A new MSR method is proposed for a high density magneto-optical (MO) recording. It is based on the reorientation of the readout layer magnetization near its compensation temperature. The range of temperature within the readout process occurs depends strongly on both physical properties of memory and readout layer and also dynamic parameters such as medium velocity and laser characteristics. The adequate choice of the readout layer composition and thickness is a main key to control the exchange coupling between the two layers and therefore optimizing the readout resolution of the MSR technique.

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Stable domain structure in a readout layer with a small perpendicular anisotropy has been analyzed by comparing energies for three models.

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Simulation of the wall motion in Domain Wall Displacement Detection media has been carried out for the two kinds of the displacement layers. It has been found that the wall motion in the displacement layer with the reduced exchange energy has to be treated as the physical phenomenon which is different from that in the ordinary displacement layer. The improvement of the wall motion in the displacement layer with the reduced exchange energy depends on the clever control of the stray field.

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We have equipped a commercial polarized-light microscope with two laser diodes operating at 643 nm and 680 nm. The two laser beams are focused simultaneously and coincidentally on the sample through the microscope objective lens. We use one of the lasers in the pulsed mode to write marks on the sample, and the other laser in a low-power cw mode to monitor the changes in reflectivity and/or the state of polarization upon reflection from the sample. The system has a liquid crystal wave-plate for adjusting the optical phase-shifts, an electro-magnet, a hot plate, a computerized XY-stage, two polarizing beam-splitters, and both single-ended and differential detection modules for each of the laser wavelengths.
The dynamics of phase-transition (i.e., melting, crystallization, and amorphization upon rapid cooling from melt in the case of PC media, and ferrimagnetic-to-paramagnetic in the case of MO media) are readily observed in the 160 MHz-bandwidth signal picked up by the detectors. Similarly, changes in the magnetic state of the MO media under a focused spot (whether due to the change of temperature or caused by magnetization reversal), are monitored in real-time.
We describe the dynamics of phase transformation in PC media as well as the observed behavior of magnetization of the MO media within the region of the hot spot. These observations are made over periods ranging from 30 ns up to several microseconds, with a resolution of only a few nanoseconds. We also outline the methods of extracting from the observed data the physical parameters of the media such as the specific heat, thermal conductivity, temperature-dependence of the optical constants, and the probabilities of nucleation and growth.

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An integrated design software to analyze optical, thermal and crystallization characteristics of phase change optical disks has been developed. It has been applied to simulate the reflectivity of nano-scale thin films, mark size, effect of super-RENS and effects of sulfur atom diffusion on the recording performance. In order to verify the simulation results, a set of experiments has been designed and carried out. The study results show that the software can simulate accurately the practical processes and then obtain reliable results. The software has been applied to design DVD-RAM 4.7 GB disks with multi layer structure. Based on these simulation results, 4.7 GB/side DVD-RAM disks that can fully meet the DVD-RAM standard have been successfully fabricated, which shows that the software is a powerful tool for the phase change optical disk design.

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Future development of erasable phase-change recording requires an understanding of amorphization and crystallization mechanisms. Thermodynamical models allow to describe the phase transformation occurring under a given heat treatment. However, a key point for a suitable application of thermodynamical models to phase change recording media is to take into account temperature variations generated during laser heating. In this paper, the temperature profiles are evaluated on the basis of optical and thermal simulations and re-introduced in the thermodynamical models. The experimental study of laser induced phase transformations including both optical measurements and microstructure analysis allows to discuss the validity of the models.

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We describe the results of the simulation and the examination and the basic physical characteristics of DVD-RW disc adopting two-depth substrate to deal with read only data on the rewritable material. This feature is required to make the copyright protection and management possible at the same time. Moreover, it will be able to realize the higher compatibility with legacy DVD-players and drives already in the market.

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A new method of eliminating the initializing process from phase change recording media production has been proposed. The process is based on the use of krypton instead of argon for the deposition of GeSbTe recording film. By this method the kinetic energy of sputtered atoms can be reduced by collisions with gas atoms. Fairly good recording performance was demonstrated on a non-initialized disc based on the DVD-RAM ver.2.0 format.

