Abstract Sapphire shaped crystals are considered as a favorable material platform of the terahertz (THz) waveguide and fiber optics. Unique physical properties of sapphire, along with advantages of the Edge-defined Film-fed Growth (EFG) technique, yield fabrication of the THz waveguides and fibers with a complex cross-section geometry directly from the Al2O3-melt, where no labour-intensive mechanical processing is required. Wide variability of the as-grown sapphire shaped crystal geometries yields different physical mechanisms of electromagnetic waveguidance. In this review, recent advantages in the THz waveguides and fibers based on the EFG-grown sapphire shaped crystals are discussed. While possessing moderate THz-wave absorbtion and quite high dispersion, flexible sapphire fibers with a simple step-index cross-section geometry yield strong confinement of guided modes in a fiber core due to a high refractive index of sapphire in the THz range. This effect opens novel opportunities of sapphire fibers in high-resolution THz imaging, using the principles of either scanning-probe near-field optical microscopy or optical fiber bundles. In turn, antiresonant and photonic crystal hard hollow-core waveguides demonstrate advanced optical performance, along with wide capabilities in THz endoscopy and sensing in harsh environments. This review highlights that the EFG-grown sapphire shaped crystals hold strong potential in different branches of THz optics.

中文翻译：

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用于太赫兹应用的蓝宝石波导和光纤

摘要 蓝宝石晶体被认为是太赫兹（THz）波导和光纤的有利材料平台。蓝宝石独特的物理特性，以及边缘定义薄膜馈电生长 (EFG) 技术的优势，可直接从 Al2O3 熔体中制造具有复杂横截面几何形状的太赫兹波导和光纤，无需劳动密集型需要机械加工。生长的蓝宝石形状晶体几何形状的广泛可变性产生了不同的电磁波导物理机制。在这篇综述中，讨论了基于 EFG 生长的蓝宝石形状晶体的太赫兹波导和光纤的最新优势。在具有适度的太赫兹波吸收和相当高的色散的同时，由于蓝宝石在太赫兹范围内的高折射率，具有简单阶梯折射率横截面几何形状的柔性蓝宝石光纤在光纤纤芯中产生了很强的导模限制。利用扫描探针近场光学显微镜或光纤束的原理，这种效应为蓝宝石光纤在高分辨率太赫兹成像中开辟了新机遇。反过来，反谐振和光子晶体硬空心波导展示了先进的光学性能，以及在太赫兹内窥镜检查和恶劣环境中传感的广泛能力。这篇综述强调了 EFG 生长的蓝宝石形晶体在太赫兹光学的不同分支中具有强大的潜力。利用扫描探针近场光学显微镜或光纤束的原理，这种效应为蓝宝石光纤在高分辨率太赫兹成像中开辟了新机遇。反过来，反谐振和光子晶体硬空心波导展示了先进的光学性能，以及在太赫兹内窥镜检查和恶劣环境中传感的广泛能力。这篇综述强调了 EFG 生长的蓝宝石形晶体在太赫兹光学的不同分支中具有强大的潜力。利用扫描探针近场光学显微镜或光纤束的原理，这种效应为蓝宝石光纤在高分辨率太赫兹成像中开辟了新机遇。反过来，反谐振和光子晶体硬空心波导展示了先进的光学性能，以及在太赫兹内窥镜检查和恶劣环境中传感的广泛能力。这篇综述强调了 EFG 生长的蓝宝石形晶体在太赫兹光学的不同分支中具有强大的潜力。