Abstract
The paper presents selective fiber Bragg grating (FBG) inscription in four-core fiber based on a phase mask scanning method. The inscription factors are systematically investigated, which involves fiber core position and focused laser beam size in fiber, etc. Several specific inscriptions (including individual, dual and all inscriptions) are demonstrated. Two orthogonally positioned cores are selectively inscribed and applied to two-dimension vector bending measurement. The measured bending sensitivities of two FBGs range from -54.3 pm/m-1 to 52.2 pm/m-1 and -53.7 pm/m-1 to 52.8 pm/m-1, respectively. More importantly, it has been revealed that their sensitivities versus bending direction follow regular cosinoidal and sinusoidal distribution. The direction and amplitude of the vector bending can be recovered using measured central wavelength shifts of those two FBGs.
Highlights
Recent years, various multi-core fiber (MCF) devices are proposed, improving the light propagation, transmission capacity and multiplexing features
MCF devices have contributed to the development of optical fiber communication [1,2], fiber laser [3,4], and fiber sensing [5,6,7,8]
In most previous reports, the fiber Bragg grating (FBG) are simultaneously inscribed in all cores of MCF [9,14,16,17,18]
Summary
Various multi-core fiber (MCF) devices are proposed, improving the light propagation, transmission capacity and multiplexing features. In the field of fiber sensing, diverse directional bending sensors based on MCF-FBG have been successfully investigated [14,15,16,17,18] These bending sensors can respond not just to the magnitude and the direction because the spatial positions of the different cores produce a differential strain distribution in the transversal cross section when the fiber is bent. Different inscriptions are feasible via carefully adjusting both the the laser beam size and the spatial distance between the fiber and the phase mask [21] They can fabricate gratings in individual core and multi cores of seven core fiber. In the work reported here, we have proposed and experimentally demonstrated the selective fiber Bragg grating inscription in four-core fiber (FCF) for two-dimension vector bending sensing. The sensor can directly measure two orthogonal principal components of two-dimension bending vector, and the magnitude and direction of original bending can be identified via simple trigonometric analysis
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