U-shape core-offset fiber sensor with submicrostrain resolution over a 35 millistrain range.

Large strain with submicro resolution is essential for steel structural monitoring; however, the fiber base sensors are limited by the glass extension to be less than 1%. Here, we propose a U-shape core-offset fiber sensor including four fiber segments to realize a large strain sensor. Four fiber segments with slight length differences in between are core-offset fused together to achieve U-shape spring-like microstructure fiber for large transverse bending radius. The reflected high-order modes at three silica/air interfaces interfere to give a broad spectrum due to unequal segment length, which enables continuous strain detection over 35 mɛ. The air and glass hybrid structure of the device enables the large bending, and hence compression and tension measurement can be achieved simultaneously. The strain sensitivity is up to 20.75 pm/µɛ with the strain accuracy of 0.5 µɛ. This novel, to the best of our knowledge, core-offset fiber has high strain sensitivity and large strain range for compression and tension strain measurement. Furthermore, the proposed strain sensor can be fabricated easily for practical applications where large strain with high strain accuracy is needed.