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Metasurface optics provide an ultra-thin alternative to conventional refractive lenses. A present challenge is in realizing metasurfaces that exhibit tunable optical properties and achromatic behavior across the visible spectrum. Here, we report the design, fabrication, and characterization of metasurface lenses (metalenses) that use asymmetric TiO2 nanostructures to induce a polarization-dependent optical response. By rotating the polarization of linearly-polarized input light, the focal length of a 40 micrometer-diameter metalens is tuned from 220-550 micrometers with nearly diffraction-limited performance. We show that imparting a wavelength-dependent polarization rotation on incident light enables achromatic focusing over a wide band of the visible spectrum, 483-620 nm. We use this property to demonstrate varifocal color imaging with white light from a halogen source. Tunable achromatic metalenses may be useful for applications in imaging and display.
Optical metasurfaces have shown to be a powerful approach to planar optical elements, enabling an unprecedented control over light phase and amplitude. At that stage, where wide variety of static functionalities have been accomplished, most efforts a
Recently, an achromatic metasurface was successfully demonstrated to deflect light of multiple wavelengths in the same direction and it was further applied to the design of planar lenses without chromatic aberrations [Science, 347, 1342(2015)]. Howev
Vanadium dioxide (VO2) is a model system that has been used to understand closely-occurring multiband electronic (Mott) and structural (Peierls) transitions for over half a century due to continued scientific and technological interests. Among the ma
To efficiently integrate cutting-edge terahertz technology into compact devices, the highly confined terahertz plasmons are attracting intensive attentions. Compared to plasmons at visible frequencies in metals, terahertz plasmons, typically in light
Local, bulk response functions, e.g permittivity, and the macroscopic Maxwell equations completely specify the classical electromagnetic problem, which features only wavelength $lambda$ and geometric scales. The above neglect of intrinsic electronic