Optical fiber technology has changed the world by enabling extraordinary growth in world-wide communications and sensing. The rapid development and wide deployment of optical fiber sensors are driven by their excellent sensing performance with outstanding flexibility, functionality, and versatility. Notably, the research on specialty optical fibers is playing a critical role in enabling and proliferating the optical fiber sensing applications. This paper overviews recent developments in specialty optical fibers and their sensing applications. The specialty optical fibers are reviewed based on their innovations in special structures, special materials, and technologies to realize lab in/on a fiber. An overview of sensing applications in various fields is presented. The prospects and emerging research areas of specialty optical fibers are also discussed.

We propose an alternative approach to compensation of intermodal interactions in few-mode optical fibers by means of digital backpropagation. Instead of solving the inverse generalized multimode nonlinear Schrödinger equation, we accomplish backpropagation of the multimode signals with help of their near-field intensity distributions captured by a camera. We demonstrate that this task can successfully be handled by a deep neural network and provide a proof of concept by training an autoencoder for backpropagation of six linearly polarized (LP) modes of a step-index fiber.

为进一步加强光缆的运行保护，实现光缆线行区域外力破坏隐患的实时监测，文章利用瑞利后向散射和相干检测原理，设计构建了一种基于分布式光纤振动传感的光缆外破事件监测预警系统。利用相位敏感光时域反射仪（Φ-OTDR）技术，实时采集光纤振动信号，提取振动传感关键性特征，并将隐患类型发送至运维工作人员，对外力破坏隐患进行实时定位和预警。现场验证结果表明：系统能够同时检测和定位沿传感光纤的多个振动源，可以识别出多种类型的扰动信号；该监测预警系统体系完善、架构简单，对各类施工信号的识别率高达95%，实现了外破类型和精确位置的双预警，能够有效预防并制止外力破坏事件。

介质沿空间固定方向均匀分布的结构在电磁导波器件中有十分广泛的应用，对这类器件的分析通常被称为2.5D电磁问题。利用器件在固定方向介质分布均匀的特点，将电磁场量沿该方向进行空间傅里叶变换，可以把对三维问题的分析转化为两维问题求解，从而极大地减小计算开销。针对传统基于差分的2.5D电磁场算法在弯曲形状逼近上有阶梯误差的缺陷，本文提出了基于三角形网格的2.5D时域间断有限元方法（DGTD），并用它模拟了电偶极子与光纤的耦合效率和光子晶体光纤的色散特性。与基于规则网格的2.5D差分方法进行对比。结果表明，文中建立的2.5D DGTD方法对弯曲形状的模拟更加逼真，计算内存占用最大减少10.4%，计算精度最大相差0.011%，计算时间缩短74.9%，计算效率提高。

The flat endface of an optical fiber tip is an emerging light-coupled microscopic platform that combines fiber optics with planar micro- and nanotechnologies. Since different materials and structures are integrated onto the endfaces, optical fiber tip devices have miniature sizes, diverse integrated functions, and low insertion losses, making them suitable for all-optical networks. In recent decades, the increasing demand for multifunctional optical fibers has created opportunities to develop various structures on fiber tips. Meanwhile, the unconventional shape of optical fibers presents challenges involving the adaptation of standard planar micro- and nanostructure preparation strategies for fiber tips. In this context, researchers are committed to exploring and optimizing fiber tip manufacturing techniques, thereby paving the way for future integrated all-fiber devices with multifunctional applications. First, we present a broad overview of current fabrication technologies, classified as “top-down,” “bottom-up,” and “material transfer” methods, for patterning optical fiber tips. Next, we review typical structures integrated on fiber tips and their known and potential applications, categorized with respect to functional structure configurations, including “optical functionalization” and “electrical integration.” Finally, we discuss the prospects for future opportunities involving multifunctional integrated fiber tips.