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A displacement monitor with deforming ring is developed to ensure the FBG suspended and to avoid it to be chirped by covering glue. The mechanical analysis provides ring size to ensure suitable BFG wavelength shift extent within detected range. Two pieces of FBG are crosswise fixed on the ring and pre-drawn properly. Rail creep force of high speed railway makes one tense, the other compress. To add these two wavelength shifts, the sensitivity is doubled, and environmental temperature interference is eliminated. Its general error is ±0.25% FS; repeatability is 0.2% FS; resolution is 0.1mm; the temperature error, from -20 to 60Cº, is ±0.45mm in 50mm range.

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In this paper, a high-sensitivity fiber Bragg grating (FBG) tilt sensor using a cantilever-based structure is introduced. Two FBGs are fixed on a specially designed elastomer. One end of the elastomer is connected to the mass block, and the other end is connected to the shell. The principle of the tilt sensor is introduced in detail, and the mathematical model is established. The performance of the sensor is studied. The results show that there is a good linear relationship between the central wavelength difference of the two FBGs and the tilt angle in the range of −5° to 5°. The repeatability of the sensor is good, and the tilt sensitivity can reach 231.7pm/°. The influence of the silicone oil on the damping capacity of the sensor is studied. The results show that the damping capacity of the sensor has been improved by sealing the silicone oil inside the shell of the sensor. The field test is carried out on a pier of an elevated bridge, and the result is good, which verifies the practicability of the sensor.

On the 350km/h high speed railway there is a seamless track switch on a bridge. 32 Fiber Bragg Grating (FGB) gauges are used along the neutral line of the tracks to monitor the strain generated by thermal, geological and vibrational factors, and these FBG strain gauges have the function of strain expansion. Meanwhile other 6 FBG sensors are used to measure the temperature for strain compensating purpose. The Finite Element Analysis method is used to analyze the special shape of the gauges. A testing unit was used to test the FBG gauges and bare FBG on the track samples under measurable pressure and tension. The fixing and encapsulating technology of FBG gauges on the surface of the track and to protect the fiber cable to survive in the harsh conditions are discussed. The strain status of switch tracks could be obtained by processing the data from FBG strain gauges and FBG temperature sensors. The results of measurement showed that in 9 days, the strain in the track shifted 350 με, and the strain curves closely correlated with the temperature curves.