Visible to mid-infrared giant in-plane optical anisotropy in ternary van der Waals crystals

• Published in: Nature communications Vol. 14; no. 1; pp. 6739 - 8
• Main Authors: Feng, Yanze, Chen, Runkun, He, Junbo, Qi, Liujian, Zhang, Yanan, Sun, Tian, Zhu, Xudan, Liu, Weiming, Ma, Weiliang, Shen, Wanfu, Hu, Chunguang, Sun, Xiaojuan, Li, Dabing, Zhang, Rongjun, Li, Peining, Li, Shaojuan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 24.10.2023; Nature Publishing Group; Nature Portfolio
• Subjects: 132/122; 140/133; 639/301; 639/624; Anisotropy; Birefringence; Broadband; Crystals; Humanities and Social Sciences; Infrared radiation; multidisciplinary; Photonic crystals; Photonics; Propagation modes; Science; Science (multidisciplinary); Wave propagation; Waveguides; Wavelengths
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-42567-x

Birefringence is at the heart of photonic applications. Layered van der Waals materials inherently support considerable out-of-plane birefringence. However, funnelling light into their small nanoscale area parallel to its out-of-plane optical axis remains challenging. Thus far, the lack of large in-plane birefringence has been a major roadblock hindering their applications. Here, we introduce the presence of broadband, low-loss, giant birefringence in a biaxial van der Waals materials Ta 2 NiS 5 , spanning an ultrawide-band from visible to mid-infrared wavelengths of 0.3–16 μm. The in-plane birefringence Δn ≈ 2 and 0.5 in the visible and mid-infrared ranges is one of the highest among van der Waals materials known to date. Meanwhile, the real-space propagating waveguide modes in Ta 2 NiS 5 show strong in-plane anisotropy with a long propagation length (>20 μm) in the mid-infrared range. Our work may promote next-generation broadband and ultracompact integrated photonics based on van der Waals materials. van der Waals materials are usually characterized by a significant out-of-plane optical anisotropy, but in-plane birefringence is also necessary for photonics applications. Here, the authors report the presence of broadband optical anisotropy in a layered material, Ta 2 NiS 5 , showing in-plane birefringence of ~2 and ~0.5 in the visible and mid-infrared range, respectively.