Aperture-shared metalens for generating frequency- and polarization-multiplexed terahertz holograms

In this paper, we propose a method to reconstruct frequency- and polarization-multiplexed terahertz (THz) holograms using an aperture-shared metalens composed of merely a single type of meta-atom structure. The focal points generated by the multi-foci metalens serve as the pixels of the holographic images. The designed meta-atom exhibits high circular polarization conversion efficiency at three frequencies; thus, the design of geometric phase metasurfaces can be implemented simultaneously at these three frequencies. A multi-foci metalens is designed using a phase multiplexing approach, with frequency multiplexing achieved through a shared aperture. Meanwhile, during the phase multiplexing design process, the edge phase profiles of different frequencies are adjusted to ensure that the focal spot sizes corresponding to different frequencies remain identical. Two design frequencies are selected for the reconstruction of final frequency-multiplexed holograms after accounting for the influence of dispersion. Additionally, amplitude coefficients are introduced into the phase profile design to mitigate the dispersive effects between different frequencies. Ultimately, through the simultaneous multiplexing of frequency and polarization, the reconstruction of holographic images with nearly uniform intensities across different frequencies is achieved after polarization detection. Our design method enables a single metasurface to simultaneously carry multiple images or pieces of information, which can enhance information density and, thus, holds application potential in fields such as THz communication, information storage, and encryption.