The path to the construction of contact lenses that will provide night vision to their wearer is being paved by the work of researchers at the University of Michigan, who have created the first room-temperature light that can perceive the full infrared spectrum.
Unlike similar sensors currently on the market, this sensor does not require bulky cooling equipment to operate.
"We can make the whole design extremely thin," said Zhaohui Zhong, assistant professor of electrical/mechanical-computer engineering. "It can be placed in a contact lens or integrated into a mobile phone.".
Infrared light starts at wavelengths slightly longer than visible red light, and extends to wavelengths as long as one millimeter. Infrared vision is best known for its use in detecting people and animals in the dark, as well as heat leaks, but it can also be used to monitor blood flow, detect chemicals in the environment, and other purposes.
Unlike the visible spectrum, which conventional cameras "see" with a chip, infrared vision requires a combination of technologies. The sensors also need to be at very low temperatures.
Graphene was the key here, allowing detection of the entire infrared spectrum, plus visible and ultraviolet light. However, until now it has not been viable for use in the field because it cannot capture enough light to produce a detectable electrical signal.
"The challenge for the current generation of graphene-based sensors is that their sensitivity is low—a hundred to a thousand times lower than what a commercial device would require," says Zhong.
Zhong and Professor Gerard Mourou worked with students to design a new way to generate an electrical signal. Instead of trying to directly measure the electrons released when light hits graphene, they magnified the signal by instead looking at how the electrical charges induced by light in graphene affect a nearby current.
"Our work is a pioneering work in light detection. Our vision is that this mechanism can be adopted in other platforms, materials and devices," adds Zhong.
The resulting device is already smaller than a fingernail, and it can be further scaled down. "If we integrate it into a contact lens or other wearable devices, it expands vision. It provides another way to interact with the environment," the professor adds.
The device is described in detail in a paper titled “Graphene photodetectors with ultra-broadband and high responsivity at room temperature” published in Nature Nanotechnology.
