Design of meta-surface lens integrated with pupil filter

<sec>Metasurface lenses are miniature flat lenses that can precisely control the phase, amplitude, and polarization of incident light by modulating the parameters of each unit on the substrate. Compared with conventional optical lenses, they have the advantages of small size, light weight, and high integration, and are the core components of photonic chips. Currently, the hot topics for metasurface lens are broadband and achromatic devices, and there is still less attention paid to the resolution improvement. To break through the diffraction limit and further improve the focusing performance and imaging resolution of metasurface lenses, we use unit cells to perform multi-dimensional modulation of the incident light field. Specifically, in this paper, we combine phase modulation of metasurface lens with a pupil filtering, which has been widely applied to traditional microscopy imaging and adaptive optics and has demonstrated powerful resolution enhancement effects. The integrating of these two technologies will continue to improve the imaging performance of metasurface lenses and thus expanding their application fields.</sec><sec>In this work, we firstly design a single-cell super-surface lens composed of a silicon nanofin array and a silica substrate as a benchmark for comparing the performance of integrated super-surface lens. The lens achieves an ideal focal spot for incident light at 633 nm, resulting in a full width at half maximum (FWHM) of 376.0 nm. Then, a three-zone phase modulating pupil filter is proposed and designed with the same aperture of metasurface lens, which has a phase jump of 0-π-0 from the inside to the outside of the aperture. From the simulation results, the main lobe size of the focal spot is compressed obviously. In the optimization, its structural parameters are scanned for the best performance, and an optimal set of structural parameters is selected and used in the integrated metasurface lens. Finally, the integrated metasurface lens is designed by combining the metasurface lens with a three-zone phase modulating pupil filter, and the FWHM of its focal spot is compressed to 323.4 nm (≈ 0.51<i>λ</i>), which is not only 15% smaller than original metasurface lens’s FWHM of 376.0 nm, but also much smaller than the diffraction limit of 0.61<i>λ</i>/<i>NA</i> (when <i>NA</i> = 0.9, it is approximately 429.0 nm). This result preliminarily demonstrates the super-resolution performance of the integrated super-surface lens. With the comprehensive regulation of multi-dimensional information, such as amplitude, polarization, and vortex, the integrated super-surface optical lens will achieve more excellent super-resolution focusing and imaging performance, and will also be widely used in the fields of super-resolution imaging, virtual reality, and three-dimensional optical display, due to its characteristics of high resolution, high integration, and high miniaturization.</sec>