To achieve high bit densities (<10GB/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 30ps) and 400 nm (150 fs). A recording of 72.9 GB/cm3 was achieved, which corresponded to that of 100 compact disks, on aglass plate of (2×2) cm2 and 2.2mm thickness. We also demonstrate separate readouts of three-dimensional memory by (i) transmission imaging using a conventional optical microscope and (ii) photoluminescence (PL) of the bits created by inducing optical damage within the vitreous silica. This shows the potential for two-bit information recording per single bit by means of separate readout procedures.
