Assessment of the performance of fibre optic sensor designs based on two FBGs

The paper presents, and compares the performance of, two optical sensing systems each based on a combination of two fibre Bragg gratings (FBGs) and where a simple measurement of transmitted or reflected power provides an alternative to specialist interrogators. In both configurations one of the FBGs acts as a reference whilst the other is used as the measuring element. It is shown that using FBGs with wide spectra results in higher dynamic range. The measurement of strain is used to demonstrate the behaviour of the proposed sensing systems. The performance of the two systems is compared experimentally and discussed with the insight of the simultaneous measurement of the spectra reaching the detector.