Since Morey et al. in the United States first conducted research on strain and temperature sensors using fiber Bragg gratings in 1989, countries around the world have paid great attention to it and carried out extensive application research. In just over a decade, fiber Bragg gratings have become the fastest-growing technology in the field of sensing and have achieved successful applications in many fields. Such as aerospace, civil engineering, composite materials, petrochemicals and other fields.

1、Applications in civil and water conservancy engineering

Structural monitoring in civil engineering is the most active application field of fiber Bragg grating sensors. The measurement of mechanical parameters is of great significance for the maintenance and health condition monitoring of Bridges, mines, tunnels, DAMS, buildings, etc. By measuring the strain distribution of the above-mentioned structure, the local load and health status of the structure can be predicted. Fiber Bragg grating sensors can be attached to the surface of a structure or pre-embedded in it to simultaneously conduct health checks, impact checks, shape control, and vibration damping checks on the structure, thereby monitoring the defect conditions of the structure. In addition, multiple fiber Bragg grating sensors can be connected in series to form a sensor network for quasi-distributed detection of structures, and the sensor signals can be remotely controlled by a computer.

2、Application in Bridge Safety Monitoring

At present, the field where fiber Bragg grating sensors are most widely applied is the safety monitoring of Bridges. The stay cables of cable-stayed Bridges, the main cables and hangers of suspension Bridges, and the tie rods of arch Bridges are the key load-bearing components of these bridge systems. The prestressed anchoring systems of other civil engineering structures, such as the anchor cables and anchor rods used in structural reinforcement, are also key load-bearing components. The magnitude and distribution of the forces on the above-mentioned force-bearing components most directly reflect the health status of the structure. Therefore, monitoring the force conditions of these components and conducting safety analysis and assessment on this basis are of great significance.

The Beddington Trail Bridge near Calgary, Canada, was one of the earliest Bridges to use fiber Bragg grating sensors for measurement (in 1993). Sixteen fiber Bragg grating sensors were attached to the steel reinforcing rods and carbon fiber composite material bars supported by prestressed concrete for long-term monitoring of the bridge structure. And this was regarded as impossible before. There is A prestressed concrete bridge with a span of 72 meters on the A-4 highway near Dresden, Germany. Meis-sner and others from the University of Dresden embedded Bragg gratings in the concrete prisms of the bridge to measure the basic linear response under loads, and conducted comparative tests using conventional strain measurement instruments. The application feasibility of the fiber Bragg grating sensor has been confirmed. During the construction of the V aux box girder viaduct near Lausanne, Switzerland, the Swiss Stress Analysis Laboratory and the United States Naval Research Laboratory used 32 fiber Bragg grating sensors to monitor the quasi-static strain of the box girder when it was pushed and pulled. The 32 fiber Bragg gratings were distributed at different positions of the box girder, and the signals were demodulated using the scanning method - mooring system.

In June 2003, during the health inspection project of Lupu Bridge led by Professor Shi Jiajun from the Bridge Department of Tongji University, fiber Bragg grating sensors from Shanghai Zishan Optoelectronics were adopted to detect the stress, strain and temperature changes of the bridge under various conditions.

Construction situation: The implementation of the entire inspection project mainly includes three major steps: sensor deployment, data measurement, and data analysis. Eight fiber Bragg grating strain sensors and four fiber Bragg grating temperature sensors were installed on the selected end faces of the Lupu Bridge. Among them, the eight fiber Bragg grating strain sensors were connected in series as one channel, and the four temperature sensors were connected in series as one channel. Then, the data was transmitted through optical fibers to the bridge management office to achieve centralized management of the bridge. The cycle of data measurement is determined according to the owner's requirements. By loading on the bridge deck and using a fiber Bragg grating sensor network analyzer, the dynamic strain test of the bridge is completed.

3、Application in Strain Monitoring of Concrete Beams

In 1989, Mendez et al. from Brown University in the United States first proposed embedding optical fiber sensors in concrete buildings and structures, and described some basic ideas in this research field in practical applications. Since then, universities and research institutions in the United States, the United Kingdom, Canada, Japan and other countries have devoted great efforts to researching the application of optical fiber sensors in intelligent concrete structures.

One very tricky problem encountered during the pouring of concrete structures is: how to avoid damaging sensors and optical cables during the concrete pouring process. Fiber Bragg gratings are usually written on ordinary single-mode communication optical fibers. They are brittle and prone to breakage. To adapt to the extensive characteristics of civil engineering construction, when they are used as sensors to measure the strain of building structures, appropriate protective measures should be taken.

A feasible solution is as follows: After arranging the optical fiber lines of the concrete strain sensors in the steel cage, fix the concrete strain sensors in the steel cage at the predetermined positions with iron wires, etc., and then wrap the middle section with gauze and fix it with tape. For the adhesive type of steel bar strain sensor, an external adhesive layer is generally used for protection.

4、Application in Remote Water Level Measurement

The high-precision optical water level sensor developed on the fiber Bragg grating technology platform is specifically used for the measurement of water levels in rivers, lakes and sewage systems. The accuracy of the sensor can reach ±0.1%F·S. The optical fiber is installed inside the sensor. Due to the periodic change in the refractive index of the optical fiber core, FBG is formed and reflects the optical signal of a certain wavelength that meets the Bragg condition. When the FBG is connected to an elastic diaphragm or other equipment, changes in water level can stretch or compress the FBG. Moreover, the reflection wavelength will change periodically with the refractive index. Then, the change in water level can be monitored based on the offset of the reflected wavelength.

5、Application in Highway Health Inspection

The necessity of highway health monitoring: Transportation is closely related to people and is also a major factor restricting urban development. It can be said that the quality of transportation can directly determine the development destiny of a city. Every year, the state invests a large amount of funds in the construction and maintenance of highways, among which the maintenance cost accounts for a large part. Even so, a large number of roads are still damaged every year. The early damage of roads has become a major disease that affects the performance of the functions of expressways and induces traffic accidents. The damage is generally caused by overloading, speeding of cars and natural reasons, and is also closely related to the quality of road construction. Therefore, it is very necessary to conduct health checks during the construction and usage of highways. Nowadays, highways are generally constructed in three layers: the base layer, the ordinary layer and the asphalt layer. During the construction process, temperature and strain sensors are embedded to obtain the changes in temperature and strain in a timely manner, enabling real-time monitoring of the highway quality. Have a detailed understanding of the characteristics of construction materials and the factors that affect the construction quality.