Metalenses based on optical metasurfaces enable wavefront manipulation using subwavelength nanostructures and provide a promising route toward compact and integrated optical systems. However, strong chromatic aberration caused by wavelength-dependent phase responses remains a major obstacle for practical metalens applications in the visible regime.

In this work, we present the design and analysis of an achromatic metalens operating in the visible spectrum using silicon nitride (Si₃N₄) dielectric metasurfaces. The metalens employs a phase-engineering strategy based on propagation-phase modulation of polarization-independent nanostructures. By constructing a unit-cell phase library through systematic parameter scanning, the phase responses at different wavelengths are accurately mapped. An interleaved arrangement strategy is introduced, where meta-atoms designed for different target wavelengths are alternately distributed within a single metalens aperture, enabling multi-wavelength phase compensation without increasing structural complexity.

Numerical simulations demonstrate that the proposed metalens achieves near-coincident focal positions across a broad visible wavelength range. The focal length variation is significantly suppressed compared with conventional single-wavelength metalenses. The metalens exhibits stable focusing behavior with symmetric focal spots, consistent focal sizes, and improved chromatic tolerance. The results confirm that the interleaved design effectively mitigates chromatic focal shift while maintaining high transmission efficiency.

This study provides a practical and scalable approach to achieving achromatic focusing in visible-wavelength metalenses. The proposed Si₃N₄-based interleaved design offers strong potential for compact imaging systems, integrated photonics, and visible-light optical devices.