Multifocal Near-Eye Display: Timing of Optical Diffuser Elements and Synchronization to DLP-Based Projection Microunit

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.