Ultra-wide continuous zoom imaging system based on an Alvarez-Moiré metalens.

Traditional Alvarez lenses realize continuous focal-length adjustment through the relative lateral displacement of two phase plates perpendicular to the optical axis. It will cause the optical aperture of the imaging system based on the traditional Alvarez lenses to become smaller and introduce off-axis aberrations. In this paper, we design and construct an annular-array Alvarez-Moiré metalens continuous zoom imaging system based on moiré rotational focusing. The focal length of the Alvarez-Moiré metalens is tuned through the relative rotation of two cascaded metasurface phase plates. The system mainly consists of a front-end annular array of eight Alvarez-Moiré metalens sub-lenses and a rear cascaded meniscus lens. TiO2 cylindrical nanostructures on a SiO2 substrate are adopted to realize metasurface phase modulation. The front-end metalens module operates at 532 nm, and the overall outer diameter is 14.8 mm. Simulation results show that the proposed system has continuous zoom capability and can realize continuous focal-length adjustment on the order of ±500mm within the relative rotation range. Its continuous zoom imaging capability is verified by the imaging experiment. The results show that clear USAF 1951 resolution target images with continuously changing size can be obtained under different relative rotation angles. The characteristic length varies from 0.78 to 1.61L. The Strehl ratio remains higher than 0.9 over the entire focusing range. These results indicate that the proposed structure maintains good focusing quality during the continuous zoom process and exhibits near-diffraction-limited focusing performance. The proposed system shows potential for compact and integrated continuous zoom imaging devices.