philip lelyveld The world of entertainment technology

Tunable-focus lenses enhance see-through augmented reality glasses

... In AR devices, both real world and the virtual must be at the correct focus, so any lens that controls the focal length of the virtual object must do this without disturbing the view of the real world. To solve this, two lenses are required—one sits “eye side” of the waveguide (or equivalent), while the other sits “world side” of it (see Fig. 4).

The eye side or “pull” lens is responsible for focusing the virtual object (by applying +N diopters). Since this also unavoidably changes the focal length of the real world, a second lens on the world-side of the waveguide combiner must be included. This “push” lens is then driven to an equal and opposite lens power (-N diopters) to return the real world to its original focal length. The net effect of these two lenses operating in unison to equal and opposite lens powers is only to adjust the focal length of the virtual object. By combining this with eye tracking, for example, an efficient and comfortable way to adjust focus and reduce VAC can be achieved.

FlexEnable’s manufacturing processes and architectures allow for the creation of tunable-focus LC lenses on optically clear ultrathin plastic. This means that unlike glass LC cells, they are extremely thin (each cell is under 100 µm), lightweight, and can be biaxially curved to fit complex AR optics. ...

See the full story here: https://www.laserfocusworld.com/optics/article/55132443/tunable-focus-lenses-enhance-see-through-augmented-reality-glasses