The paper analyses the constraints related to optical tracking of an HMD with a single commercial binocular stereoscopic optical tracking system and offers an overview of different factors affecting the best active fiducial set-up and marker geometries for reliable tracking with a focus on the rotational accuracy of a marker. Two IR diode models with different emission characteristics were tested as active fiducials and the results were compared to localization accuracy of passive fiducials. In terms of preferable marker geometry, it was found that the area enclosed by the fiducials should be maximized. Thus, due to geometrical constraints, very small marker geometries may not be stable or feasible entirely. Rotational accuracy was analysed for cases when the marker was not directly facing the tracking device and it was found that rotation about one axis introduced errors to the determined orientation in space related to the other axes as well.

Solid-state multi-focal and volumetric technologies highlight the future of 3D-display development. One of the most convenient implementations of multi-focal 3D displays are stacks of transparent liquid crystal displays. In this work, the core element is dissected—a switching optical diffuser element based on cholesteric liquid crystals, playing the role of a transparent display. In the present study, high-speed synchronized optical spectroscopy is used. We analyzed the kinetic and electro-optical characteristics of the diffuser element, the operation of which is based on the switching between diffuse and transparent states of this element. The underlying aim of this study was to investigate ways to improve some of these characteristics. It has been found that the transient peak in the optical transmission during field-off state, which is reducing the intensity of the light scattered by the diffuser element, is likely not associated to the assumed formation of the transient planar state. As the origin of this peak, we suggest a transient state possessing uniform lying helix structure, formed due the material flow taking place in the cell during relaxation of the liquid crystal. The role of the contacting surface’s pre-tilt angle in the switching process of the liquid crystal diffuser was established.

The paper present the key technical details of a multifocal near-eye display concept. Along with an overview of the basic architecture, a particular implementation that utilises a digital light processing (DLP^®) based spatial light modulator as the image source is provided in the study. The investigated approach involves the utilisation of a small-scale volumetric screen formed by a stack of fast-switching optical diffuser elements based on liquid crystal technology. The volumetric screen is illuminated by a rear image projector. To make the whole system functional and small, the challenge lies within the development of integrated control board for the projection modules as well as the synchronization of the DLP^® projector image output to the optical diffuser element switching-cycle. The main difficulty of the development process is accounting for the peculiarities of in-house developed diffuser elements and the off-the-shelf DLP^®, which is the main focus of this paper. There is no direct control over the full set of DLP^® operational parameters, an indirect method for adjusting frame dead time is proposed, showing that an increase in dead time close to 0.3 ms (from 0.3 ms to 0.6 ms in the particular setup) can be achieved without significantly sacrificing image colour depth or quality. Tuneable dead time mitigates the limitations set by the non-instantaneous switching of liquid crystal diffuser elements as longer dead times allow for the removal of image bleeding between frames.