J. Eur. Opt. Society-Rapid Publ. 22, 20( 2026) 195
ensuring low inter-band coupling and reduced dispersion. Full-field electromagnetic simulations reveal clear backward-wave propagation and negative refraction consistent with the extracted group velocity and effective refractive index values. These observations provide direct physical validation of the numerical predictions and confirm that the negative-index response originates from the engineered photonic dispersion rather than from resonant or metallic effects.
From a design perspective, the results highlight the originality of the proposed approach: instead of tuning geometric parameters through trial and error, the negative refractive index and bandwidth are achieved through inverse design guided by data-driven models. The strong agreement between predicted and simulated results shows that the method reliably captures the nonlinear relationship between geometry and dispersion. This establishes the framework as a practical and scalable tool for the systematic design of broadband negative-index photonic media.
Acknowledgments
The authors gratefully acknowledge the support of the Scientific and Technological Research Council of Turkey( TÜB ITAK _), Project No. 2209-A / 1919B012461048.
Funding This research received no external funding.
Conflicts of interest The authors have nothing to disclose.
Data availability statement
The data supporting the findings of this study are available from the corresponding author upon reasonable request.
Author contribution statement
Conceptualization, C. A. and B. B. O.; Methodology, B. B. O.; Software, C. A., E. H., and B. B. O.; Formal Analysis, B. B. O. and I. O. A.; Investigation, C. A., E. H., B. B. O., and I. O. A.; Writing – Original Draft Preparation, C. A., E. H., B. B. O., and I. O. A.; Writing – Review & Editing, E. H., B. B. O., andI. O. A.; Visualization, B. B. O. and I. O. A.; Supervision, B. B. O. and I. O. A.; Project Administration, C. A. andB. B. O.
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