Coded cholesteric LC metalens for broadband achromatic imaging

Liquid crystals (LC) planar optical elements have attracted much interests owning to its simple fabrication and powerful beam shaping capability. Among them, cholesteric liquid crystals (CLC) have received widespread attention due to their self-assembly behavior, natural chiral structure, circular polarization selectivity, and Pancharatnam–Berry (PB) phase modulation capability. However, traditional CLC lenses suffer from significant chromatic aberration which results in single wavelength or narrow bandwidth imaging only. Conventional way to solve the chromatic aberration is either combining LC lens with a refractive lens with opposite dispersion or designing multiple layers for a few discrete wavelengths, resulting in the optical system bulky and complicated. Here, we propose and demonstrate a single-chip achromatic CLC lens for broad and continuous wavelength band imaging. The proposed CLC lens utilizes cubic wavefront encoding technology and is prepared using optical orientation technology, avoiding the complex manufacturing process of conventional metalenses. Experimental results demonstrate that an F/#30 lens with a coding parameter of 20 can achieve achromatic imaging with a total bandwidth of 80 nm across the entire Bragg reflection band. This study opens an avenue for the achromatic manipulation of CLC lenses and has great potential in the field of imaging, display and dispersion management.