The expanding role of refractive index measurement in many fields including chemistry, biology and medicine, food industry, process control, and environmental monitoring, has led to a growth of research and development efforts in this field. Optical fibers represents a very promising platform for refractive index sensing due to appealing features such as high sensitivity, small fingerprint, high degrees of integration, compatiblity in harsh environments, and potential to provide real time and remote analysis. Up to date, a wide range of fiber-optic refractive index sensors based on different configurations and mechanisms have been proposed and developed. In this paper, we aim to review the most commonly-used fiber-based refractive index sensors operating in visible and infrared regions, and briefly summarize their advantages and limitations. Furthermore, since THz waves have prominent advantages such as extended probing length, no damage to biological samples, unique fingerprint of biological samples, and non-ionizing feature, we then proceed to review the recent development of several categories of THz waveguide platforms for refractive index sensing applications. Finally, we summarize the review work and present the future perspectives of this field.

折射率测量在化学，生物学和医学，食品工业，过程控制和环境监测等许多领域中的作用日益扩大，导致该领域的研究和开发工作不断增加。光纤由于具有引人注目的功能，例如高灵敏度，小指纹，高集成度，在恶劣环境下的兼容性以及提供实时和远程分析的潜力，因此成为折射率传感的非常有前途的平台。迄今为止，已经提出并开发了基于不同配置和机制的各种光纤折射率传感器。在本文中，我们旨在回顾在可见光和红外区域工作的最常用的基于光纤的折射率传感器，并简要总结其优点和局限性。此外，由于太赫兹波具有突出的优势，例如延长探测长度，对生物样品无损伤，生物样品独特的指纹以及非电离特性，因此我们将着眼于几类太赫兹波导管折射率的最新发展传感应用。最后，我们总结了审查工作，并介绍了该领域的未来前景。