Direct-Readout Optical Archival Storage in Fused Silica Using QR Microstructures

Developing practical long-term optical archival storage technologies remains a significant challenge. Although high-density femtosecond-laser-based optical storage in fused silica offers exceptional durability, advanced volumetric approaches often require specialized readout systems, limiting practical deployment. Here, we propose a direct-readout optical storage framework based on surface-relief microstructures, combining two-photon lithography (TPL), reactive ion etching (RIE), and conventional microscopic imaging. Raw data are first encoded into QR codes and subsequently converted into three-dimensional QR microstructures for fabrication. A scan-line QR writing strategy is proposed, reducing the TPL writing time by approximately 80%. The fabricated QR microstructures are permanently transferred into fused silica by RIE and can be directly read using a conventional optical microscope. A hierarchy-aware QR reconstruction algorithm is further developed to recover complete QR codes from contour-dominated microscopic images. The proposed framework has an estimated geometric storage capacity of 2.85 GB per disc and a fabrication success rate of 94.5%, demonstrating a practical and highly accessible approach for long-term optical archival storage.