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We obtained the experimental exothermal curves of chalcogenide alloys Ge₄₀Sb₁₀Te₄₅Se_3.5M_1.5, M=Co, Cu, Ni, Pb, and applied the Kissinger's formula to extract the activation energy Ec. Our results indicate that the activation energy E_c, increases while doping a small amount of M metals. At isothermal electrical resistivity measurement, the resistivity of the sputtered doped films decreases with time. Also the esistivitry decrease rate (dR/dt) increases with the increase of isothermal temperature. This phenomenon is due to phase transition between amorphous and crystalline states. The crystallization process in our study is interpreted successfully by Johnson-Mehl-Avrami (JMA) transformation equation, and the crystallization time τ is extracted from the JMA equation when we compared the experimental results to the equation. We find that the crystallization time for Ge₄₀Sb₁₀Te₄₅Se₅ alloy with doping M is shorter significantly than that for Ge₄₀Sb₁₀Te₄₅Se₅ alloy without doping, and it is lower than 50 ns at 730 K and near 100 ns, respectively. These results indicate that the M dope enhances crystallization process.

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In order to increase storage capacity and data transfer rates, a sophisticated signal processing technology − multilevel technology − has been developed. To demonstrate the advantages of this novel technology, a multilevel (ML) optical data storage system that triples the capacity and transfer speed of CD systems has been realized. This article explains not only the basic system concept but also describes how the ML system has met the margins required for existing manufacturing processes.

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Conventional optical recording methods strive to write a pattern of “perfect marks” on the media, then process the resulting read wave form electronically (using filters, equalizers, slicers) to extract the lengths/positions of the recorded marks. We propose to invert this process by concentrating at first on the read process, deciding which wave forms the read channel can and should supply given its particular constraints (e.g., spectral content, bandwidth, noise characteristics, restrictions of the peak amplitude, etc.). Once the desired read waveforms have been identified, we suggest strategies for recording“patterns” (e.g,, amorphous/crystalline regions on phase-change media, magnetic domains on MO media) that can produce the desired waveforms during readout. By employing the heretofore forbidden mark/space patterns at the medium, the proposed analog schemes should be capable of delivering higher recording densities. Also, by allowing the system designer to match the read waveforms to channel characteristics, the proposed schemes should use the available SNR more efficiently.

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A new method for recording tamper-resistant and disc unique information to each ROM disc is proposed. A pulsed beam of the CW-Q switch type YAG laser is irradiated to a ROM disc. A laser spot is formed like a rectangular shape on a reflective film of the disc and removes it to form a stripe of 10μm width overlapping on pre-pits. By forming a series of the stripe on the disc circumference according to the phase encoded signal, 188-bytes information can be recorded. The recording method has been adopted as BCA (Burst Cutting Area) in the DVD standards.

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In the near future, Disc media will be used generally instead of Tape media for video recording. And at all kinds of High Density Optical Disc system, a high efficiency disc format is a common subject. In this paper, we propose a new addressing method for a High Density Digital Video Disc Recorder.

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This paper describes a lens system that enables one lens compatibility between next generation rewritable videodisk system and digital versatile disk (DVD). The lens system consists of a bi-aspherical single objective lens, a holographic optical element and spectral selective filter. The lens system has good aberration characteristics on the both system and the difference of the working distance is as small as 0.1 mm.

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We developed a new solid immersion mirror (SIM) for near-field optical data storage. The SIM has plano-convex shape similar to a single lens. Through an aperture of ∼300 nm in diameter on the focal point of the SIM surface, bit-data recording onto a photochromic thin film was realized. Size of the written spot was ∼300 nm, the same as the aperture diameter. This was the first report of writing data using a SIM with a small aperture.

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The magnetic head for Magnetic Field Modulation (MFM) recording on Magneto-optical (MO) disk rubs protective resin film. Therefore, it is required that the protective resin film has good lubrication and surface flatness to reduce the damage of disk and head. In this study, the protective resin film of a UV curable resin which can be formed by only one process has been developed for that purpose. As the result, it has been found that a UV curable resin film consists of mixture rate 60% epoxy novolac acrylate, 40% ethoxylated trimethylol propane triacrylate, 4% polyether modified silicone polymer and 4 % photoinitiator (total mixture rate 108 %) exhibits boundary lubrication of a fixed 0.04 coefficient of kinetic friction over 5 g load.

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This paper describes the improvements of the DC control characteristics and the simplification of the encoder for the new 8 to 15 rate RLL(2,10) constraint modulation, D8-15¹⁾. The results show that the improvements can effectively contribute to realize a high density optical recording.

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A new run-length-limited (RLL) code for dual-layered optical disks is described. It is an asymmetrical (d1, d2)=(2,1) code, i.e., its minimum mark length is three channel bits to maintain the readback signal power, and its minimum space length is two channel bits to maintain the partial-response maximum likelihood (PRML) performance. It encodes 8 user bits into 15 channel bits. The spectral density in the low-frequency band (lower than 1/200 of the Nyquist frequency) is lower than that of the EFM-Plus code.

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