Concealed Eye-Tracking with Transparent Sensors

 Transparent Electronics Enabled by Graphene and Quantum Dots

Concealed Eye-Tracking with Transparent Sensors

In recent years, the applications of eye-tracking technology have significantly expanded, finding utility in various domains such as virtual reality, augmented reality, automotive safety systems, hands-free computer control, assistive communication devices, and even disease detection.

Traditionally, gaze tracking relied on bulky, non-transparent silicon-based image sensors, positioned at an angle to avoid distracting the user. However, a team of researchers from The Barcelona Institute of Science and Technology, in collaboration with Barcelona-based startup Qurv Technologies, has achieved a breakthrough by developing flexible, nearly transparent image sensors that can be seamlessly integrated into various applications.

These innovative sensors, constructed using graphene and quantum dots, offer the advantage of being directly integrated into items like eyeglasses or curved windshields, positioned conveniently in front of the user's eyes. This advancement not only reduces the bulkiness of eye-tracking hardware but also enhances gaze detection accuracy while decreasing computational complexity. Frank Koppens, co-leader of the research published in ACS Photonics and co-founder of Qurv in 2020, explains the potential impact of this technology, stating, "You have to fantasize. You could have phones or laptops where the entire screen is a sensor to detect hand movements. Mirrors or shop windows could have smart sensors and cameras integrated into the glass to sense human gestures."

Typically, eye-tracking involves emitting infrared light towards the user's eyes and analyzing the reflected signals using image processing algorithms to measure aspects like eye position, movement, and pupil dilation. The existing setup includes light-emitting diodes and one or more infrared cameras mounted away from the user's direct line of sight, such as on the top of VR/AR glasses or along the edges of car windshields.

To create these semi-transparent image sensors, Koppens, along with Qurv Chief Technology Officer Stijn Goossens and their team, combined the unique properties of two nanomaterials. Graphene, an atom-thick material, boasts excellent conductivity and efficient conversion of photons into electrons and positively charged holes but absorbs very little light. In contrast, quantum dots, semiconductor nanocrystals, excel at light absorption.

The researchers deposited graphene on a clear quartz substrate and then coated it with an ultra-thin layer of quantum dots, only a few tens of nanometers thick. The quantum dots absorb photons and transmit them to the graphene, which converts them into an electrical voltage.

These graphene-quantum dot photodetectors maintain a transparency of about 90 percent. While they absorb less light compared to conventional silicon photodetectors, their overall performance remains impressive, with an efficiency of approximately 60 percent, enough for effective eye-tracking.

Koppens notes that the development of such rudimentary photodetectors began a decade ago, and both efficiency and scalability have come a long way since then. They now produce these photodetectors with graphene grown through common vapor deposition techniques on 300-nm wafers.

As a demonstration, the researchers created an 8 x 8 array of graphene-quantum dot photodetector pixels, each measuring 60 x 140 micrometers. These pixels were connected to signal-processing electronics via transparent indium tin oxide wires. The team projected pixelated black and white images onto the array and successfully reconstructed them by reading the signals from each photodetector. Although there is room for improvement, this development marks a significant step forward in transparent image sensor technology.

In the future, the researchers at Qurv plan to enhance the resolution and speed of these image sensors while working on methods to produce them on a larger scale. The potential applications of this technology are extensive, promising a future where everyday objects seamlessly integrate eye-tracking capabilities.