This Special Issue focuses on the innovative design of optical fiber sensor structures, including fiber Bragg gratings, long-period gratings, interferometric sensors, and advanced micro-structured fibers. Fiber optic sensors have a real edge over older tech because they don't get messed up by electromagnetic interference, which means they keep collecting good data even when other equipment might go haywire. Another big plus is how these sensors send signals across really long distances without much. Fiber arrays (or fiber optic arrays or fiber array units) are one- or two-dimensional arrays of optical fibers. Often, such an array is formed for only the end of a bundle of fibers, rather than along the entire length of the fiber. Heating the material enables the trapped states to interact with phonons and decay into lower-energy. Optical fiber sensors are renowned for their exceptional sensitivity, compactness, and ability to operate in harsh environments, making them essential in fields such as environmental monitoring, structural health diagnostics, biomedical applications, and industrial process control. The sensing matrix is applied as a film on the fiber end-surface, and consists of poly-methylmethacrylate (PMMA), the oxygen quenchable luminophore platinum-octaethylporphyrin (PtOEP) and the. Fiber-optic sensing (FOS) technology has emerged as a cutting-edge research focus in the sensor field due to its miniaturized structure, high sensitivity, and remarkable electromagnetic interference immunity. Compared with conventional sensing technologies, FOS demonstrates superior capabilities in.