Compact Dual Fiber Bragg Gratings for Simultaneous Strain and High-Temperature Measurement

We present a compact simultaneous strain and high-temperature measurement scheme using dual fiber Bragg gratings (FBGs) written in single mode fiber (SMF) and thin-core fiber (TCF). The different effective refractive indexes between the cores of SMF and TCF are the key point because such FBGs support two separate resonances in the reflection spectrum for sensing measurement. These two resonances have different optical parameters, elastic-optic coefficient, and thermal-optic coefficient, they shift with different sensitivities under axial strain and temperature variations. The etching process is utilized on the grating of TCF to increase the sensitivity differences of the dual FBGs. In the experiment, simultaneous measurement of strain and temperature with the high strain sensitivity of 3.25 pm/με and high temperature up to 800 °C is realized respectively. This sensor scheme suits the practical application for strain and high-temperature measurement simultaneously.