A 12.5 mm soft lens can change its focus when electricity is applied, without a motor or any moving mechanical parts.
The prototype is based on a transparent silicone lens attached to a very thin, stretchable membrane. This membrane carries electrodes that let some of the light through. When an electrical voltage is applied, it stretches in all directions. The lens attached to it then flattens slightly, changing the way it converges light.
To understand the device's potential, just think of a camera lens. Focusing generally requires moving lenses to obtain a sharp image. Here, no optical element moves back and forth. Instead, the shape of the lens itself changes directly, thanks to the deformation of the flexible support behind it.
The challenge was to make electrodes that were conductive, stretchable and transparent enough. The researchers used reduced graphene oxide, a carbon-based material related to graphene. They dispersed it in a liquid and then sprayed it onto the membrane like ink. The resulting layers remain flexible and conduct the current needed for deformation.
However, this method involves a trade-off. A denser layer conducts electricity better and promotes stretching, but it absorbs more light. Tests therefore show that a higher density improves the mechanical response at the cost of transparency. The team consequently chose an intermediate amount of material to build the demonstration lens.
The choice of reduced graphene oxide also addresses a manufacturing constraint. High-quality graphene often requires high-temperature processes that are poorly suited to flexible plastics. The material used here, by contrast, can be prepared as ink and then deposited by spraying. This approach makes it easier to create electrodes directly on a deformable membrane.
The researchers envision this principle for compact optical systems, including adaptive glasses, small cameras and certain medical devices. Before that, they want to make the electrodes more uniform so that more light can pass through. Current transparency remains limited by the imperfect surface of the sprayed layers.