Stretchable Achromatic Metalens with Ultra-wide Focal Tunability for Near-Infrared Adaptive Optics

This study addresses the inherent limitations of conventional metalenses, specifically their rigid substrates and static focal lengths, which constrain their utility in dynamic and conformal optical systems. We present the development of a flexible, achromatic metalens engineered for operation within the near-infrared (NIR) spectrum (870–1080 nm). This innovative design incorporates a stretchable polydimethylsiloxane substrate embedded with a Silicon-MgF₂ cross-square nanoblock. The resultant metalens exhibits exceptional focal length tunability, achieving a remarkable 206% variation through mechanical stretching ranging from 0% to 30%. Crucially, it sustains polarization-insensitive focusing with stable efficiencies ranging from 50% to 64% across bandwidth and stretching ratios. Through the integration of an anti-reflective material, the application of nanostructure property optimization techniques, and the utilization of a hybrid cross-square nanoblocks, the metalens demonstrates minimal chromatic aberration and maintains stable focusing efficiency despite mechanical deformation. Finite-difference time-domain (FDTD) simulations rigorously validate its diffraction-limited performance across all states. This advancement has significant implications for adaptive optics in biomedical imaging, telecommunications, and augmented reality, thereby facilitating the development of versatile, high-performance photonic devices for flexible and wearable technologies.