A titanium oxide (TiO2) metasurface is emerging as a promising platform for arbitrary control of visible light and has been demonstrated for metalenses, a helicity multiplexed hologram, chiral spectroscopy, and structural colors. Among these, the generated orbital angular momentum (OAM) beam endows additional freedom in complex light–matter interactions. Manipulating multiple OAM channels within a single metadevice is highly coveted, and such capability proves advantageous for the advancement of integrated photonic chips and the creation of miniaturized optical systems tailored for applications involving OAM light. Here, an all-dielectric metasurface made of spatially rotated TiO2 nanofins is demonstrated experimentally for the generation, spatial multiplexing, and focusing of the OAM light in both angular and distance domains. In particular, our metadevice could reconstruct four different topologically charged beams into four different directions and focus in four different planes in a broadband manner. The ultracompact spatially multiplexing on-chip metadevice may inspire exterior photonic applications with versatile integrated functionalities.
Zhu et al. (Mon,) studied this question.