World´s first city-wide fiber Bragg grating sensing network for railway monitoring

Optical fiber sensing network with the capability to measure multitudes of diverse physical and electrical parameters over wide area along many kilometers of optical fibers could provide a truly Smart Railway System that will herald a safer railway industry with reduced maintenance cost, optimized performance and capacity. The use of scanning (wavelength-tunable) laser together with fiber Bragg grating (FBG)-based sensors provides an excellent technology platform to develop such intelligent railway monitoring system. Over the past decade, FBG-based sensors were developed to measure many parameters that include temperature, strain, acceleration, displacement, vibration, inclination, and magnetic field. In principle hundreds of FBG sensors could be serially connected along a single strand of optical fiber. The reflection wavelengths from FBG-based sensors provide the essential sensing information of the conditions of various critical components of railway systems. In 2007, the first “Smart railway monitoring network” using a scanning laser and about fifty FBG-based vibration sensors to monitor trains traveling along the 35-km East Rail Link connecting Hong Kong to Mainland China was built. The system helps to reduce the maintenance cost of trains, and alleviate potential problems on trains by providing early detection of excessive vibrations due to wheels´ “out-of-roundness”, and/or seizure of axle-box bearings. Since then, FBG sensing systems were installed in four Hong Kong metro lines, the Nanjing section of the 1318-km Beijing-Shanghai High-speed Rail Link and also in the India´s Delhi Airport Metro Express Line. The main technologies applied for the smart railway monitoring system consist of: (1) fiber Bragg grating sensors with appropriate transducers to measure various parameters; (2) scanning fiber laser; and (3) monitoring techniques for axle counting, monitor train vibration, assess wheel profile, measure rail tracks resona- ce, etc. FBG sensing technology has proven to be amazingly versatile for railways, as illustrated by the figures shown below. In Hong Kong, the railway company MTRC, which is one of the world´s leading railways for safety, reliability, customer service and cost efficiency, has widely adopted the technology in various applications. In the third quarter of 2013, Prof. Tam´s group started the installation of the world´s first city-wide FBG sensing network to monitor all trains running in Hong Kong.