Machine learning has recently been introduced into metasurface design to improve the optimization efficiency. Nevertheless, existing methods are primarily limited to single-objective tasks and often yield suboptimal efficiency. Therefore, this paper proposes a general multi-objective optimization framework based on NSGA-II for the design of VO2 (vanadium dioxide) metasurface absorbers. Results demonstrate that the optimization framework successfully optimizes two different fitness functions (absorptance and operational bandwidth) and exhibits exceptional iterative efficiency, converging rapidly within just 7 iterations, faster than the conventional methods (around 50 iterations). Optimized absorber achieves near-perfect absorption of 99.41% and ultra-wide operational bandwidth of 18.5 THz. The research mechanism shows that the high absorptance stems from the strong mode coupling of FP and LSPP (Localized Surface Plasmon Polariton) modes. The absorber reveals a good impedance matching with the free space, where the real and imaginary parts are close to 1 and 0, which also explains the perfect absorption from the impedance matching perspective. Ultimately, the absorber displays an excellent angle tolerance and polarization-insensitive properties. The proposed efficient multi-objective optimization framework has the potential for the design of achromatic metalenses, sensors, and detectors.
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