Spectrally multiplexed Bragg gratings in a multicore optical fiber with seven different cores for directional curvature measurements

•Core difference provides the difference in the Bragg gratings wavelengths.•MFD difference of 5-10.5 um provides Bragg wavelengths difference of 8 nm.•Measurable curvature value increases with increasing of Bragg wavelength difference. Several spectrally multiplexed Bragg gratings were manufactured in a seven-core fiber at the same longitudinal location along the fiber axis using the single UV-writing process with a phase mask. A difference in Bragg grating wavelengths was achieved due to the difference in fiber core parameters. The maximum Bragg grating wavelength difference between all cores of the multicore fiber was 8.66 nm. The effect of bending was studied using six cores with Bragg gratings. The difference in the Bragg gratings spectrum makes it possible to perform this measurement with a single interrogation channel. The bending sensitivity was also studied using the central and one of the side cores with a Bragg grating wavelength difference of 7.14 nm. At given fiber parameters, this wavelength difference makes it possible to measure the volume of curvature up to 120 m−1 without any overlapping of the Bragg gratings spectrum.