To overcome the inherently low temperature sensitivity of fiber Bragg gratings (FBGs) in engineering applications under low-temperature conditions, a sensitivity-enhanced FBG temperature sensor based on a polytetrafluoroethylene (PTFE) encapsulation sleeve was developed. Four adhesive materials—silicone thermal grease, polydimethylsiloxane (PDMS), epoxy resin, and modified acrylic ester—were employed to package the FBG within the PTFE sleeve to improve its temperature sensitivity. Thermal stress simulations of the proposed sensor structure were carried out using COMSOL Multiphysics^® 6.2, and the simulation results showed good agreement with the experimental data. Based on the experimental results, the sensitivity-enhancement effects of PTFE combined with different adhesives, as well as the influences of the PTFE sleeve length and wall thickness, were systematically investigated. The results indicate that, within the temperature range of −35 °C to 15 °C, increasing both the length and thickness of the PTFE sleeve can effectively improve the temperature sensitivity of the sensor. When epoxy resin was used as the encapsulating adhesive, the sensor achieved a maximum sensitivity of 117.4 pm/°C, corresponding to a 13.19-fold increase compared with that of a bare FBG sensor. This sensitivity-enhancing packaging structure significantly improves both the temperature sensitivity and linearity of FBG temperature sensors, while also substantially reducing fabrication costs.

Aerospace and power equipment require precise temperature monitoring in extremely high-temperature environments, which often feature narrow and curved installation spaces. Since traditional thermocouples cannot provide both measurement performance and structural flexibility simultaneously, we propose a flexible fiber Bragg grating (FBG) temperature-sensing array. The sensor features a dual-layer composite packaging structure comprising an inner braided quartz-wool layer and an outer nickel-based alloy tube. Combined with a high-temperature annealing process, the packaged array was evaluated against a WRP-191 reference thermocouple. Over the investigated heating and cooling points up to 1000 °C, the maximum absolute indication error, max|T_FBG − T_ref|, was 2.02 °C and the mean absolute indication error was 1.25 °C. These quantities are comparison errors relative to the reference thermocouple and are not expanded uncertainties. The dual-layer design also allowed a minimum demonstrated bending radius of 22 mm, supporting deployment in confined and curved installation paths.

High-power laser systems impose stringent requirements on the laser-induced damage threshold of optical thin films. Post-deposition thermal annealing has been demonstrated as an effective approach to enhancing the LIDT of HfO₂-based coatings; however, its effects on antireflection coatings—particularly those employing non-quarter-wave designs that offer industrial advantages such as fewer layers and lower fabrication cost—remain insufficiently investigated. In this work, non-quarter-wave HfO₂/SiO₂ multilayer antireflection films were fabricated by ion beam-assisted electron beam evaporation, and the effects of thermal annealing on their laser-induced damage characteristics were systematically investigated. Experimental results show that the effect of thermal annealing between 300 and 700 °C on the laser damage resistance of the antireflection coating is not monotonic: the laser-induced damage threshold rises from 27.6 J/cm² in the as-deposited state to 36.7 J/cm² at 500 °C, an improvement of approximately 33.1%, and then falls at 600 °C and 700 °C, while remaining above the as-deposited value throughout. This non-monotonic behavior originates from a competition between two contributions. On the one hand, the repair of oxygen vacancies, the densification of the film, and the growth of the crystallites continuously reduce the population of initiating absorbers and improve heat dissipation. On the other hand, the penalties arising from the exhaustion of the free volume and from the accumulation of tensile stress accelerate in the upper part of the temperature range, and their influence on the threshold progressively outweighs the gain produced by the former. Annealing at 500 °C is therefore the optimum state determined by this competition.

Silica-based optical fibers suffer radiation-induced attenuation (RIA) in radiation-intensive environments, severely reducing their lifespan. We propose a kinetic model based on the evolution of multiple color centers to accurately simulate defect density and quantitatively characterize RIA. The irradiation experiments were conducted using a Co-60 gamma-ray source at a dose rate of 1.25 Gy/s and a controlled temperature of 10 ± 2 °C, with measurements performed at 1310 nm and 1550 nm wavelengths. The model was experimentally validated using fluorine–germanium co-doped fibers. Fitting results demonstrate high accuracy, with a coefficient of determination (R²) > 0.999, normalized root mean square error (NRMSE) < 0.57%, and mean absolute error (MAE) < 0.74 dB/km. Furthermore, it successfully decouples complex macroscopic RIA signals into distinct transient and steady-state defect pools. This phenomenological decoupling enables band-dependent damage analysis and serves as a baseline for evaluating steady-state degradation of F-Ge co-doped fibers under constant irradiation.