High combiner efficiency and self-aligned compact double-sided diffractive waveguide based on linear surface relief gratings

A diffractive waveguide based on surface relief gratings demonstrates significant potential for augmented reality owing to its ultra-thin and lightweight design, as well as its feasibility for mass production using nanoimprint technology. However, traditional waveguides suffer from low combiner efficiency. To address this issue, we propose what we believe to be a novel double-sided surface relief grating waveguide (abbreviated as double-sided waveguide) with a high combiner efficiency, which comprises a double-sided in-coupler, two single-sided turners, and a double-sided out-coupler. The double-sided in-coupler significantly increases the total in-coupling efficiency, and the turners effectively utilize the dispersed in-coupled energy. The double-sided out-coupler with optimized grating profile parameters minimizes light leakage. The concept has been validated through simulations and experiments. Our results indicate that the fabricated waveguide achieves a central combiner efficiency of 4206 nit/lm under a 30° field of view and 13 mm ×11 mm eye box conditions, exceeding that of traditional diffractive waveguides by more than four times. Additionally, we propose a fabrication method that allows the grating vectors on this waveguide to be self-aligned in a parallelogram. This ensures distortion-free and chromatic-aberration-free image output while simplifying the double-sided nanoimprint fabrication process. These advancements suggest broad potential applications of this waveguide in augmented reality.