Smart railway traffic monitoring using fiber Bragg grating sensors

Fiber Bragg gratings (FBGs) have already proven their efficiency in axle counting when distributed along a railway track and bring advantages with respect to competing sensors. In this work, two relevant originalities are proposed to broaden the state-of-the-art solutions. First, the strain distribution in the rail cross-section is studied to identify the sensitivity, depending on the charge and the position. Secondly, the sensor head, composed of four wavelength-division-multiplexed FBGs in a single optical fiber, is deployed along the railway and interrogated by a small smart read-out device. Two FBGs are used for the train direction determination and the remaining two bring redundancy to reach safety integrity level (SIL) 4. The smart interrogator has been especially developed for this work and is composed of a vertical-cavity surface-emitting laser (VCSEL) and a photodiode driven by a high-speed microprocessor. The useful information (i.e. the number of counted axles) can be wireless communicated. On-field experiments confirm that this approach offers an easier installation process and a democratization of the technology.