FIG. 1.

(A) Generalized OFDR optical network (B) Illustration of helical cores along a length of fiber with the inset image depicting the sensing triad—labeled 1, 2, and 3—and the core fiber—labeled 0. (C) Typical four-core strain response of the FOSS under pure bending, where the outer cores show sinusoidal strain centered around 0, while the center core remains neutral. (D) Typical four-core strain response of the FOSS under bending and twist, where the center core strain remains neutral, while the average of the outer cores is shifted upward or downward. FOSS, fiber optic shape sensing; OD, outside diameter; OFDR, optical frequency domain reflectometry; SEM, scanning electron microscope. Color images are available online.