The overhead power transmission line, as an important component of equipment for long-distance power transmission, is threatened by icing and galloping, which will lead to equipment troubles and cause huge economic loss. Thus, there is a great need for on-line monitoring for transmission lines. Because the photoelectric composite cable, such as optical fiber composite overhead ground wire (OPGW) is widely used, it is possible to introduce distributed optical fiber sensors (DOFS) into transmission line status monitoring. Common schemes based on DOFS usually offer low sensing density and are hard to realize global awareness, while phase sensitive optical time domain reflectometry (Φ-OTDR), as a DOFS that has the characteristic of distributed sensing, is hoping to address the limitation. In this paper, by establishing mathematical models, proposing analytical method, and building demonstration devices to analyze the dynamic strain characteristics of overhead power transmission line, an Φ-OTDR based on-line monitoring scheme of transmission line status is presented and experimentally proved for the first time. The estimation error of sag is less than 5.8% on centimeter scale, and the estimation error of ice thickness is no more than 10.84% on sub-millimeter scale, which gives an accurate description of transmission line status and provides strong support for early warning of transmission line failures.

A novel fiber-optic surface plasmon resonance sensor for detection of $Cu^{2+}$ ions in an aquatic environment is proposed and experimentally demonstrated. The proposed sensor is fabricated by splicing no-core fiber between multimode fibers and then functionalizing the sensor surface with gold film and chitosan (CS)/poly(acrylic acid) (PAA) bilayers. The gold film is used to stimulate surface plasmon waves and make the sensor sensitive to changes in refractive index induced by $Cu^{2+}$ ions absorption on the CS/PAA bilayers. The proposed sensor has a linear relationship between the wavelength shifts and the concentrations of $Cu^{2+}$ ions from 0.2 to 50 μM and 50 to 500 μM, respectively. It is also observed that the sensor's performance is better at low concentrations, and its sensitivity decreases with the increasing concentration. Moreover, we find the proposed sensor can express the self-assembly process between CS and PAA clearly, which shows us a new and easy way to investigate the polyelectrolyte self-assembling.

Phase-sensitive time-domain reflectometry (Φ-OTDR) can be used for fully distributed long-distance vibration monitoring. There is a fading phenolmenon in the Φ-OTDR, which will cause the signal intensity somewhere to be too low to extract the phase of the signal without distortion. In this paper, the Φ-OTDR based on space-division multiplexing (SDM) is proposed to suppress fading and we used multi-core optical fiber (MCF) to realize SDM. While inheriting the previous optimization strategy, we proposed a strategy based on frequency spectral similarity to process multiple independent signals obtained by SDM. And we compared the two methods. Through the experiments, the distortion rate can be reduced from an average level of 9.34% to less than 2% under continuous running of 270 s, which proves that SDM is a reliable technical route to achieve fading suppression. This method can effectively improve the fading suppression capability of the existed commercial systems.

A newly designed phase-locked (PL) Φ-OTDR system was proposed and instrumented. Field tests of water impact, anchor damage towing and tide diagnosing were carried out in a natural freshwater lake as well as the East China Sea. Personnel movement trajectory monitoring and ship flow monitoring were carried out by a buried cable along the floodplain of the Yangtze River. It proved that the proposed system can monitor the real-time status and sense the surrounding environment of existing underwater communication cables, which could be helpful for the maintenance of the cable itself as well as underwater information collection.

As the most common member of the underground pipeline, optical cable has already spread throughout the urban region. By combining the distributed acoustic sensing (DAS) system with the existing optical cables, it is possible to monitor all vibration events around the cable path. DAS data is commonly used to obtain the position of cable section under disturbance and describe the intensity or type of vibration. If the location of the vibration source relative to the optical cable can be further obtained, it will be able to realize the trajectory tracking of the ground target, which would be more conducive to the identification and early warning of external threats to the pipelines. This paper proposes a series of self-optimized methods such as adaptive short-time energy (ASTE), quality factor of fitting (QFF) based fitting optimization, joint localization by multi-samples (JLM), etc., which overcome the influence of the heterogeneous underground medium in field environment, achieving precise localization result on the vibration source with a vertical offset over 60 m. The proposed method provides a promising option for early warning of external threats to these existing underground pipelines without any extra reconstruction work.

This study aimed to evaluate on-water kayak paddling performance using a custom-built instrumented paddle system based on optical fiber technology. The system was developed to measure real-time handgrip loading and blade loading distribution during on-water kayaking. Thirty female participants (15 competitive and 15 recreational kayakers) were asked to sprint across a 50-meter swimming pool as fast as they could in a kayak using the instrumented paddle provided. The loading characteristics of the right handgrip and 9 areas of each blade were recorded and analyzed via a customized software. Noticeable differences in timing and loading variables were observed between the two groups. Compared to recreational paddlers, competitive paddlers were characterized by shorter water phase duration (p < 0.05), higher handgrip loading (p < 0.05), and higher blade force (p < 0.05) and impulse (p < 0.05) in most regions of the blade. In conclusion, this study successfully developed an instrumented paddle system using optical fiber sensors to measure on-water kayak paddling performance. The results can provide useful information for coaches and athletes to obtain performance feedback and to monitor training.