Probing micron-scale distributed contortions via a twisted multicore optical fiber

Continuous measurement of small length scale contortions along an arbitrary path is a highly relevant goal within many branches of engineering and technology. An optical fiber—where the probing light propagates within a confined and shielded region—presents an ideal platform for developing the distributed contortion-sensors. In the past, significant progress has been made in developing optical fiber sensors, but a robust and high-resolution distributed contortion-sensor has not been reported in detail. Here, we report the first distributed measurements of fiber contortions with an ultrahigh sensitivity—≤0.3 μm in the transverse plane, 40 μm longitudinal spatial step size, and ≤8 μm resolution for periodic contortions in the longitudinal plane—via a Bragg-grating-inscribed twisted multicore optical fiber. The results are in excellent agreement with the predictions from the Euler-Bernoulli beam-bending model that relates the applied force with the fiber microcontortions. Our distributed-sensor holds promise for a widespread application within a diverse range of fields including biotechnology, robotics, transportation, geology, and security.