Comparison of FWHM and peak power techniques for simultaneous measurement of strain and temperature in FBG sensors

Among the optical fiber sensors, fiber Bragg grating (FBG) has found remarkable attraction and many applications due to its ability to measure all environmental parameters, high accuracy and sensitivity, easy installation, and low price. The sensor’s ability to simultaneous measurement of two environmental (physical) parameters, especially strain and temperature, has made it even more demanding. Recently, two techniques based on full width at half maximum (FWHM) and peak power changes of FBG spectrum have been proposed for simultaneous measurement of temperature and strain that use a uniform FBG on a tilted cantilever beam. In this article, we evaluate and compare both techniques and demonstrate that both are equivalent and have almost similar behaviour but do not have the same applications. We find that at the low strain range the peak power technique is more accurate while at the high strain range the FWHM technique has better accuracy. Therefore, in applications such as monitoring civil structures that have a high strain range, it is better to use the FWHM technique and in some delicate industrial applications with a low strain range, the peak power technique is used.