnas.1902872117).