Versatile Disk-random Access Memory Research Articles

Analysis of behavior of focusing error signals generated by astigmatic method when a focused spot moves beyond the radius of a land-groove-type optical disk

We theoretically calculate behaviors of focusing error signals generated by an astigmatic method in a land-groove-type optical disk. The focusing error signal from the land does not coincide with that from the groove. This behavior is enhanced when a focused spot of an optical pickup moves beyond the radius of the optical disk. A gain difference between the slope sensitivities of focusing error signals from the land and the groove is an important factor with respect to stable focusing servo control. In our calculation, the format of digital versatile disc-random access memory (DVD-RAM) is adopted as the land-groove-type optical disk model, and the dependences of the gain difference on various factors are investigated. The gain difference strongly depends on the optical intensity distribution of the laser beam in the optical pickup. The calculation method and results in this paper will be reflected in newly developed land-groove-type optical disks.

Analysis of focusing error signals by differential astigmatic method under off-center tracking in the land-groove-type optical disk

We theoretically calculate the behavior of the focusing error signal in the land-groove-type optical disk when the objective lens traverses on out of the radius of the optical disk. The differential astigmatic method is employed instead of the conventional astigmatic method for generating the focusing error signals. The signal behaviors are compared and analyzed in terms of the gain difference of the slope sensitivity of the focusing error signals from the land and the groove. In our calculation, the format of digital versatile disc-random access memory (DVD-RAM) is adopted as the land-groove-type optical disk model, and advantageous conditions for suppressing the gain difference are investigated. The calculation method and results described in this paper will be reflected in the next generation land-groove-type optical disks.

Analysis of Behavior of Focusing Error Signals in Astigmatic Method in the Scheme of Land–Groove Recording

We present the behavior of focusing error signals in a land-groove-type optical disk by theoretical analysis. A gain difference between focusing error signals from a land and a groove occurs because the focusing error signal from the land does not coincide with that from the groove. We also report the dependence of the gain difference on some factors, which are related to the intensity distribution of a laser beam. The physical format of digital versatile disk random access memory is used as a land-groove-type optical disk model. The simulation results show that coma aberration that distorts the intensity distribution unidirectionally causes a large gain difference.

In-Line-Type Differential Push-Pull Methods for Tracking Error Detection

The validity of in-line-type differential push-pull (DPP) methods for digital versatile disc-recordable (DVD-R) and digital versatile disc-random access memory (DVD-RAM) is presented by numerical calculation. In these methods, segmented gratings which are divided into two or three regions each with a specific phase value and a width are used to generate subspots on the optical disk. Tracking error signals are calculated with respect to the objective lens shift under parameter conditions of the widths of the segmented regions. The obtained results show that the relationship between the signal characteristics and grating types becomes clear in both cases of DVD-R and DVD-RAM.

Existence of tetrahedral site symmetry about Ge atoms in a single-crystal film of Ge2Sb2Te5 found by x-ray fluorescence holography

The authors discuss x-ray fluorescence holography (XFH) measurements taken from an epitaxial layer of the digital versatile disk random access memory (DVD-RAM) material Ge2Sb2Te5 grown on a single-crystal GaSb(100) substrate. By using fluorescent photons from the Ge atoms in the matrix, a three-dimensional atomic image was obtained around the Ge atoms in a Ge2Sb2Te5 film; details of the three-dimensional atomic arrangement will aim at clarification of the high-speed writing and erasing mechanism of the laser-induced crystal-amorphous phase transition in this DVD-RAM material. Analysis of the XFH images revealed that the epitaxial layer did not possess a hexagonal structure as in the equilibrium phase of Ge2Sb2Te5, but a cubic structure with tetrahedral site symmetry about Ge atoms, different from the previous powder diffraction result. The present structure may support the umbrella-flip model of the Ge atoms between the octahedral site in the distorted rocksalt crystal and the tetrahedral site in the amorphous phase on the laser-induced phase transition.

