In this work we propose a new type of symmetrical surface relief diffractive grating for waveguide-based Augmented Reality near-eye display system with a wide Field of View (FoV). We demonstrate that by using a dual-mode symmetrical in-coupling system and angular pupil tiling, we can extend the overall horizontal FoV. Our grating coupler is optimized for the second diffraction orders. The proposed concept is validated numerically via full-wave electromagnetic analysis of a 1D diffraction grating. Measurements of the diffraction efficiency of the micro-fabricated prototype are compared with the results of the numerical simulation
“High-uniformity dielectric U-shaped surface relief grating coupler for AR headsets.“, O. Shramkova, V. Drazic, B. Varghese, L. Blondé, V. Brac De La Perriere, V. Allié, SPIE Nanoscience and Engineering, 2021, San Diego, USA.
There are multiple challenges to realize waveguide-based Surface Relief Gratings (SRG) for combiners in Augmented Reality (AR) applications: fabricability, efficiency and diffraction uniformity are among the most important ones. Interdigital develops SRG using Edge Waves (EW) to design highly efficient gratings with a high angular robustness. An EW is generated by a diffraction phenomenon appearing at the interface between two dielectric media and its direction of propagation is controlled by the index ratio between the two media and the direction of the incident plane wave. Combining different edges together, we optimize the elementary geometry, i.e., the building block of an SRG, to diffract into the direction defined by the grating equation, optimizing the power transfer of the incident light into the direction of interest. Our approach enables symmetrical structures with low aspect-ratio, optimized for coupling very efficiently into the first or second order modes, the latter leads to over-wavelength pitch sizes. Moreover, our SRG is designed to angularly tile the exit pupil of the light engine without losses, making our structures adapted to any sort of light engines. Based on our unique design concept, we present in-couplers using two waveguides with a field of view of 130 degrees and RGB operation, and a one waveguide system with 90 degrees of field of view and RGB operation, both with a wafer having also an index of refraction of about 1.7. We believe this will pave the way to new DOE combiners for future AR glasses.
“High-uniformity, high-performance double material dielectric diffractive metagratings.“, Valter Drazic , Oksana Shramkova, Bobin Varghese, Laurent Blondé, Valérie Allié, 1SPIE Photonics West, Augmented, Virtual and Mixed Reality (AR, VR, MR) II, March 2021, San Francisco, USA.