Octave bandwidth aperiodic achromatic metalens in the infrared

With the rapid development of portable equipment, the demand for the miniaturization of optical elements is increasing. Metasurfaces are considered as potential planar analogs of conventional devices due to their small size and their extraordinary ability to modulate light. As one of the most important branches of metasurfaces, metalenses attract much attention and are fascinating to develop compact, miniature optical imaging devices. However, the highly chromatic characteristic limits their further applications. Therefore, achromatic metalenses with constant focal lengths over a broad bandwidth are highly desirable. Here, we demonstrate a diffraction-limited achromatic metalens with an octave-wide bandwidth in the infrared. Unlike typical metalenses with periodic unit cells, the proposed metalens compriseswell-designed an aperiodic array of elements based on the Pancharatnam-Berry phase. The proposed metalenswith a numerical aperture of 0.49 achieves an average focusing efficiency of 37% in a wavelength range from 1.15 to 2.3 mu m, which is one octave, andmaintains a near-constant focal length of 25 mu m. It paves the way forminiaturized and broadband imaging applications.