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Reconfigurable All-Dielectric Metalens with Diffraction-Limited Performance

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Journal Article - Open Access

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MIT Lincoln Laboratory Lexington United States

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Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning covering the full 2n range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials O-PCMs. We present a generic design principle enabling switching of metasurfaces between two arbitrary phase profiles and propose a new figure-of-merit FOM tailored for active meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 um wavelength. The metalens is constructed using Ge2Sb2Se4Te1 GSST, an O-PCM with a large refractive index contrast An 1 and unique broadband low-loss characteristics in both amorphous and crystalline states. The reconfigurable metalens features focusing efficiencies above 20 at both states for linearly polarized light and a record large switching contrast ratio of 29.5 dB. We further validated aberration-free imaging using the metalens at both optical states, which represents the first experimental demonstration of a non-mechanical active metalens with diffraction-limited performance.

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