Reinforced concrete is a material that is widely used nowadays. The main application form of fiber optic is directly embedding fiber optic materials into concrete structures or sticking them on the surface, which can detect thermal stress and solidification, deflection, bending, and stress and strain. During the solidification of concrete, a temperature gradient is generated inside due to hydration, which may cause thermal stress and crack the structure if the cooling process is uneven. Embedding fiber optic sensors into concrete can monitor the internal temperature changes and control the cooling speed accordingly.
The long-term deflection and bending of concrete components are a mechanical problem of interest. To this end, micro-bending strain fiber optic sensors have been developed to measure structural bending and deflection, and one fiber optic is used to connect the sensors at different positions in the entire structure for simultaneous monitoring, and the position of each sensor can be identified using OTDR. Fiber optic sensors can also detect internal damage to concrete structures. Under normal load, the appearance and development of cracks caused by steel reinforcement preventing drying shrinkage or volume changes caused by temperature can be obtained by measuring the change in optical intensity through the embedded fiber optic.
Bridges are the economic lifeline of a country, and their construction and maintenance are important parts of a country's infrastructure development. Using fiber optic sensor technology to measure vibrations, the main vibration response parameters of bridges such as frequency and amplitude can be obtained. The signal fiber optic is pasted inside the bridge, and it produces vibration response as the bridge vibrates. The output optical phase undergoes periodic changes, and the received light intensity by the photodetector also undergoes periodic changes.
Rock and soil engineering testing has a long-lasting effect, complex environment, time-space limitations, and construction environment constraints, and its testing work has always been a difficult problem to be solved urgently. The currently available conventional testing technology has been proven to be extremely difficult to meet the above testing requirements in long-term engineering applications. However, due to the many excellent characteristics of fiber optic sensors, such as small size, light weight, non-conductivity, fast response, and corrosion resistance, the use of fiber optic sensors as detection tools for rock and soil mechanics engineering has become a research focus for scholars.
Optical fiber sensor technology is also widely used in the military. After more than 30 years of development, fiber optic gyroscope has been widely used in civilian aircraft, drones, and missile positioning and control. Fiber optic hydrophones can be used to collect sound on ships and military vessels and detect increasingly advanced submarines. In recent years, the optical fiber network security warning system based on optical fiber sensor technology has begun to be widely used in border and key areas for defense. Currently, the world's developed countries use a security defense system based on distributed fiber optic sensing network system.