New analysis from Kent State College and Meta Actuality Labs has demonstrated giant dynamic focus liquid crystal lenses which might be used to create varifocal VR headsets.
Vergence-Lodging Battle in a Nutshell
Within the VR R&D area, one of many sizzling matters is discovering a sensible answer for the so-called vergence-accommodation battle (VAC). All client VR headsets available on the market up to now render a picture utilizing stereoscopy which creates 3D imagery that helps the vergence reflex of pair of eyes (once they converge on objects to kind a stereo picture), however not the lodging reflex of a person eye (when the lens of the attention adjustments form to focus gentle at completely different depths).
In the actual world, these two reflexes at all times work in tandem, however in a VR they turn into disconnected as a result of the eyes proceed to converge the place wanted, however their accomodation stays static as a result of the sunshine is all coming from the identical distance (the show). Researchers within the discipline say VAC could cause eye pressure, make it troublesome to concentrate on shut imagery, and should even restrict visible immersion.
In search of a Answer
There have been loads of experiments with applied sciences that might be utilized in varifocal headsets that appropriately assist each vergence & lodging, for example holographic shows and a number of focal planes. But it surely appears none have cracked the code on a sensible, price efficient, and mass producible answer to resolve VAC.
One other potential answer to VAC is dynamic focus liquid crystal (LC) lenses which may change their focal size as their voltage is adjusted. Based on a Kent State College graduate scholar undertaking with funding and participation from Meta Actuality Labs, such lenses have been demonstrated beforehand, however largely in very small sizes as a result of the switching time (how shortly focus will be modified) considerably slows down as dimension will increase.
To succeed in the scale of dynamic focus lens that you simply’d need in case you had been to construct it into a up to date VR headset—whereas maintaining switching time low sufficient—the researchers have devised a big dynamic focus LC lens with a collection of ‘section resets’, which they examine to the rings utilized in a Fresnel lens. As an alternative of segmenting the lens in an effort to cut back its width (as with Fresnel), the section reset segments are powered individually from each other so the liquid crystals inside every section can nonetheless change shortly sufficient to be sensible to be used in a varifocal headset.
A Giant, Experimental Lens
In new analysis introduced on the SID Show Week 2022 convention, the researchers characterised a 5cm dynamic focus LC lens to measure its capabilities and establish strengths and weaknesses.
On the ‘strengths’ facet, the researchers present the dynamic focus lens achieves excessive picture high quality towards the middle of the lens whereas supporting a dynamic focus vary from -0.80 D to +0.80 D and a sub-500ms switching velocity.
For reference, in a 90Hz headset a brand new body is proven to the person each 11ms (90 instances per second), whereas a 500ms switching time is the equal of 2Hz (two instances per second). Whereas that’s a lot slower than the framerate of the headset, it might be throughout the sensible velocity when contemplating the speed at which the attention can alter to a brand new focal distance. Additional, the researchers say the switching time will be elevated by stacking a number of lenses.
On the ‘weaknesses’ facet, the researchers discover that the dynamic focus LC lens suffers from a discount in picture high quality because the view approaches the sting of the lens because of the section reset segments—comparable in idea to the sunshine scattering because of the ridges in a Fresnel lens. The introduced work additionally explores a masking approach designed to cut back these artifacts.
In the end, the researchers conclude, the experimental dynamic focus LC lens gives “presumably acceptable [image quality] values […] inside a gaze angle of about 30°,” which is pretty just like the picture high quality falloff of many VR headsets with Fresnel optics as we speak.
To really construct a varifocal headset from this expertise, the researchers say the dynamic focus LC lens can be used along with a conventional lens to attain the optical pipeline wanted in a VR headset. Exact eye-tracking can be obligatory so the system is aware of the place the person is trying and thus easy methods to alter the main target of the lens appropriately for that depth.
The work on this paper presents measurement strategies and benchmarks exhibiting the efficiency of the lens which future researchers can use to check their very own work in opposition to or establish enhancements that might be made to the demonstrated design.
The complete paper has not but been printed, nevertheless it was introduced by its lead writer, Amit Kumar Bhowmick at SID Show Week 2022, and additional credit Afsoon Jamali, Douglas Bryant, Sandro Pintz, and Philip J Bos, between Kent State College and Meta Actuality Labs.