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A linear channel model and a linear signal processing technique are available for a holographic data storage channel when our proposed coherent addition technique is applied to the reproduction process. As a result, the signal-to-noise ratio (SNR) after zero-interpixel-interference (IPI) equalization is markedly improved. Moreover, we can achieve a higher transfer rate at a lower oversampling rate owing to the almost ideal linearity of the reproduced signal.

The cut-off frequency was extended by a factor of more than two using a magneto-optical disk with thermally induced mask.

A super resolution has been achieved in the magneto-optical disk using an exchange-coupled multilayer film. Two types of magnetically induced super resolution, front aperture detection and rear aperture detection have been successfully investigated. A high C/N of more than 42 dB is obtained experimentally for a mark length of 0.3 micrometers which is much shorter than the resolution limit expected from the conventional diffraction theory.

The linear density of an optical disk is limited within the cut-off spatial frequency which is determined by the spot size of a focused beam. If the spot size is effectively reduced by using new technology, a remarkable improvement in the density could be achieved. Still more, combining with the technology of shorter wavelength laser could result in more than one order development.

In the conventional optical disk systems, the optical cut-off frequency is limited by the numerical aperture(NA) of the objective lens and the wavelength of the light source due to the diffraction.

Holographic memory surpasses all other optical memories in both data density and data-transfer rate-but its development has lagged behind disk technologies. The coaxial recording method may enable holography to become an integral part of the optical storage marketplace of the future.

Strained Si n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated on the Si0.83Ge0.17 relaxed thin layer formed by ion implantation technique. Although the SiGe thickness was as small as 100nm, the relaxation was highly enhanced thanks to the pre-ion-implantation into the Si substrate and the strained Si channel with very smooth surface was obtained. A nMOSFET was fabricated in this structure and 100% drive current improvement and 60% mobility enhancement over the control Si MOSFET were achieved. This indicates that the ion implantation technique is very promising for realization of relaxed-SiGe-based devices with very high performances.

We describe a coaxial holographic recording system for achieving high recording density. We implement several techniques, such as an objective lens with high numerical aperture (NA), high capacity page data format, a random binary phase mask, and an optical noise reduction element. Our system successfully realizes a hologram recording/retrieving at a low diffraction efficiency less than 2.0 x 10(-3) and achieves a raw data density of 180 Gbit/in.(2), thus demonstrating the potential of a coaxial holographic system for high-density optical storage systems.

Multiply-bonded tetranuclear complexes M2Pd2Cl2(pyphos)4 (1) and dinuclear complexes M2(pyphos)4 (2)(a, M = Mo; b, M = Cr; pyphos = 6-diphenylphosphino-2-pyridonate) are found to exhibit large hyperpolarizability γ of nonlinear optical property by using the picosecond degenerate four-wave mixing (DFWM) method; the γ values of 1a (1.5 × 10−30 esu), 1b (5.2 × 10−31 esu), and 2a (6.9 × 10−31 esu) are greater than those (ca. 10−35—10−33 esu) of transition metal poly(yne) polymers.

Strain-relaxed thin SiGe layers grown on ion-implanted Si substrates were evaluated by X-ray diffraction reciprocal space mapping and spatially resolved micro-Raman spectroscopy. It was found that implantation-induced defects effectively facilitated the misfit dislocation generation and multiplication during postannealing after growth, leading to large and homogeneous strain relaxation. While in-plane strain-field fluctuation with crosshatch morphology was clearly observed in the SiGe layer without implantation, a very uniform strain distribution without such morphology was realized in the sample with implantation. These results indicate that the ion implantation method is a very promising approach for realization of high-quality and extremely thin buffer layers.

Premastered optical disk by superresolution (PSR) for practical use has been achieved for the first time. The PSR disk has a phase-change material Ge2Sb2Te5 with stoichiometric composition. Superresolution results from a high contrast ratio of reflectance in the light spot between highly reflective crystal region and lowly reflective melted region. A high C/N ratio of 56 dB is obtained at a pit length of 0.4 µm using PSR. The C/N ratio is still as high as 50 dB for a pit length of 0.3 µm. The PSR disk with double linear densities of current CD is successfully read out with a clear eye pattern and a low error rate using current optics.

High-density magneto-optical (MO) recording using a land/groove structured domain wall displacement detection (DWDD) medium has been achieved with a digital versatile disc (DVD) dimensional optical head including a 664-nm wavelength laser diode and a 0.60-NA objective lens. Due to the deep groove depth, easy domain wall displacement is obtained without the use of a track boundary postannealing process. Sufficient readout performance is obtained in experiments at an areal recording density of 11 Gbit/inch2, which is obtained using a 0.13-µm bit length and a 0.45-µm track pitch. This areal density corresponds to a capacity of 15 GB per one 120-mm-diameter disk.

We have examined two unique data error causes for domain wall displacement detection (DWDD) media, dropout and bit shift, using 8–9 modulation and (1, 7)-RLL modulation. We have determined that dropout depends only on the mark length of recorded data, while the deviation of edge shifts, which causes bit shifts, maintains approximately the same value regardless of mark length. Using these characteristics of error causes, we have also shown a prospect of achieving several-tens-nm/bit recordings.

