Development of a transmissive phase modulator (SLM) based on Liquid Crystal (LCD) for Virtual and Augmented reality applications (AR/VR)

Published : 8 October 2019

Today, the field of display is increasingly oriented towards applications such as augmented reality headphones (HMD) or head-up vision (HUD. In general, these devices use a micro-screen combined with an optical system for projecting an image on a specific surface in the case of an HUD, or directly on the eye in the case of an HMD. These devices have to provide an image with a very high resolution, all on a very wide angle of view. To meet these two issues, the optics needed is expensive and take too much place which increases the difficulty of integration for a mobile system such as the helmet. To solve this problem an intermediate solution exists, it is to use a system composed of an SLM (phase modulation) integrated into a so-called adaptive optical system. Furthermore, the transmissive feature of the SLM is mandatory and only the transmissive LCD microstructures, by acting on the phase and / or the polarization of the light, can find a wavefront corrector function for adaptive optics.

Adaptive optics projects include, for example, compact, high-resolution, high-resolution lenses based on the concept of eye function (Foveation), where only the part of the useful field is highly defined by acting on the correction of the wavefront via the integrated SLM in the optics.

Previous work has shown that this kind of object requires a technology using complex micro-electronics bricks based on the CMOS report on transparent substrate to obtain transmissive screens.

Our last theoretical study on the subject showed that the LCD screen configuration called IPS for In-Plane Switching, could be adapted to meet our needs. This configuration offers a lot of advantages including that of being easier to implement.

The proposed work is part of a new project in which the first phase will consist of simulating, with specific software, the evolution of the liquid crystal according to the different pixel design and electrode design to define the optimal geometry of the crystal liquid cell. If possible, preference will be given to structures where the liquid crystal does not twist. At the end of this study, the second phase of the project will include the complete realization of a screen with a passive matrix while taking into account the concept of the optimised cell. Finally, to measure the performance of the test cells and the final SLM obtained, the development and implementation of an optical and addressing bench for electro-optical characterization will also be requested.

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