​Near-eye display technologies are garnering increasing interest as a solution for augmented reality. CEA-Leti is currently working on a breakthrough near-eye display concept that could be integrated into glasses. The researchers are leveraging a technology more frequently used in telecommunications: integrated photonics.

Near-eye devices typically consist of an element that generates images, plus an optical system made up of lenses, which  then projects the images generated close to the eye. In 2018, CEA-Leti researchers came up with a new idea: to project the image directly from the display to the back of the eye. Their proposed solution would eliminate the need for an optical system while opening the door to more compact, ergonomic, and attractive smart glasses. They recently made a major step toward VR glasses that look like regular eyeglasses when they succeeded at developing photonic circuits on transparent substrates—a prerequisite to controlling the trajectory of photons inside the eyeglass lens, central to their new concept.

Here's how they did it: First, silicon nitride waveguides were fabricated on silicon using conventional lithography processes; the waveguides were then transferred to glass using bonding and polishing—a process that requires 67 steps!

Compared to photonic circuits for telecommunications, the researchers reduced the size these new components by a factor of three, so that they could be used to guide light in the visible spectrum (~530 nm), an application that is demanding not only in terms of size, but also finish quality. 

The research led to the development of a transparent photonic circuit prototype that was presented at the international Photonics West conference in San Francisco.