In our Augmented Reality (AR) project, we are investigating the use of a retinal projection display based on the association of pixelated holograms and a dense distribution of waveguides. We study the use of gratings impregnated with liquid crystal to actively extract light from waveguides. We explore two extraction strategies: tuning the refractive index contrast between the grating teeth and grooves to erase the grating diffraction effect, and changing the index of the waveguide cladding to tune the evanescence of the guided mode. Firstly, we present and discuss the measurements of the diffraction efficiency of nano-imprint gratings impregnated with liquid crystal and refractive liquid index. Secondly, we discuss the results of integrated switchable extraction grating of the second strategy.

The development of an ideal optical system to support Mixed Reality and Augmented Reality (AR) applications has raised a lot of interest in the scientific community in the last decades. The perfect device remains an inaccessible target and researchers have to focus on the optimization of some specific behaviors. Several years ago, we introduced a disruptive display concept to push the device integration to the limit, with the suppression of the optical system. This allows the imaging process to be considered in a different way with a specific monitoring of the field of view. With this ‘smart glass’ concept, the glass is the display, and the image is formed directly onto the retina with a combination of refractive and diffractive effects. This conceptual target allowed us to define a technological roadmap to support our development. Technologies involved in this concept concern principally the field of Photonic Integrated Circuits in the visible range, digital/analogic holography and Liquid Crystal devices. We will present the current state of our research with a particular focus on the holographic display element. Recent results related to analogic pixelated hologram recording validate and question both our technological and conceptual approach. We will show images formed by sparse holographic pixel distributions with controlled angular characteristics that demonstrate the mix of refractive and diffractive effects. The transmission behavior of this holographic device will also be analyzed.