Nanoimprint process to mass manufacture highly-angled high-RI gratings for augmented-reality combiners

Abstract

Blazed and slanted gratings present particularly interesting optical properties in that they can diffract light predominantly into one side of the diffraction plane (m≤0 or m≥0). This is useful in a variety of applications, especially for AR display combiners, where slanted gratings are commonly used to improve efficiency to the eyebox. Nanoimprint lithography (NIL) has been explored as a route to mass manufacture AR waveguides with slanted structures. However, NIL presents several challenges associated with the process of molding and releasing angled features in a high refractive-index, functional material. In this paper we report a series of breakthroughs achieved at Facebook Reality Labs (FRL) that enable replication of gratings with a slant angle up to 60° and an aspect ratio of 10:1 in a material with refractive index higher than 1.90. To the best of our knowledge, these results are the first public demonstration of highly-slanted gratings imprinted in such a RI material.