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In this paper, the bending characteristics of a long-period fiber grating (LPFG) in a hollow eccentric optical fiber (HEOF) have been investigated. Two samples fabricated under different laser exposure directions have been studied experimentally. The results show that the HEOF-LPFG can distinguish specific bending directions. The resonant peak shifts linearly with increasing curvature, but its sensitivity is lower than that of the LPFGs in single-mode fibers. In addition, the exposure direction shows a great influence on the bending characteristics due to the asymmetry of the fiber core. Furthermore, the responses of the HEOF-LPFG to temperature, axial strain, and external refractive index have been measured.

Fiber Bragg gratings (FBGs) in a hollow eccentric fiber (HEF) have been proposed and demonstrated experimentally. The single-core and two-core HEF FBGs have been inscribed successfully using KrF excimer laser (248 nm), respectively. The temperature and axial strain sensing properties of the two samples have been measured. The experimental results indicate that the temperature and axial strain sensitivities of the two samples are similar, but they are smaller than that of conventional SMF-FBGs. Furthermore, the bending characteristics of the two-core HEF-FBG strongly depend on the bending direction due to the asymmetry of the fiber. Therefore, the proposed two-core HEF-FBGs facilitate temperature-compensated vector-bending sensing by measuring the difference between peak shifts of the two gratings. In addition, the two-core HEF-FBG can be a promising candidate for achieving two-channel filter since the signal crosstalk between the two cores can be largely eliminated by the central air hole.

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