Research progress of broadband achromatic infrared metalens (Invited)

Metalenses are two-dimensional metasurfaces composed of sub-wavelength scatters with planar configuration and light focusing function. They can manipulate the amplitude, phase, dispersion and polarization of the light field at sub-wavelength spatial resolution, and develop rapidly in recent years. The subwavelength resonant nanostructure suppresses the high-order diffraction, and the incident light can be perfectly modulated to the predesigned diffraction order, thus ensuring the high efficiency of the metadevice for manipulating the photons. Besides, the design flexibility and specific electromagnetic response of the meta-unit enable metasurfaces to achieve customized control of the multiple dimensions of the light field. In contrast to the traditional refraction lens relying on the phase accumulation effect, the broadband achromatic metalens resolves the complex and bulky limitations of the traditional optical system caused by cascading multiple lenses to correct the chromatic aberration by independently and simultaneously manipulating the phase and phase dispersion of the optical field. It provides a promising way for the miniaturization of on-chip integrated photonics. Focusing on the progress of metalens, this review discussed the basic principles of metasurface on engineering the amplitude, phase and polarization state of the light firstly. Then the development of metalens in recent years was focused on, including the realization of single-wavelength metalens and the development of multi-functional broadband achromatic metalenses through manipulating the multiple parameters (polarization, phase and phase dispersion). Finally, the potential challenges and application prospects for further developing the metalenses were discussed.