Metasurface lenses are miniature flat lenses that achieve precise control of 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 little 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 for the first time, which has been widely applied in traditional microscopy imaging and adaptive optics, and has demonstrated powerful resolution enhancement effects. The fusion of these two technologies will continue to improve the imaging performance of metasurface lenses and expand their application fields.
In this article, 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 fused super-surface lens. The lens achieves an ideal focal spot for incident light at 633 nm, resulting in a FWHM of 376.0 nm. Then, a three-zone phase modulating pupil filter was proposed and designed with the same aperture of metasurface lens, which has a phase jump of 0-π-0 from inside to outside of the aperture. From the simulation results, the main lobe size of the focal spot has been compressed obviously. In the optimization, its structural parameters were scanned for the best performance, and the optimal set of structural parameters was selected and applied in the fusion metasurface lens. Finally, the fused metasurface lens was designed by combining the metasurface lens with the three-zone phase modulating pupil filter, and the FWHM of its focal spot was compressed to 323.4 nm (≈0.51λ), 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 0.61λ/NA (when NA=0.9, it is approximately 429.0 nm). This result preliminarily demonstrates the super-resolution performance of the fused super-surface lens. With the comprehensive regulation of multi-dimensional information, such as amplitude, polarization, and vortex, the fused 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 3-D optical display, due to its characteristics of high resolution, high integration, and high miniaturization.