Three-dimensional optical data storage in vitreous silica

To achieve high bit densities (> 10 GB/cm³) in optical memory, we accomplished a three-dimensional optical data storage system using vitreous silica as the recording material. We succeeded in high-density optical recording by focusing pulsed laser beams of 532 nm (full width at half maximum [FWHM] 30 ps) and 400 nm (150 fs). A recording density of 72.9 GB/cm³ was achieved, which corresponded to that of 100 compact disks, on a glass plate of (2 × 2) cm² and 2.2 mm thickness. We found that the optical damage of silica occurs within 400 ps after irradiation by a single pulse for 30 ps at 532 nm. Three photoluminescence bands were found in the photomodified silica at 283 nm, 468 nm and 558 nm. All the three bands showed similar photoluminescence excitation spectra, i.e. a peak related to oxygen vacancy absorption at 250 nm.