Dynamic Recording of 200 Gbytes in Three-Dimensional Optical Disk by a 405 nm Wavelength Picosecond Laser

We present experimental results of our volumetric optical data storage system. To achieve volumetric recording over a wide depth range of 250 μm in a recording medium, we developed a relay lens system for compensating for the spherical aberration of a high-numerical-aperture (0.85) objective lens. T...

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Published inJapanese Journal of Applied Physics Vol. 50; no. 3; pp. 032704 - 032704-7
Main Authors Ueda, Daisuke, Saito, Kimihiro, Iwamura, Takashi, Takemoto, Yoshihiro, Yamatsu, Hisayuki, Horigome, Toshihiro, Oyamada, Mitsuaki, Hayashi, Kunihiko, Tanabe, Norihiro, Miyamoto, Hirotaka, Nakaoki, Ariyoshi, Horigome, Junichi, Uchiyama, Hiroshi, Yun, KyungSung, Kobayashi, Seiji
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.03.2011
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Summary:We present experimental results of our volumetric optical data storage system. To achieve volumetric recording over a wide depth range of 250 μm in a recording medium, we developed a relay lens system for compensating for the spherical aberration of a high-numerical-aperture (0.85) objective lens. The disk employs a single monolithic recording layer and a reference layer for servo control. A 405-nm-wavelength titanium:sapphire laser that exhibits 2 ps pulse duration and a more than 2 kW peak power is used for recording. We adopted void formation and mark position as recording principles. We have experimentally demonstrated 34-layer dynamic recording, corresponding to a capacity of 200 Gbytes.
Bibliography:Schematic images of two types media structure. On the basis of a scalar diffraction model, we performed simulations. We took into account only two layers (L0 and L1). The ellipsoid shape of void marks are represented by 20 microlayers. We assumed a track pitch of 0.64 μm and a minimum mark-to-mark distance of 465 nm. Cross-sectional image of a typical void mark. From this image we recognize that the horizontal diameter is 180 nm and the vertical diameter is 260 nm. Simulated eye pattern of VFM mark-position signal. We observe a good-quality eye pattern even at an interlayer distance ($dz$) of 8 μm. According to the simulation, we calculated the jitter value as a function of interlayer distance $dz$. We observe less than 6% jitter values when $dz$ is over 6 μm. Schematic diagram of our experimental setup. We use 3 different lasers: a Ti:Sa picosecond laser, which exhibits pulses of 2 ps and the maximum peak-power of 2 kW, a conventional blue laser diode (shown as BLD) for readout, and a 660 nm red laser diode for servo system. The Ti:Sa laser is modulated by an electrooptic modulator (EOM). Our medium structure. The recording layer is monolithic, made of an organic material of 250 μm thickness. We apply a reference layer of 50 μm thickness to obtain tracking and focusing servo signals. After recording 18 layers with a layer spacing of 10 μm, we observed the cross section of the disk using FIB-SEM. In this figure, we show parts of 18 layer images. (The depths of 238, 228, ${\ldots}$, 68 μm.) From these images, we confirm that small (approximately 300 nm in diameter) void marks are formed deep inside of the medium. We show CNR as a function of recording peak power at various mark-to-mark distances, $p$. Eye patterns of the 34-layer data recording. We recorded 10 tracks for each layer. These signals are obtained immediately after the recording. No signal equalizer is applied. The distance between consecutive layers is 6.8 μm. In this figure, the distance from the surface of the disk is indicated at the top of each playback signal. We observe that the expected signal waveform of VFM modulation is obtained from all of 34 layers. From the playback signal acquired right after recording to the layer, we measured the jitter values and bER. We observe good jitter values and good bERs. After all the 34 layers are recorded, we replaced our focal position to the recorded layers. 9 layers (i.e., Layer 3, 5, 10, 14, 17, 19, 25, 30, and 34) are found and the jitter value and bER obtained from those layers are plotted in this figure. These values show degradation caused by the layers recorded above.
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.50.032704