Metalens, one of the most prominent applications of metasurface, has demonstrated promising abilities to replace traditional lens. By manipulating the phase distribution of metalens composed of appropriately arranged meta-atoms, the wavefront of incidence can be arbitrarily controlled to achieve desired purposes.
Broadband achromatic metalens (BAM) correcting chromatic aberration in broadband applications has gradually consolidated its position in the past few years. However, the proposed BAMs were limited to single functionality which impedes potential applications after fabrication. The continuously varifocal metalens for broadband achromatic focusing is still a challenge.
To overcome this challenge, a research team led by Prof. Dr. FAN Wenhui from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) proposed a metalens for designing tunable BAMs, which is called continuously varifocal and broadband achromatic metalens (CVBAM). The study was published in Journal of Science: Advanced Materials and Devices. The researchers selected semiconductor material of indium antimonide (InSb) with tunable responses to design meta-atoms for accomplishing phase compensation required by CVBAM that has the operation frequency range of 1.8 - 2.2 THz.
The CVBAM was designed to converge the focal spots to preset spatial location over the operation frequency range. By varying external temperature, the focal length of CVBAM can be dynamically tunned from 736.25 μm to 861.02 μm, while the achromatic focusing can be maintained as well.
The proposed metalens can significantly enrich the capabilities and potential applications of current meta-devices, which may facilitate the development of THz near-field imaging and spectroscopy systems.
