Uniform Thermo-Optic Tunability of Dielectric Metalenses

The field of low-loss dielectric metasurfaces has created a new paradigm of miniaturization for free-space optical elements. We study the effects of uniformly changing the refractive index of high-index metalenses. We experimentally demonstrate a modal refractive-index change (ΔnMD=0.15) in the fundamental Mie resonances in an InSb resonator based on traditional thermo-optic effects. We develop a high aspect ratio metasurface design with simulated 75-90% transmission efficiency and 2π phase shift as a function of cylinder radius. A metalens is shown to have high (>60%) focusing efficiencies for large (up to 0.8) numerical aperture designs. The uniform thermal tuning of the metalens system is studied based on the variations in the spatial phase profile of the individual resonators. We demonstrate that both the operating wavelength (Δλf=500nm) and the focal length (Δf = 45 μm) can be dynamically modified based on the chromatic dispersion of the engineered metalens. The results show that static metasurfaces made of high-index semiconductors can be thermally actuated to tune the operating focal wavelength and focal length.