Twist sensors have emerged as crucial tools in the field of structural health monitoring, playing a significant role in monitoring and ensuring the integrity of critical infrastructure such as dams, tunnels, bridges, pipelines, and buildings. We proposed and demonstrated an all-fiber in-line twist sensor which was based on a capillary fiber spliced between two single-mode fibers with a transverse offset. Through a series of experiments, the sensor’s performance was evaluated and quantified. The results showcased remarkable twist sensitivities in both clockwise and anticlockwise directions. With a transverse offset of 8.0 µm, the sensor exhibited twist sensitivities of −0.077 dB/° and 0.043 dB/° in the clockwise and anticlockwise directions, respectively, in the measured twist range from 0 to 90°. Furthermore, it was also demonstrated that the sensor was temperature insensitive at the chosen wavelength of 1520 nm, which can assist in increasing measurement accuracy. Our sensor’s low cost, simplicity of manufacture, and improved performance will push forward its adoption in future engineering applications such as structural health monitoring in dams, tunnels, and buildings.

Structured illumination microscopy based on phase-shift technique (PS-SIM) has been proposed for precise three-dimensional (3D) reconstruction. In this method, multi frames with pre-defined phase difference are used to calculate the modulation and further determine the 3D shape. Although PS-SIM can reach high measurement accuracy, this method is sensitive to phase-shift error and harmonics caused by digital micro-mirror device (DMD) and camera. In this letter, we propose a method named pixel reassigned structured illumination microscope (PR-SIM), which has the ability to resist harmonics and achieve high measurement accuracy. In this method, the pixels of three phase-shift images are reassigned to generate a new fusion image. After that, two-dimensional Fourier transform is performed on the generated image to obtain the frequency spectrum. In frequency domain, the part of harmonics is effectively separated, and thus precise modulation distribution can be determined. Compared with conventional PS-SIM, this method can effectively suppress the influence of harmonics and achieve accurate measurement. The simulations and experiments are conducted to justify the feasibility of proposed method.