Core-modulated long-period fiber gratings formed by heating and stretching

In this paper, we developed and experimentally evaluated a new type of long-period fiber grating. This structure is fabricated by CO2 laser polishing and subsequent heating with an oxyhydrogen flame. Firstly, a single-mode fiber is produced using a high-frequency CO2 laser to form periodic trapezoidal structures. It is then heated with an oxyhydrogen-flame-based fiber optic tapering system to bend the core slightly toward the polished area. The micro-bent cores exhibit strong refractive index modulation, which make the core-modulated LPFG more sensitive to tensile strain. The experimental results show that the proposed sensor exhibits a strain sensitivity as high as 30.43 pm/mu epsilon over the 0-100 mu epsilon range and a temperature sensitivity of 9.29 pm/degrees C. Based on the results of a general theoretical analysis and simulations, we attribute the threshold point of its strain sensitivity to the degree of micro-bending of the core. Furthermore, the structure is low cost and compact and exhibits high mechanical strength and thus can be used in a variety of applications in several fields.