Side Polished Fiber: A Versatile Platform for Compact Fiber Devices and Sensors

Side polished fiber (SPF) has a controllable average roughness and length of the side-polishing region, which becomes a versatile platform for integrating multiple materials to interact with the evanescent field to fabricate all-fiber devices and sensors. It has been widely used in couplers, filters, polarizers, optical attenuators, photodetectors, modulators, and sensors for temperature, humidity, strain, biological molecules, chemical gas, and vector magnetic monitoring. In this article, an overview of the development history, fabrication techniques, fiber types, transmission characteristics, and varied recent applications of SPFs are reviewed. Firstly, the fabrication techniques of SPFs are reviewed, including the V-groove assisted polishing technique and wheel polishing technique. Then, the different types of SPFs and their characteristics are discussed. Finally, various applications of SPFs are discussed and concluded theoretically and experimentally, including their principles and structures. When designing the device, the residual thickness and polishing lengths of the SPF need to be appropriately selected in order to obtain the best performance. Developing all-fiber devices and sensors is aimed at practical usability under harsh environments and allows to avoid the high coupling loss between optical fibers and on-chip integrated devices.