Compact RGB Scanning Projector Developed for Wearable Displays and Smart Glasses

Researchers from the University of Fukui, in collaboration with SEIREN KST Corp., a Japanese silicon manufacturer, are preparing to commercialize an image projector for eyewear displays.

The team succeeded in creating an optical engine by integrating a compact RGB module measuring 8 × 4 × 3 mm with a microelectromechanical system (MEMS) mirror. The direction in which the MEMS mirror reflects light from the laser module can be controlled electronically, making it possible to project high-quality 3D images through laser scanning over the projected area.

Diagram of the proposed device and the actual implementation, which is compact and thus suitable for wearable devices. Courtesy of the University of Fukui.

One of the more difficult aspects of the design involved combining the light beams from three independent laser sources to obtain an RGB output. Scientists used a waveguide-type combiner, where each of the three waveguides receives light from each of the primary colors. Only the center green waveguide is connected to the actual optical output — the blue and red light traveling on adjacent dead-end waveguides are passed to the center waveguide through strategically placed couplers.

“The measured efficiency of the combiner was as high as 97%, which represents a loss of only 0.13 dB,” said Akira Nakao, assistant professor at the University of Fukui. “The outputs from the individual RGB lasers end up perfectly aligned thanks to the nature of the waveguide-type combiner.”

The researchers used an achromatic lens to achieve a high-quality circular beam, though the option existed to use other lenses to produce collimated beams with larger diameters. The laser beam scanning module in the research projected 1280 × 720 color video by tuning the MEMS driving frequency.

Beyond virtual and augmented reality for entertainment, the device may support applications in conferencing, surveillance, and remote assisted surgery.

“For now, our unit can be used in laser microscopes, sensors, projectors, and HUD displays, particularly those for novel automobile systems with intelligent driving technology, which are all set to reshape our future,” Nakao said.

The researchers are working to further tune the technology to make it possible to safely project images directly onto the retina of human eyes.