Differentiable library-based inverse design of achromatic metalens for full-color near-eye displays

Achromatic metalenses capable of full-color imaging are essential for compact near-eye displays, yet their practical realization remains challenging by trade-offs among wavelength multiplexing, focusing efficiency, fabrication complexity, and scalability. We address these challenges with a fabrication-constrained inverse design framework that uses a discrete 3D meta-atom library. Each radial pixel selects a manufacturable cylinder from the library using a Gumbel-Softmax estimator, enabling gradient updates. We optimize focusing efficiency, maximizing it while maintaining uniform efficiency across RGB wavelengths. Leveraging two-photon lithography to independently control pillar height and diameter, the designed 3D RGB achromatic metalens achieves ~33% focusing efficiency at the design wavelengths using low-index structures. To improve scalability, a conformal SiO₂ atomic protection layer deposited by low-damage plasma-enhanced atomic layer deposition enables reliable nanoimprint lithography while preserving structural fidelity. The resulting metalenses exhibit diffraction-limited performance and are integrated with an OLED panel to demonstrate a compact, full-color near-eye virtual reality system without chromatic aberration.