Optical metasurfaces offer high-efficiency and flexible wavefront shaping for near-eye displays, especially in wideband waveguide couplers accommodating RGB primary colors. By leveraging the resonance characteristics of sub-wavelength periodic nanostructures, metasurfaces surpass the limitations of traditional optics that rely on multiple components and mediums. In this study, we propose adjustment of the imaginary parts of the material refractive indices as a new method to achieve balanced first-order diffraction efficiencies among RGB colors over a wide field of view (FOV) in an in-coupling metasurface waveguide coupler. Physical mechanism is investigated deeply and systematically in theory. It is found that nanostructure resonances deflect the wavefront and Poynting vector, significantly enhancing first-order diffraction efficiency, while resonance-enhanced absorption plays a crucial role in balancing the diffraction efficiency of RGB primary colors. First experimental demonstration well confirms the practical feasibility of this method and a uniform first-order diffraction efficiency of approximately 20% is achieved among RGB colors across a FOV as large as ∼30° over a single-piece glass substrate. This research provides insights into the design and mechanisms of metasurface waveguide couplers, advancing our understanding of metasurface-based RGB displays and facilitating further advancements in this field.

中文翻译：

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调整折射率虚部均衡超表面波导耦合器RGB耦合效率

光学超表面为近眼显示器提供高效且灵活的波前整形，特别是在适应 RGB 原色的宽带波导耦合器中。通过利用亚波长周期性纳米结构的共振特性，超表面超越了依赖多种组件和介质的传统光学器件的局限性。在本研究中，我们提出调整材料折射率的虚部作为一种新方法，以在内耦合超表面波导耦合器中在宽视场 (FOV) 上实现 RGB 颜色之间平衡的一阶衍射效率。从理论上对物理机制进行了深入、系统的研究。研究发现，纳米结构共振使波前和坡印廷矢量偏转，显着提高了一级衍射效率，而共振增强吸收在平衡RGB原色的衍射效率方面起着至关重要的作用。首次实验演示很好地证实了该方法的实际可行性，并且在单片玻璃基板上约 30° 的 FOV 中，RGB 颜色实现了约 20% 的均匀一阶衍射效率。这项研究提供了对超表面波导耦合器的设计和机制的见解，增进了我们对基于超表面的 RGB 显示器的理解，并促进了该领域的进一步发展。