Dynamic strain sensing characteristics of superimposed fiber Bragg gratings

This paper proposes a high speed interrogation method for the dynamic and static strain gauge using the time synchronicity of multi-reflection spectrum from superimposed fiber Bragg gratings (FBGs). The superimposed FBGs can provide equidistant space of generated sensing pulse train in time domain during dynamic strain gauge, when a triangular scanning voltage is applied to the tunable filter. Both the interrogation speed and accuracy are improved by combining centroid finding with smooth filtering methods. The interrogation speed of dynamic strain has been enhanced by four times by generating a 2 kHz optical sensing pulse train from a 500 Hz scanning frequency. The interrogation uncertainty and total harmonic distortion (THD) characterization of superimposed FBGs are tested, and less than 4 pm standard deviation is obtained.