Monitoring System of Static Strain by using Fiber Bragg Gratings with Optical Frequency Domain Reflectometry

Abstract

Structural health monitoring systems have recently been researched and developed to ascertain the scale, danger level and location of structural damage in order to protect the lives of people from disasters caused by damage to artificial structures such as bridges and from natural disasters such as bedrock collapse. We are involved in a project to construct a wide-area structural health monitoring system using a multi-point fiber Bragg grating (FBG) with optical frequency domain reflectometry (OFDR). This system incorporates multi-point FBGs with the same reflection wavelength, and multi-point FBGs with different reflection wavelengths. By using an optical micro-electro-mechanical systems (MEMS) switch to multiplex these FBGs together, we showed that the reflected wavelengths can be measured in real time. This system is capable of monitoring the reflected wavelength measurement status of the selected channel every 4 seconds (corresponding to the period of the optical frequency sweep). By sequentially switching the optical MEMS switch, it is possible to monitor the time-series variation of reflected wavelengths of all channels. By using this system to perform continuous measurements over a 24-hour period, we also demonstrated the feasibility of performing static strain distribution measurements over a long period.