track both the track and the bragg grating s 1 restore quickly such that the shift in the wavelength of the reflected signal by s 1 decreases to zero accordingly and the bragg grating s 1 is then ready for the next tensile strain which may caused by another axle therefore based on the shifts in the wavelengths of the reflected optical signals by the bragg gratings the system 100 is able to ascertain certain situations in the tracks 103 105 and further to monitor the railway the exemplary system 100 can be used to count the number of axles of a passing train by counting the number of successive shifts in the wavelength of optical signal reflected by one of the bragg gating the system 100 is also able to determine the end of the train if it does not detect any shifts in the wavelength during a predetermined period which is designed to be substantially longer than a possible maximum period of time for two adjacent axles to pass through the bragg grating since the physical separation between the axles of a train is generally known the exemplary system 100 may easily ascertain the instantaneous speed of the train by using the period of time taken for successive axles to pass through a particular.