A Driveless Read System for Permanently Recorded Data in Fused Silica

Abstract

A driveless, multilayer read system was demonstrated as applicable to a permanent digital-storage using fused silica. The combination of a low-magnification microscope and signal processing were simple enough to be emulated in the distant future. Test data were recorded in a 2-mm-thick fused-silica plate by a femtosecond laser to form four layers with dot pitch of 2.8 µm and interlayer distance of 60 µm. The total recording density was 40 Mbytes/in.2, which is as high as that of a conventional compact disc. This system achieved a bit-error rate in the order of 10-3 when reading the test data (without error-correction code) from images taken at a 19.5-times-magnification. Signal processing using unsharp masking and subtraction of images at different focal points effectively contribute to read data from blurred image with the low bit-error rate.

Permanent data recording in transparent materials by using a nanojoule-class pulse laser

“…The line in the figure shows the contrast of dots recorded in silica glass by the regenerative amplified laser used in our previous work. 14,15) The contrast of dots recorded in both silica glass and Lumicera Ò is higher than that of the dots recorded in silica glass by an amplified laser. This means that Lumicera Ò has a higher sensitivity to the recording laser light than silica glass.…”

“…14) A technology for enabling simple access to the digital data by using a conventional optical microscope was also developed. 15) Two issues concerning the previous storage system, however, remain to be overcome. The first issue is low recording speed.…”

“…14,15) The pulse energy necessary for the structural modification of a recording medium should be low compared with that of the previous medium, since the pulse energy of a femtosecond laser without amplification is several tens of nanojoules, namely, about 10 5 times lower than that of amplified light. In addition, the signal intensity of the modified area should be high enough to read data using commercially available cameras, whose optical performances are low compared with that of an optical microscope.…”

Progress in ultrafast laser processing and future prospects

“…Binary information based on digital bits has been successfully recorded by writing nanovoids in multiple planes with a density of 17 Gbits/cm 3 [8]. It has recently been demonstrated that the digital bits inscribed in fused silica with a femtosecond laser have a long-term data storage lifetime of more than 319 million years, which has been confirmed by the accelerated test at 1000°C for 120 min [94]. The recording density written by holographic femtosecond laser processing using a spatial light modulator (SLM) reached 40 Mbyte/inch 2 with a dot pitch of 2.8 µm in four layers, which is greater than that of a compact disk.…”

Femtosecond laser three-dimensional micro- and nanofabrication

“…Recording digital bits in fused silica with femtosecond laser induced multiphoton absorption has been recognized as a potential solution, because fused silica is a material with excellent thermal and chemical stability. [156][157][158][159] In addition, the 3D capability of this approach holds the promise of achieving ultrahigh-density data storage.…”