Metalenses as miniature flat lenses exhibit a substantial potential in replacing traditional optical component. Although the metalenses have been intensively explored, their functions are limited by poor active ability, narrow operating band and small depth of field (DOF). Here, we show a dielectric metalens consisting of TiO2 nanofins array with ultrahigh aspect ratio to realize active multiband varifocal function. Regulating the orbital angular momentum (OAM) by the phase assignment covering the 2π range, its focal lengths can be switched from 5 mm to 35 mm. This active optical multiplexing uses the physical properties of OAM channels to selectively address and decode the vortex beams. The multiband capability and large DOFs with conversion efficiency of 49% for this metalens are validated for both 532 nm and 633 nm, and the incidence wavelength can further change the focal lengths. This non-mechanical tunable metalens demonstrates the possibility of active varifocal metalenses.

For the perfect light absorber, it has been a huge challenge to simultaneously realize ultra‐broadband and strong absorption of unpolarized light over a large angular range, though various materials and designs have been tried. The emergence of optical metasurface with powerful light field regulation ability provides a promising new strategy for achieving perfect absorbers. Here, a Ge2Sb2Te5 (GST)‐based metasurface with an average 92.5%/94.7% (experiment/simulation) absorptivity of unpolarized light, covering an ultra‐broadband from ultraviolet to near‐infrared region is designed and demonstrated. This GST‐based metasurface consists of double‐layer GST interspaced by SiO2 layer, and both field localizations in the top patterned GST layer and intrinsic loss of the bottom patternless GST layer together contribute to this broadband absorption over wide incident angles up to 70°. Strong absorbing ability, large angular responses, and feasibly scalable fabrication for such a perfect GST‐based metasurface absorber offer more promising application opportunities in integrated optoelectronic devices.