Self-aligned prism-free fabricated stacked holographic couplers for a full-color augmented reality display

An augmented reality (AR) near-eye display (NED) consists of a display engine and an image combiner, which seamlessly integrate digital content with a real-world environment. A combiner typically comprises couplers and a waveguide that transmits information via total internal reflection (TIR). Volume holographic gratings (VHGs), as waveguide couplers fabricated by laser exposure, are known for their Bragg selectivity and high diffraction efficiency. In this work, a full-color NED with stacked red, green, and blue (RGB) VHGs is fabricated with high diffraction efficiency. Designing a multilayer configuration is a complex process that involves precise fabrication and layer adhesion techniques to avoid alignment errors. However, our recording geometry is much simpler and based on the Bragg degenerate technique, which is prism-free and provides the ease to record self-aligned stacked RGB gratings without any complex layer adhesion technique. The full-color waveguide was successfully fabricated using only two lasers, and a lab prototype was developed to demonstrate the successful propagation of full-color information through the waveguide.