  Tunable metasurfaces provide a compact and efficient strategy for optical
components that require active wavefront shaping. Varifocal metalens is one of
the most important applications. However, the existing tunable metalens rarely
serves broadband wavelengths restricting their applications in broadband
imaging and color display due to chromatic aberration. Herein, we demonstrate
an electrically tunable polarization-multiplexed varifocal achromatic
dielectric metalens integrated with twisted nematic liquid crystals (TNLCs) in
the visible region. The phase profiles at different wavelengths under two
orthogonal polarization channels are customized by the particle swarm
optimization algorithm and optimally matched with the metaunits database to
achieve polarization-multiplexed dispersion manipulation including achromatic
performance. By combining the broadband linear polarization conversion ability
of TNLC, the tunability of varifocal achromatic metalens is realized by
applying different voltages. Further, the electrically tunable customized
dispersion-manipulated metalens and switchable color metaholograms are
demonstrated. The proposed devices will accelerate the application of
metasurfaces in broadband zoom imaging, AR/VR displays, and spectral detection.