Enhancement of Speed Margins for 16× Digital Versatile Disc-Random Access Memory

We have evaluated the speed margins of write/read 16× digital versatile disc-random access memory (DVD-RAM) test discs using write strategies for 6–16× constant angular velocity (CAV) control. Our approach is to determine the writing parameters for the middle zones by interpolating the zone numbers. Using this interpolation strategy, we successfully obtained overwrite jitter values of less than 8% and bit error rates of less than 10-5 in 6–16× DVD-RAM. Moreover, we confirmed that the speed margins were ±20% for a 6–16× CAV.

Physical Characteristics and Format of a Two-Inch-Diameter Magneto-Optical Disk System with 3 GB Capacity

Recording at a high density four times that of a current digital versatile disk random access memory (DVD-RAM) has been achieved by applying the domain wall displacement detection (DWDD) technology using a conventional optical head with the same wavelength of 660 nm and numerical aperture (NA) of 0.60 as those the DVD head. It has been confirmed by using an alternating sampled servo, laser annealing of the inter track area and partial response maximum likelihood (PRML) that a recording density of 15 Gbit/inch2 with a track pitch of 540 nm and bit length of 80 nm has sufficient system margins. A newly developed 1-bit-distributed address format has achieved a redundancy of 23%. Furthermore, the edge shift compensation technique has reduced the recording magnetic field. These indicate that a capacity of 3 GB on a two-inch-diameter disk is now available for mobile use. If applied to a digital video camera, one hour or more of moving-picture-experts-group-2 (MPEG2) video contents can be recorded at a bit rate of 6 Mbps.

Observation of recording pits on phase-change film using a scanning probe microscope

A phase-change film is a key material for optical data storage media such as rewritable compact disks (CD-RW) and digital versatile disk random access memory (CD-RAM). Data pits are recorded as differences in crystal state (crystallized state vs. amorphous state) on phase-change film. It is very important to distinguish the crystal state difference in a very small area for material research of phase-change film. Measuring size and shape of recorded data pits is also very important for the development to achieve good data reliability and high data density of optical data storage media. The crystal state difference in very small areas of phase-change film is successfully observed by Kelvin probe force microscopy (KFM) and scanning near-field optical/atomic force microscopy (SNOAM). The advantage of KFM and SNOAM for measuring physical property differences in a very small area is demonstrated.

New Method of Calibrating Adaptive Writing Pulses for Digital Versatile Disc Random Access Memory (DVD-RAM) 4.7 GB Drive

In this paper, a new method of calibrating adaptive writing pulses suitable for installing into the digital versatile disc random access memory (DVD-RAM) 4.7 GB drive is described. To obtain a wider margin of write/read operation, it is desirable to optimize all adaptive parameters for every disk inserted into the drive. We propose the jitter minimizing (JM) method, which is characterized by using selected test patterns, detecting only jitter in the drive and applying a search algorithm to obtain bottom jitter. As a result of optimizing all parameters by JM, the total calibration time is 4.8 s with the accuracy of ≤1 ns, and overwrite jitter of random data is 8.6% at the drive. It is proved that JM offers the same results as the measurement by the time interval analyzer (TIA), uses small-sized hardware and exhibits satisfactory performance for application in commercial drives.

High-Resolution Examination of Recording Marks in Phase-Change Media Using a Scanning Near-Field Optical Microscope

Recording marks in digital versatile disc-random access memory (DVD-RAM) were examined using a scanning near-field optical microscope (SNOM) incorporating an improved probe tip design. The marks were recorded on an experimental DVD-RAM medium with a track-pitch of 0.6 µm. The tip size of the SNOM was made wider than the track width in order to avoid optical ghosting arising from the track edge. The recording power was varied in order to investigate the dependence of the mark shape on power and it was found that the mark shape correlated well with the reproduced signal. The SNOM is considered to be a good candidate for a practical characterization tool for optical recording media.