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The unique capability of fiber-optic sensors over traditional sensors enables the use of fiber-optic sensing network to realize effective railway monitoring systems. An all-fiber sensing network has many advantages because optical fibers are small, immune from EMI, corrosion free, and has extremely low transmission loss. Interferometric fiber sensors such as fibre Bragg gratings, Fabry-Perot interferometers, and Sagnac loop interferometers can measure a multitude of different physical parameters including strain, acceleration, displacement, and vibration. These are intrinsic sensors and they offer an important unique advantage that the measurands are encoded in wavelength, providing very high signal fidelity. More importantly, it allow the realization of a truly integrated monitoring system, eliminating the need to integrate large number of different conventional monitoring systems, thus improving system maintainability and data manipulation.
Railway systems in Hong Kong and Singapore are using fiber-optic sensing networks to switch from scheduled to condition-based and predictive maintenance to meet the rising expectations from passengers for better and more reliable services. The optical sensing networks are installed on in-service trains and rail tracks to monitor the health of tracks and trains, respectively. In addition to real-time monitoring functions that support the operation of the railway and condition-based maintenance, the system also continuously acquire massive amounts of train and track condition data to provide indispensable information for prognostic maintenance. The train condition monitoring system has successfully detected train structure problems that could cause serious accident. The optical fiber sensing systems installed have proven to be highly reliable and require minimal maintenance.
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