image: a Conventional waveguide couples light into the waveguide through first-order diffraction, resulting in wavelength-dependent deflection angles. b K-vector diagram of the conventional waveguide, showing a smaller overlapping full-color field of view. c Metasurface waveguide achieves achromatic light coupling through higher-order diffraction. d K-vector diagram of the metasurface waveguide, demonstrating a larger full-color field of view.
Credit: by Zhongtao Tian, Xiuling Zhu et al.
Throughout the evolution of AR technology, display systems have consistently aimed for a balance between clarity and compactness. Diffractive waveguides, known for their slim profiles, have become central to AR devices and systems, as being adopted by HoloLens and Meta Orion. However, these systems face a critical challenge: chromatic dispersion, which leads to image distortion. Just like a prism disperses sunlight into a rainbow, different wavelengths of light are deflected to different angles when passing through diffractive waveguides. This dispersion not only limits the field of view but also significantly affects color fidelity, particularly at the edges of the field.
In a new paper published in Light: Science & Applications, a team of researchers led by Professor Xiao Wei Sun from the Southern University of Science and Technology has developed an innovative solution that combines inverse-designed metasurface couplers with a single-layer high-refractive-index waveguide. Metasurfaces, composed of engineered nanostructures, can precisely control the phase, amplitude, and polarization of light. By optimizing the geometry of the metasurface couplers, the team achieved consistent coupling efficiency across the RGB spectrum.
Specifically, the metasurface couplers utilize different diffraction orders (4th, 5th, and 6th) to handle red, green, and blue wavelengths, ensuring uniform deflection angles and eliminating chromatic aberration. This single-layer design not only simplifies manufacturing but also enhances overall system performance compared to traditional multi-layer waveguides.
This groundbreaking research opens a new direction for AR display technology. The achromatic metasurface waveguide not only resolves chromatic aberration but also offers multiple advantages: reduced manufacturing complexity due to its single-layer structure, expanded field of view through high-refractive-index design, and optimized coupling efficiency ensuring superior full-color display quality. These features position it as a promising technology for next-generation AR devices, heralding a new era in AR display technology.
Journal
Light Science & Applications
Article Title
Achromatic metasurface waveguide for augmented reality displays