Varifocal metalens based optical sectioning fluorescence imaging system

Based on the Moiré effect, a pairwise ultrathin flat Moiré metalens is designed and fabricated. The diameter of the metalens is 1.6 mm. According to the mutual angles between two metasurfaces, the focal length tuning range of Moiré metalens is ∼115 mm with ∼40 % transmission efficiency at 532 nm. In addition, the Moiré metalens is implemented to a telecentric design to form the long axial scanning range imaging system with constant magnification. The scanning range of the telecentric imaging system is around 75 μm. The long tuning range with constant magnification is demonstrated by the imaging resolution chart that shows the lateral resolution of the system is around 2 μm. The proposed telecentric imaging system combines with structure illumination-based HiLo imaging principle to obtain the fine optical sectioning fluorescence images with invariant image contrast in the scanning range. The experiment results of the fluorescence beads show the optical sectioning capability of the system is around 7 μm. The ex-vivo fluorescence image results of the mice intestine tissue indicate that the system has the ability to obtain three different depths sectioning images. With the help of the HiLo imaging process, the defocus background noise can be suppressed, and the in focus villi detailed structure can be captured with high signal-to-noise ratio. The proposed varifocal ultrathin size of Moiré metalens has great potentials to replace the conventional bulky varifocal lens for compact system design of optical systems.