Technical Papers and Presentations

Liquid crystal displays, despite being a well-established technology since the 1970s, still have a multitude of new applications, one of which is augmented reality head-mounted displays. While these AR-HMD devices have been on the market for about a decade, they continue to suffer from a major drawback - the vergence accommodation conflict. With the increased interest in utilizing this technology in professional settings, where prolonged use may be necessary, it is vital to remedy this conflict which greatly increases fatigue on the eyes and brain. To this end, the use of multiple displays inside the device is employed, however, this creates a new problem - switching time limitation when cycling images between these displays which limits the maximum frame rate. Although when moving to the aligned (transparent) state the switch can be hastened by simply applying a higher voltage at the electrodes, the opposite – switching back to the diffuse state – is not so trivial. One approach which shows promise is using additional electrode structures as those found in fountain-fringe field (FFF) display configurations.[1] These electrodes create a non-aligned electric field which helps rotate the liquid crystal molecules back to the diffuse state. In order to effectively introduce these additional electrodes, their geometry needs to be optimized, along with the dielectric layers surrounding them and the photospacers supporting the cell. COMSOL Multiphysics was chosen for the finite-element method modelling of the configurations and parameters in a twisted nematic (TN) liquid crystal cell. Multiple physics nodes were used in COMSOL. The liquid crystals were modelled using the Oseen-Frank partial differential equation formulation with the Weak Form PDE module, electric fields were generated with the Electrostatics module, while the optical response was modelled with the Electromagnetic Waves module. Structural Mechanics module calculations were performed as well to analyze the cell gap deformation depending on photospacer density. The geometry was 2-dimensional and custom made to approximate the real LC cell. Both stationary and dynamical time-dependent studies have been conducted. The periodic condition employing the translational symmetry of the cell has been used for the LC director field and electromagnetic field calculations, while a full cell (1 mm width) was used for the structural analysis.