Inverse-designed non-volatile phase change varifocal metalens at the edge of the visible spectrum

Subrahmanyam S. G. Mantha; Harish N. S. Krishnamoorthy

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arXiv · 2604.00760

Inverse-designed non-volatile phase change varifocal metalens at the edge of the visible spectrum

Subrahmanyam S. G. Mantha·Harish N. S. Krishnamoorthy

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Abstract

Reconfigurable metalenses capable of large focal length tuning, fast response times, and high focusing efficiency while maintaining diffraction-limited operation are highly desirable for next-generation adaptive imaging systems. Phase change chalcogenides provide a promising platform for such devices by exploiting the reversible amorphous-to-crystalline transition to achieve non-volatile tuning with relatively fast switching. However, extending these approaches towards the visible spectrum is challenging because of the reduced meta-atom dimensions, stringent phase coverage requirements, intrinsic material absorption and the need to simultaneously preserve focusing efficiency and image quality across multiple material states. Here, we present a dynamically tunable metalens based on $Sb_2$$S_3$ operating at the edge of the visible spectrum. The design framework combines finite element computations with a genetic algorithm-based inverse design approach to achieve robust phase control in both amorphous and crystalline states. The resulting metalens shows near-diffraction-limited performance with a focal length tunability of $33\%$, Strehl ratios of $0.80$ and $0.77$ in the amorphous and crystalline states, respectively, and focusing efficiencies of approximately $40\%$ which are among the highest reported for metalenses designed entirely within an active phase-change chalcogenide medium.

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Subrahmanyam S. G. Mantha, Harish N. S. Krishnamoorthy. 2026-06-15. Inverse-designed non-volatile phase change varifocal metalens at the edge of the visible spectrum. https://arxiv.org/abs/2604.00760

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