Mechanically reconfigurable layered GRIN lenses for mid-infrared

Abstract

This paper presents a concept of mechanically adjustable planar Gradientindex (GRIN) lens that can be used to realize reconfigurable focusing at mid-infrared (mid-IR) or millimeter-wave (mm-wave) frequencies. The concept is based on a multilayer design rooted in effective medium theory, where spatial refractive index profiles are synthesized using first-kind Chebyshev polynomials. Symmetric lateral displacement of the layers enables continuous modulation of the effective refractive index distribution, allowing controlled transitions between divergent, afocal, and convergent wavefronts. Numerical simulations demonstrate accurate focal tuning at mid-IR and mm-waves. In the mid-IR regime, focal lengths of about 56 μm and 24 μm are achieved with relative errors of around 4.4% and 10%, respectively. In the mm-wave regime, the lens produces focal lengths of about 158 mm and 128 mm with improved accuracies of 2.3% and 6.0%, respectively. The reconstructed refractive index profiles exhibit high similarity to ideal convex lens distributions, confirming the validity of the proposed synthesis approach. The proposed GRIN lens concept offers a scalable and physically interpretable approach to reconfigurable focusing, with potential applications in multimodal imaging, adaptive sensing, and telecommunication systems.