Mini laser projector will beam HD video directly onto the retina

Scientists in Japan who have developed a tiny high definition RGB projector are tuning the laser-based device to safely beam images onto the retina of human eyes.

The research presented by the University of Fukui is poised to make an impact on the wearable displays and smart glasses market. 

Their device uses a waveguide-type coupler to produce perfectly aligned RGB output beams from three independent lasers and a microelectromechanical mirror to create high-resolution scanning images. 

University of Fukui researchers are now working with Japanese silicon manufacturer Seiren KST Corp. to commercialise the invention with expectations that it could hit the market in the next 12 months. 

Their latest work, presented at the 27th International Display Workshop (IDW ‘20), created an optical engine by integrating a compact RGB laser module measuring only 8×4×3 mm with a microelectromechanical (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 2D images through laser scanning over the projected area.

One challenging aspect of making the laser module was combining the light beams from three independent laser sources to obtain an RGB output. To achieve this, the scientists used a waveguide-type combiner, where each of the three waveguides receives light from each of the primary colours. Although only the centre green waveguide is connected to the actual optical output, the blue and red light travelling on adjacent dead-end waveguides are passed to the centre waveguide through strategically placed couplers. 

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

Moreover, by using an achromatic lens, an excellent circular focused beam is achieved, while also providing the option to use other lenses to produce collimated beams with larger diameters.

The laser beam scanning module can project 1280×720 colour video by tuning the MEMS driving frequency. It is these characteristics, together with its small size and its potentially low battery consumption, that researchers say make the proposed laser scanning projector a promising device for wearable displays. The research team is now well underway with further tuning required to make it possible to safely project images directly onto the retina of the human eyes.

Assistant Professor Nakao said: “At the University of Fukui, we are trying to stir things up in the wearable display industry by developing smart glasses with optical engine, driver circuit, projector, and battery all integrated in one single device.”

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