A compact strain sensor based on M-shaped-core long-period fiber grating

Optical sensors for strain measurement have been significantly concerned due to their unique characteristics of quick response, anti-electromagnetic interference and compact size. In this article, a brand-new type of "M" -shaped core long-period fiber grating (M-LPFG) based on core-modulated method is proposed and experimen-tally testified. By means of side-polishing and high-temperature oxyhydrogen flame heating, the cladding of fiber tends to be circular and the core will bend slightly towards the polished area. The micro-bending core is suffered strong refractive index modulation and this phenomenon also excites the evanescent field adequately. By analyzing the simulated light transmission and the transmission spectrum, considerable degree of micro-bending core is achieved. In the experiment, the proposed sensor with 10 periods (5 mm) displays a high strain sensitivity of-19.05 pm/ li epsilon with range of 0-500 li epsilon , and the temperature sensitivity of which is obtained as 51.16 pm/degrees C. Due to relatively small influence on cladding and self-circularity of structure, the M-LPFG possesses a high mechanical strength. With the above advantages of high sensitivity, compact size, low-cost and strong me-chanical strength, the method of fabricating M-LPFG has great potential in strain measurement.