High Intrinsic Sensitivity Etched Polymer Fiber Bragg Grating Pair for Simultaneous Strain and Temperature Measurements

A sensing configuration for simultaneous measurement of strain and temperature with enhanced intrinsic sensitivity based on a fiber Bragg grating (FBG) pair with one grating inscribed in the etched and the other in unetched polymer fiber region is demonstrated. A poly (methyl methacrylate) based single-mode polymer fiber is etched to different diameters, and it is observed that etching can lead to change in the material properties of the fiber, such as Young's modulus and thermal expansion coefficient, which can play a vital role in improving its intrinsic sensing capabilities. Thus, exploiting the different strain and temperature sensitivities exhibited by etched and unetched polymer FBGs, strain and temperature can be simultaneously measured with very high sensitivity. Experimental results show that rms deviations of ±8.42 με and ±0.39 °C for strain and temperature, respectively, in a real simultaneous measurement. The effect of individual thermal and strain sensitivity coefficients on measurement accuracy is also analyzed.