Waveplates are widely used in photonics to control the polarization of light^1,2. Often, they are fabricated from birefringent crystals that have different refractive indices along and normal to the crystal axis. Similar optical components are found in the natural world, including the eyes of mantis shrimp^3,4 and the iridescence of giant clams⁵, fish⁶ and plants⁷. Optical retardation in biology relies on sophisticated self-assembly, whereas man-made systems comprise multiple-layered materials^8,9,10,11. Here we report a discovery that bridges these two design principles. We observe wideband achromatic retardation in the visible and near-infrared (532–800 nm) regions for Cs₄PbBr₆ perovskite crystals embedded with CsPbBr₃ nanocrystals. We explain our observations as matched dispersions of the refractive indices of the ordinary and extraordinary rays caused by the ordered embedding of the nanocrystals in the host. The wideband performance and ease of fabrication of these perovskite materials are attractive for future applications.

^{波片在光子学中被广泛用于控制光1,2}的偏振。通常，它们由沿晶轴和垂直于晶轴具有不同折射率的双折射晶体制成。在自然界中发现了类似的光学元件，包括螳螂虾^3,4的眼睛和巨蛤⁵、鱼⁶和植物⁷的虹彩。生物学中的光延迟依赖于复杂的自组装，而人造系统则包含多层材料^8,9,10,11。在这里，我们报告了一个弥合这两个设计原则的发现。我们观察到 Cs 在可见光和近红外（532-800 nm）区域的宽带消色差延迟嵌入 CsPbBr _{3纳米晶体的4} PbBr ₆钙钛矿晶体。我们将我们的观察解释为由纳米晶体在主体中的有序嵌入引起的普通和非常光线的折射率的匹配色散。这些钙钛矿材料的宽带性能和易于制造对未来的应用具有吸引力。