# AR Displays: Next-Generation Technologies to Solve the Vergence-Accommodation Conflict
## 6 Summary  
We briefly overviewed the current state and trends in 3D stereoscopic wearable displays. It has become generally accepted that the vergence-accommodation conflict is one of the major hindering factors limiting wide acceptance and commercial success of stereoscopic head-mounted display systems, and that solutions have to be found and introduced as fast as possible. An ultimate solution to this is foreseen to be a holographic-type display, but while it still too challenging for practical implementation and commercialization, alternative methods, also offering corrected VAC and monocular focus cues, have been proposed. Among these methods, multifocal wearable displays are expected to be the most promising and commercialized first.  
LightSpace Technologies have proposed a multifocal display solution based on a volumetric display architecture. At the core of the proposition is an ultra-fast response time liquid-crystal optical diffuser element, which, when stacked, forms a projection volume. By using an ultra-fast image-projection microunit and synchronizing image output with an optical state of the projection volume, image depth planes can be output in a time-multiplexed manner at a very high rate surpassing the flicker fusion frequency. Coupling an eyepiece optic to the projection volume demultiplexes different virtual image depth planes expanded over all usable depth space. This is perceived as a depth-discretized space allowing the user to refocus. By implementing four to six image depth planes and utilizing depth blending, the accommodation of the viewer can be driven virtually continuously. The core technology is highly scalable and, when coupled with conventional beam-splitter-based optical image combiners, can result in a compact competitive footprint of the device. As a proof-of-concept, a virtual reality head-mounted display system based on six image depth planes was demonstrated, yielding 72\({}^{\circ}\) horizontal field-of-view, 6 cpd resolution, and VAC-corrected accommodative range of 3.2 D. A further actual design of an AR wearable system based on optimized component size and conventional beam-splitter-based image combiner has was developed. Still, as with all current next-generation  
Figure 10: A computer assisted design (CAD) model based on a realistic preliminary design showing the attainable footprint of an optical diffuser-based multifocal AR head-mounted display.  
3D display technologies, the important limiting factor directly impacting basic image characteristics (resolution, field-of-view, refresh rate) remains the capabilities of available spatial light modulators. For next-generation 3D display technologies to really become competitive, spatial light modulators with improved resolution, small footprint containing low-power-integrated electronics, and ensuring response times as low as possible are required. The progress in this regard is slow but not principally impossible to achieve substantial advancements, at least in some aspects of SLM technologies.  
Data curation, R.Z.; formal analysis, R.Z., M.N. and A.O.; funding acquisition, K.O. and I.O.; investigation, R.Z., K.O., M.N. and U.G.; methodology, A.O. and K.R.; project administration, K.O.; resources, A.O. and I.O.; software, K.O. and K.R.; supervision, K.O. and I.O.; validation, M.N., U.G. and I.O.; visualization, R.Z.; writing--original draft, R.Z. and K.O.; writing--review and editing, K.O., M.N., A.O. and I.O.  
This work has been supported by the European Regional Development Fund, project No. 1.2.1.1/18/A/006 \"head-mounted display technology research\".  
The authors declare no conflicts of interest.