Abstract: In this paper, a special microstructured optical fiber based vibration sensor is proposed and experimentally employed in the structural health monitoring of railway. To achieve this, the vibration sensor based on Sagnac interferometer was designed and fabricated. By optimizing the structure of the microstructured optical fiber that has six air holes in the cladding, it could possess high birefringence that changes with the external force applying to the fiber laterally, based on which a linear relationship between the dynamic force and the propagating mode guided in the fiber could be established. Such vibration sensor exhibits a sensitivity of 25 pm/g to acceleration as well as a broad response frequency range. Its resonant frequency is up to over 2 500 Hz, which is dependent on the mechanical design of the sensor package. A field test was conducted using the proposed vibration sensor, and the sensor could measure the large amplitude vibration in low frequency range, as well as those vibrations in high frequency range, which is helpful to identify the corrugations on the rail. The proposed novel vibration sensor based on six-hole microstructured optical fiber provides a new pathway or approach for monitoring the vibration of structures in railway, bridge and mechanical engineering, showing great potential in the applications.

Key words: microstructured optical fiber, vibration sensor, acceleration, structural health monitoring