Fig. 1. Fiber structure and data acquisition. (a) Fiber cross-section and refractive index profile of the core; (b) data-collection region; (c) traditional design process

Fig. 2. Schematic diagram of segmented analysis of the transmission process of randomly-coupled multi-core fibers

Fig. 3. Flow chart of the proposed algorithm-assisted NN forward design method

Fig. 4. Process of PSO-RF

Fig. 5. Pseudocode of the SSA-RF algorithm

Fig. 6. Model prediction effect. (a) Confusion matrix of model NN 1 test for Λ; (b) correlation graphs between actual data and predicted data to evaluate the design accuracy of SMD; (c) comparison between actual and predicted fiber performance

Fig. 7. Schematic diagram of 3-mode 19-core fiber with the circularly symmetrical arrangement. (a) Circular arrangement structure of a 19-core fiber; (b) refractive index profile of a trench-assisted graded-index core in the 3-mode 19-core fiber

Fig. 8. Relationships between structure parameters and κ. (a) Relationship between r₁ and κ; (b) relationship between r₂ and κ; (c) relationship between w₁ and κ; (d) relationship between Δ₁ and κ; (e) relationship between α and κ; (f) relationship between Λ and κ

Fig. 9. Relationships between structure parameters and both DMGD and A_eff. (a) Relationship between r₁ and both DMGD and A_eff ; (b) relationship between r₂ and both DMGD and A_eff; (c) relationship between w₁ and both DMGD and A_eff; (d) relationship between Δ₁ and both DMGD and A_eff; (e) relationship between α and both DMGD and A_eff; (f) relationship between Λ and both DMGD and A_eff

Fig. 10. Inverse design process of few-mode multi-core fiber. (a) Flowchart of two machine learning algorithms combining NN 2 with the PSO algorithm and NN 3; (b) trained NN 2 structure; (c) trained NN 3 structure

Fig. 11. Model prediction effect. (a) Pearson correlation coefficient comparison between NN 2 and NN 3+PSO algorithms; (b) bending loss calculation results of structural parameters obtained by NN 2 and NN 3+PSO algorithms at a wavelength of 1550 nm and R of 140 mm