Dixit Saurabh, Sahoo Nihar Ranjan, Mall Abhishek, Kumar Anshuman
Laboratory of Optics of Quantum Materials, Department of Physics, IIT Bombay, Mumbai, Maharashtra, 400076, India.
Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761, Hamburg, Germany.
Sci Rep. 2021 Mar 23;11(1):6612. doi: 10.1038/s41598-021-86056-x.
Mid-infrared (IR) spectral region is of immense importance for astronomy, medical diagnosis, security and imaging due to the existence of the vibrational modes of many important molecules in this spectral range. Therefore, there is a particular interest in miniaturization and integration of IR optical components. To this end, 2D van der Waals (vdW) crystals have shown great potential owing to their ease of integration with other optoelectronic platforms and room temperature operation. Recently, 2D vdW crystals of [Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text] have been shown to possess the unique phenomenon of natural in-plane biaxial hyperbolicity in the mid-infrared frequency regime at room temperature. Here, we report a unique application of this in-plane hyperbolicity for designing highly efficient, lithography free and extremely subwavelength mid-IR photonic devices for polarization engineering. In particular, we show the possibility of a significant reduction in the device footprint while maintaining an enormous extinction ratio from [Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text] [Formula: see text] based mid-IR polarizers. Furthermore, we investigate the application of sub-wavelength thin films of these vdW crystals towards engineering the polarization state of incident mid-IR light via precise control of polarization rotation, ellipticity and relative phase. We explain our results using natural in-plane hyperbolic anisotropy of [Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text] [Formula: see text] via both analytical and full-wave electromagnetic simulations. This work provides a lithography free alternative for miniaturized mid-infrared photonic devices using the hyperbolic anisotropy of [Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text] [Formula: see text].
中红外（IR）光谱区域对于天文学、医学诊断、安全和成像具有极其重要的意义，因为在此光谱范围内存在许多重要分子的振动模式。因此，人们对红外光学元件的小型化和集成特别感兴趣。为此，二维范德华（vdW）晶体因其易于与其他光电平台集成以及室温操作而显示出巨大潜力。最近，已证明[化学式：见原文]-[化学式：见原文]和[化学式：见原文]-[化学式：见原文]的二维vdW晶体在室温下的中红外频率范围内具有自然面内双轴双曲线性的独特现象。在此，我们报告了这种面内双曲线性在设计用于偏振工程的高效、无光刻且极亚波长的中红外光子器件方面的独特应用。特别是，我们展示了在保持基于[化学式：见原文]-[化学式：见原文]和[化学式：见原文]-[化学式：见原文][化学式：见原文]的中红外偏振器高达[化学式：见原文]-[化学式：见原文]和[化学式：见原文]-[化学式：见原文]消光比的同时，显著减小器件尺寸的可能性。此外，我们研究了这些vdW晶体的亚波长薄膜通过精确控制偏振旋转、椭圆率和相对相位来调控入射中红外光偏振态的应用。我们通过解析和全波电磁模拟，利用[化学式：见原文]-[化学式：见原文]和[化学式：见原文]-[化学式：见原文][化学式：见原文]的自然面内双曲线性各向异性来解释我们的结果。这项工作为利用[化学式：见原文]-[化学式：见原文]和[化学式：见原文]-[化学式：见原文][化学式：见原文]的双曲线性各向异性实现小型化中红外光子器件提供了一种无光刻的替代方案。
