A Mach–Zehnder interferometer constructed using lateral offset and a long period fiber grating for two-dimensional bending vector sensing

We report a two-dimensional bending vector sensor based on a Mach–Zehnder interferometer (MZI). The device consists of a strong coupling long period fiber grating (LPFG) and a slight-lateral-offset fusion splicing joint which can generate an interference pattern and keep the resonance dip of the LPFG relatively independent at the same time. The exposure orientation of the LPFG is perpendicular to the lateral-offset orientation, making it capable of identifying two-dimensional bending directions and amplitude simultaneously. Two-dimensional bending vector sensing characteristics, especially in the four orthogonal directions based on the new structured MZI, have been experimentally demonstrated. Temperature cross-sensitivity is eliminated using the different sensitivities of the two resonance dips. The device will have great potential in shape sensing applications due to the advantages of its vector sensing capability, low cost and ease of fabrication. (paper)