We propose and demonstrate a liquid crystal (LC) embedded dielectric metalens with continuously tunable focal length operating at 35 GHz. The lens is composed of a dielectric square hole array filled with a homogenously pre-aligned LC layer. The orientation of LCs can be electrically or magnetically varied, resulting in the dynamic tuning of the transmitted phase of the meta-unit. By elaborately designing the dimension of each meta-unit, the metalens can focus the wave with a variable focal length. We numerically demonstrate a metalens with its focal length tuning from 196.1 to 166.5 mm when the LC orientation gradually varies from 0° to 90°. The transmission of each meta-unit and the full width at half maximum of the focusing intensity are also analyzed, indicating an efficient and satisfactory focusing property. Such a compact and tunable metadevice may facilitate the microwave imaging, communication and so on.
Overcoming chromatic aberrations is a vital concern in imaging systems in order to facilitate full-color and hyperspectral imaging. By contrast, large dispersion holds opportunities for spectroscopy and tomography. Combining both functions into a single component will significantly enhance its versatility. A strategy is proposed to delicately integrate two lenses with a static resonant phase and a switchable geometric phase separately. The former is a metasurface lens with a linear phase dispersion. The latter is composed of liquid crystals (LCs) with space-variant orientations with a phase profile that is frequency independent. By this means, a broadband achromatic focusing from 0.9 to 1.4 THz is revealed. When a saturated bias is applied on LCs, the geometric phase modulation vanishes, leaving only the resonant phase of the metalens. Correspondingly, the device changes from achromatic to dispersive. Furthermore, a metadeflector with tunable dispersion is demonstrated to verify the universality of the proposed method. Our work may pave a way toward active metaoptics, promoting various imaging applications.
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