The emergence of van der Waals (vdW) materials resulted in the discovery of their high optical, mechanical, and electronic anisotropic properties, immediately enabling countless novel phenomena and applications. Such success inspired an intensive search for the highest possible anisotropic properties among vdW materials. Furthermore, the identification of the most promising among the huge family of vdW materials is a challenging quest requiring innovative approaches. Here, we suggest an easy-to-use method for such a survey based on the crystallographic geometrical perspective of vdW materials followed by their optical characterization. Using our approach, we found As₂S₃ as a highly anisotropic vdW material. It demonstrates high in-plane optical anisotropy that is ~20% larger than for rutile and over two times as large as calcite, high refractive index, and transparency in the visible range, overcoming the century-long record set by rutile. Given these benefits, As₂S₃ opens a pathway towards next-generation nanophotonics as demonstrated by an ultrathin true zero-order quarter-wave plate that combines classical and the Fabry–Pérot optical phase accumulations. Hence, our approach provides an effective and easy-to-use method to find vdW materials with the utmost anisotropic properties.

范德华 (vdW) 材料的出现导致人们发现了其高光学、机械和电子各向异性特性，立即实现了无数新颖的现象和应用。这样的成功激发了人们对 vdW 材料中尽可能高的各向异性特性的深入研究。此外，在众多 vdW 材料中找出最有前途的材料是一项具有挑战性的任务，需要创新的方法。在这里，我们建议采用一种易于使用的方法来进行此类调查，该方法基于 vdW 材料的晶体几何视角及其光学表征。使用我们的方法，我们发现 As ₂ S ₃是一种高度各向异性的 vdW 材料。它表现出高面内光学各向异性，比金红石大约 20%，是方解石的两倍以上，具有高折射率和可见光范围内的透明度，打破了金红石长达一个世纪的记录。鉴于这些优势，As ₂ S ₃开辟了通向下一代纳米光子学的道路，结合了经典和法布里-珀罗光学相位积累的超薄真正零级四分之一波片就证明了这一点。因此，我们的方法提供了一种有效且易于使用的方法来寻找具有最大各向异性特性的 vdW 材料。