A novel optical fiber sensor based on a balloon-shaped bent single-mode (BSBS) fiber structure incorporating a long-period grating (LPG) for simultaneous measurement of displacement and temperature is described and experimentally demonstrated. The sensor is fabricated by splicing a BSBS fiber structure based on a Mach-Zehnder interferometer (MZI) with a long-period grating (LPG). The interference dip formed by the BSBS fiber structure is sensitive to external displacement and temperature variation, while that formed by an LPG only depends on temperature, displacement, and temperature and, therefore, can be unambiguously and simultaneously measured by this sensor. Experimental results show that this sensor offers a high displacement sensitivity of -306 pm/μ m over the displacement range of 0-80 μm and a temperature sensitivity of 42.9 pm/°C over the temperature range of 20-45 °C. Due to its high measurement sensitivities, low cost, and good repeatability, this sensor could be a realistic candidate for applications where displacement and temperature need to be measured simultaneously.

In recent years, tapered optical fibers (TOFs) have attracted increasing interest and developed into a range of devices used in many practical applications ranging from optical communication, sensing to optical manipulation and high-Q resonators. Compared with conventional optical fibers, TOFs possess a range of unique features, such as large evanescent field, strong optical confinement, mechanical flexibility and compactness. In this review, we critically summarize the multimode interference in TOFs and some of its applications with a focus on our research project undertaken at the Optoelectronics Research Centre of the University of Southampton in the United Kingdom.

A relative humidity (RH) sensor based on a simple singlemode-side polished multimode-singlemode (SSPMS) fiber hybrid structure is investigated, which is capable of working over a relatively high temperature range, at which many RH sensors based on moisture sensitive material coatings cannot operate. The beam propagation method is used to analyze the light transmission characteristics within the side polished multimode fiber (SPMMF) structure. Experimental results show that the SPMMF surface roughness has a significant influence on the sensor's humidity sensing performance, as a result of the adsorption and desorption of water molecules along the side polished surface. A higher surface roughness results in an increased RH sensitivity. It is concluded that the SSPMS fiber structure based RH sensor can achieve 0.069 dB/%RH within the humidity range of 30 %RH-90 %RH for a temperature range of 70 oC to 90 oC. In addition, the temperature cross-sensitivity has been investigated experimentally. The developed fiber optic sensor in this investigation provides a simple and effective approach for RH measurement in a variety of production applications.

Angle measurement based on heterodyne interferometer has been attracted much research interest and applied in various fields ranging from scientific research to practical engineering. However, a systematic research on the typical heterodyne angular interferometer has not been presented before. This paper mainly focused on the error analysis of the heterodyne angular interferometer and its dynamic measurement performance. The influence of error factors originating from optical configuration, mechanical installation and environmental fluctuations on measurement accuracy is analyzed. Furthermore, the performance of the angle interferometer in measuring dynamic angle, especially for high-frequency angular vibration, is evaluated by using a high-frequency angular vibration system and an interferometric fiber optic gyroscope. Finally, the measurement capability and uncertainty of this angle interferometer are also discussed.

This paper investigated the fabrication of a singlemode-multimode-singlemode fiber structure based on a chalcogenide (As ₂ S ₃ and As _x S _1-x ) multimode fiber sandwiched between two standard silica singlemode fibers using a commercial fiber fusion splicer. The temperature dependence of this hybrid fiber structure was investigated and a first proof of concept showed that the hybrid SMS fiber structure has an average experimental temperature sensitivity of circa 84.38 pm/°C over a temperature range of 20 °C~100°C at the wavelength range around 2 μm. The measured results show a general agreement with numerical simulations based on a guided-mode propagation analysis method. Our result provides a potential platform for the development of compact, high-optical-quality, and robust sensing devices operating at the midinfrared wavelength range.