Interferometric interrogation of a multicore fiber, two-axis inclinometer

A two-axis inclinometer is created by affixing a glass capillary tube to the end of a multicore fiber, forming the proof mass of a fiber cantilever. As the sensor tilts, fiber Bragg gratings inscribed in individual cores of the multicore fiber experience strain and are interrogated interferometrically. A phase generated carrier demodulation technique is then used to measure the differential phases between cores. Within a measurement cycle, the instrument reports a maximum phase excursion of ±0.55 mrad, corresponding to a curvature uncertainty of ±3.7×10-4 m-1. The experimental calibration and performance of the sensor are presented.