The flagship monthly journal of SPIE, Optical Engineering (OE) publishes peer-reviewed papers reporting on research and development in all areas of optics, photonics, and imaging science and engineering.

Based on the analysis and research of the existing intelligent bolt technology, this article proposes a smart bolt based on fiber Bragg grating sensing technology. The bolt design process was systematically introduced, and the physical model of the three-point fixed anti-tail fiber sloshing was given, as well as the corresponding simulation and experimental comparison. The ability to monitor the looseness of the smart bolts was also tested and installed as a smart unit in the fiber-optic smart grid system for monitoring and testing. The wire dancing simulation test machine was used to simulate various practical application conditions, and the effective monitoring performance of the intelligent bolt was verified.

A method of monitoring the transmission line galloping based on fiber Bragg grating (FBG) fitting sensor is proposed and verified by video monitoring method in the overhead transmission line experiment. The proposed method can be used to measure the line tension, the galloping mode and amplitude in horizontal and vertical directions in real-time, simultaneously. The functions of this method were confirmed by the 92 hours transmission line galloping results and the influence of the wind speed and direction to the galloping measurement were also analyzed. Compared with the video monitoring method, it has the advantage of being able to measure the tension and galloping mode of line, higher resolution of galloping amplitude monitoring and real-time monitoring regardless of weather condition. This method can be widely used in transmission line monitoring and has positive significance to promote smart grid.

A unique all-fiber interferometric sensor was proposed and successfully demonstrated efficient low-refractive-index liquid sensing in the range from 1.33 to 1.37, which is compatible with those of bio-liquids. A special silica coreless optical fiber with an open V-groove was used as an optical sensing medium, which provided a high sensitivity for a minute liquid volume in the nanoliter scale. The V-groove fiber (VGF) was serially concatenated between two single-mode fibers (SMFs). The LP₀₁ mode guided along the input SMF excited the higher-order modes in the VGF to generate multimode interference, whose spectrum was transmitted through the output SMF. A single liquid droplet with volume of $\sim 80$ nanoliters wet the entire hydrophilic surface of the VGF, and the transmission spectra shifted corresponding to its refractive index in a very linear manner. The sensor also showed a negligible temperature cross-sensitivity in the range 25°C–75°C, which overlaps with the biological temperature window such that the sensitivity of 159.696 nm per refractive index unit (nm/RIU) remained independent of the temperature variation. Modal properties of VGF were thoroughly analyzed numerically, and detailed processes for the sensor fabrication and sensing experiments were reported.

As a key component in the engine system, silicon nitride igniter’s stable and reliable operation is a necessary condition for the proper functioning of the engine system. However, an online high temperature sensor of silicon nitride igniter inside the engine is absent. This paper presents and demonstrates a novel in-fiber integrated high temperature sensor array with high spatial resolution for online temperature field measurement on a silicon nitride igniter. The sensor array with a series of weak reflectors is written by a femtosecond laser in the core of single-mode fiber. The reflectivity of each reflector can be controlled from 10 ⁻⁵ ~10 ⁻⁸ by adjusting the written power of femtosecond laser. Two adjacent weak reflectors form a compact fiber sensor. The size of a single sensor can be as small as 3–5 mm, so it is able to measure the temperature fluctuation in a space down to several millimeters. The five-sensor-array, with the help of a white light interference demodulation system, can measure high temperature up to 1000°C. Due to the advantages of high reliability, compact construction and simple fabrication, this high temperature sensor array can be widely applied in high temperature sensing applications with space constrains.