Simultaneous Multi-Bit Recording and Driveless Reading for Permanent Storage in Fused Silica

A storage system using fused silica is a promising way to store historically valuable data permanently. To increase recording capacity, we studied the recording and reading conditions for a multilayer sample. The 26-layer sample, which had a recording capacity equivalent to that of a digital versatile disc (DVD), was made with a femtosecond laser and a spatial light modulator (SLM). The recording pulse energy and interlayer crosstalk were reduced by correcting spherical aberration. The sample was evaluated and read with an optical microscope. The signal-to-noise ratio (SNR) criterion of 15 dB was satisfied in all 26 layers by using signal processing. Thermal resistance at 1,000 C for 120 minutes was demonstrated, suggesting a semi-permanent lifetime.