We report the results of magneto-optical (MO) detection using an optical phase shifter and a deep land/groove disk. We measured the recording characteristics in the direction of incident linear polarization and found that polarization perpendicular to the groove is best for a deep groove disk. Using perpendicular polarization, with a 693 nm wavelength diode laser and a 0.55-NA objective lens, sufficient readout and recording margins to guard against optical errors were obtained by the experiments at an area density of 3.69 Gbit/in2, which was obtained using a 0.35-µm bit length and a 0.5-µm track pitch.

We adopted mark position recording in order to cancel ghost signals which appear in domain wall displacement detection. We obtained a jitter of 6.8 % at a linear velocity of 1.5 m / sec for a bit length of 0.15 μm and a track pitch of 0.85 μm using a conventional optical pickup. We confirmed that readout and recording power tolerances are ± 22 % and ± 24 %, respectively, at an areal density of 5.0 Gbit / inch2.

We report the results of magneto-optical (MO) detection using an optical phase shifter in land/groove recording. We found that the MO detection method improves not only readout carrier level but also cross-talk characteristics against optical errors. Using this method with a 693-nm wavelength diode laser and a 0.55-NA objective lens, sufficient readout margins against optical errors were experimentally obtained at a 3.69-Gbit/in2 areal density, which yielded a 0.35-µm bit length and a 0.5-µm track pitch. Recording with a track density 1.4 times higher was achieved by introducing a 640-nm wavelength diode laser, a 0.7-NA objective lens, and a 0.258-µm bit length and yielded an areal density of 6.95 Gbit/in2.

We detected bits sized at 0.237 µm bit length and 0.85 µm track pitch recorded by magnetic field modulation on a magneto-optical disk with a 690-nm laser diode and 0.60-numerical-aperture-objective using a partial-response maximum-likelihood detection method. We confirmed that the optimum partial-response for this high linear density had four coefficients of 1 by analyzing difference metrics of error critical paths. The recorded bits with areal density of 5.6 bit/µm2 were also detected at a low error rate, which combination is 0.237-µm bit length and 0.75-µm track pitch. Its write power tolerance is limited to ±22%.

SNR of a polycarbonate MO disk with a narrow track of 0.85 μm and with a quadrilayer structure was improved by optimizing and improving the groove geometry, film composition / thickness, and birefringence of the substrate. By using a 690 nm LD, an NA of 0.55, magnetic field modulation, and RLL(1,7) coding, a high areal recording density of 2.5 Gbit/in2 was obtained. Moreover, the PRML detection of PR(1,2,1) increased the density up to 2.9 Gbit/in2.

Premastered optical disk by superresolution (PSR) using rear aperture detection (RAD) has been realized. The PSR disk has a chalcogenide material. Using PSR by RAD with a current CD system, we demonstrated the feasibility of increasing both the linear density and the track density of read only memory (ROM) optical disks. By superresolution in the linear direction, a high C/N of 47 dB was obtained for a pit length of 0.3 µm which is beyond the optical limit. Furthermore, by superresolution in the track direction, a low crosstalk of -38 dB and a wider margin of radial skew angle compared to conventional detection were obtained for a track pitch of 1.1 µm.

In view of the recent progress in visible lasers for next-generation optical disks, we describe the influence of source wavelength, aberration, and noise on eye-diagram jitter, which determines the ultimate disk density. The analysis indicates that the sources used in a readout of a 6× areal density, (4,22) run-length-limited code with a minimum mark length of 0.4 µm must have a wavelength that satisfies the Nyquist condition of relationship between the spot size and the minimum mark length, a wave-front aberration of less than 0.035 rms λ, and relative intensity noise of less than -125 dB/Hz.

Tripled areal density optical recording was realized with the combination of a high power laser-diode pumped intracavity frequency-doubled Nd:YAG laser (SHG green laser), a low noise GdFeCo/TbFeCo double-layered magneto-optical (MO) disk, and high sensitivity photodetectors optimized for the wavelength of the light source. A high carrier-to-noise (C/N) ratio of more than 48 dB and a bit error rate of less than 3×10-6 by (2, 7) run-length-limited (RLL) mark position recording was obtained at a mark length of 0.45 µm (0.6 µm/bit) for a disk with a 0.9 µm track pitch.

Magnetically induced super resolution (MSR) is a new technology developed by us. It more than doubles the readout resolution limit of a conventional optical disk system without shortening the laser wavelength or increasing the numerical aperture (N.A.) of the objective lens. We examined the characteristics of the readout signals of an MSR-by-RAD (rear aperture detection) disk and obtained a high C/N of more than 49 dB and good stability of the edge position at a mark length of 0.4 µm. We investigated the high-density MO disk system using the MSR-by-RAD disk. Owing to optimization of the writing process and waveform equalization, the system achieved a byte error rate of less than 10-4 at a bit length of 0.3 µm. This bit length corresponds to a linear density more than three times higher than that of the conventional 130-mm MO disk system of the ISO standard.

MSR (Magnetically induced Super Resolution) by FAD (Front Aperture Detection) was demonstrated by the readout waveform of the isolated pit. We calculated the response of the readout signal employing both the thermal analysis and the scaler detection theory. As experiments carried out with the same condition of the simulation, we obtained a favorable agreement between the experimental results and the simulation results.