Manipulating the propagation of mid-infrared (mid-IR) light is crucial for optical imaging, biosensing, photocatalysis, and guiding photonic circuits. Artificially engineered metamaterials were introduced to comprehensively control optical waves. However, fabrication challenges and optical losses have impeded the progress. Fortunately, two-dimensional van der Waals (vdW) materials are alternatives because of their inherent optical properties, such as hyperbolic behavior, high confinement, low loss, and atomic-scale thickness. In this research, we conducted theoretical and numerical investigations on the α-phase molybdenum trioxide, a biaxial vdW material, with patterned graphene to assess the potential of the tunable focusing of mid-IR light. Our proposed method directly alters the path of excited light to focus mid-IR light by negative refraction. Further, the patterned graphene in our design offers enhanced focusing characteristics, featuring a significantly reduced waist diameter with 1/92 of the free-space wavelength, an enhanced beam quality without pronounced field ripples, and a fivefold increase in field intensity. Moreover, our approach significantly preserves the waist diameter of the focused beam while facilitating directional steering. Thus, the focused beam can propagate in a canalized manner toward the desired direction. These advancements lay the foundation for promising applications in planar photonics.

中文翻译：

---

通过范德华晶体上的图案化石墨烯聚焦中红外极化激元

操纵中红外 (mid-IR) 光的传播对于光学成像、生物传感、光催化和引导光子电路至关重要。引入人工设计的超材料来全面控制光波。然而，制造挑战和光学损耗阻碍了这一进展。幸运的是，二维范德华 (vdW) 材料因其固有的光学特性而成为替代品，例如双曲行为、高限制、低损耗和原子级厚度。在这项研究中，我们进行了理论和数值研究α相三氧化钼，一种双轴 vdW 材料，与图案化石墨烯一起评估中红外光可调聚焦的潜力。我们提出的方法直接改变激发光的路径，通过负折射聚焦中红外光。此外，我们设计中的图案化石墨烯提供了增强的聚焦特性，其特点是腰部直径显着减小，自由空间波长为 1/92，光束质量增强，没有明显的场波纹，场强增加了五倍。此外，我们的方法显着保留了聚焦光束的腰部直径，同时促进定向转向。因此，聚焦光束可以以管道化的方式朝期望的方向传播。这些进步为平面光子学的有前景的应用奠定了基础。