Fig. 1. Simplified diagram of stranded fiber optic cable

Fig. 2. Simulation of strain. (a) Diagram of strain calculation; (b) outer core strain of circular arc optical cable

Fig. 3. Theoretical basis of three-dimensional reconstruction. (a) Three basic vectors; (b) continuous Frenet frame on curve

Fig. 4. Relationship between strain and cable structure. (a) Diagram of the fiber twisting on a micro-segment of a helical multicore fiber; (b) schematic diagram of optical fiber bending

Fig. 5. Cross section of three-core symmetric helically fiber

Fig. 6. Solution model of θ1

Fig. 7. Comparison of effects before and after model improvement. (a) θ1; (b) torsion

Fig. 8. Reconstruction results. (a) Curve 1; (b) curve 2

Fig. 9. Reconstruction error of two curves

Fig. 10. Improvement effect of the model. (a) Reconstruction effect of original model on curve 2; (b) comparison of reconstruction error before and after model improvement

Fig. 11. Relationship between reconstruction error and strain point spacing

Fig. 12. Relationship between reconstruction error and distance from centerline to outer core

Fig. 13. Relationship between reconstruction error and radius of curvature