Optical fiber sensors based on surface plasma technology have many unique advantages in specific applications such as extreme environmental monitoring, physical parameter determination, and biomedical indicators testing. In recent decades, various kinds of fiber probes with special structures were developed according to special processing such as tapering, splicing, etching, fiber balls, grating etc. In this paper, the fabrication technology, characteristics, development status and application scenarios of different special optical fiber structures are briefly reviewed, including common processing equipment. Furthermore, many special novel optical fiber structures reported in recent years are summarized, which have been used in various kinds of plasmonic sensing work. Then, the fiber-plasmonic sensors for practical applications are also introduced and examined in detail. The main aim of this review is to provide guidance and inspiration for researchers to design and fabricate special optical fiber structures, thus facilitating their further research.

Optical fiber sensors based on tapered optical fiber (TOF) structure have attracted a considerable amount of attention from researchers due to the advantages of simple fabrication, high stability, and diverse structures, and have great potential for applications in many fields such as physics, chemistry, and biology. Compared with conventional optical fibers, TOF with their unique structural characteristics significantly improves the sensitivity and response speed of fiber-optic sensors and broadens the application range. This review presents an overview of the latest research status and characteristics of fiber-optic sensors and TOF sensors. Then, the working principle of TOF sensors, fabrication schemes of TOF structures, novel TOF structures in recent years, and the growing emerging application areas are described. Finally, the development trends and challenges of TOF sensors are prospected. The objective of this review is to convey novel perspectives and strategies for the performance optimization and design of TOF sensors based on fiber-optic sensing technologies.

This paper discusses the details about the fabrication of single-mode fiber (SMF)- and multi-mode fiber (MMF)-based core-offset sensor structures for biomolecules detection. SMF-MMF-SMF (SMS) and SMF-core-offset MMF-SMF (SMS structure with core-offset) are proposed in this paper. In the conventional SMS structure the incident light is introduced from the SMF to the MMF and then passes through the MMF to the SMF. However, in the SMS-based core offset structure (COS) the incident light is introduced from the SMF to the core offset MMF and then passes through the MMF to the SMF, and more incident light leaks at the fusion point between the SMF and the MMF. This structure causes more incident light to leak out from the sensor probe, forming evanescent waves. By analyzing the transmitted intensity, the performance of COS can be improved. The results show that the structure of the core offset has great potential for the development of fiber-optic sensors.

Optical fiber sensors based on tapered optical fiber (TOF) structure have attracted a considerable amount of attention from researchers due to the advantages of simple fabrication, high stability, diverse structures, and have great potential for applications in many fields such as physics, chemistry and biology. Compared with ordinary optical fibers, TOF with their unique structural characteristics significantly improve the sensitivity and response speed of fiber-optic sensors and broaden the application range. This review presents an overview of the latest research status and characteristics of fiber-optic sensors and TOF sensors. Then the working principle of TOF sensors, fabrication schemes of TOF structures, novel TOF structures in recent years, and the growing emerging application areas are described. Finally, the development trends and challenges of TOF sensors are prospected. The objective of this review is to convey novel perspectives and strategies for the performance optimization and design of TOF sensors based on fiber-optic sensing technologies.

In this paper, three S-tapered fiber (STF) structures with different diameters (40, 60, and 80 µm) are fabricated using conventional single-mode fiber. First, the reproducibility of the proposed S-tapered structure is confirmed through an analysis of the diameter distribution. Considering the transmitted intensities of the three various diameter, S-tapered structures reveal that the STF with a 40 µm diameter produces more evanescent waves and is more sensitive to external refractive index variations. Therefore, the STF structure with a 40 µm diameter was evaluated for the detection of different concentration of glucose solutions, demonstrating that the structure has the potential to be utilized to develop a highly sensitive fiber sensor.