Although the use of diffractive gratings isn't new per se to bring images in front of the wearer's eyes, the researchers managed to eliminate several issues typically associated with this approach, namely rainbow effects and diffraction patterns due to transmissive diffraction.
It took Dispelix Oy's CEO Antti Sunnari and his team a year and a half of development to come up with an optical solution that can be as thin as 1mm in glass, or a bit thicker in optical-grade plastic (for better mechanical resistance), something that would make smart glasses lighter and more aesthetic.
The whole optical path consists of a nanometre-scale coupling grating receiving the image from a display engine on one end, a single waveguide that routes the light beams via total internal reflection through the lens, and on the other end, an out-coupling nanometre-scale grating that expands the virtual image directly onto the wearer's pupil.
This yields a field of view of 30º, supporting a virtual image equivalent to a 60-inch TV viewed from a distance of three metres, claims Sunnari.
Sunnari didn't want to say much more about the physical features of the nanometre-scale coupling gratings, except that all the know-how is in the grating profile, which may not necessarily be homogeneous across the whole optical coupling area.
"We must adjust the gratings' features for the optical materials being used", he explained.