A holographic data storage prototype fully integrated with electronics for video demonstration has been developed. It can record data in several tracks of a photopolymer disk and access them arbitrarily during retrieving process from the continuously rotating disk. An embedded controller operates all of the optomechanical components of the prototype automatically and electronic parts conduct adaptive data readout of channel data up to 55 megabit per sec. For real-time video demonstration, video stream are recorded in four concentric circular tracks of the disk. Each recording spot contains about one hundred pages with angle multiplexing. The eleven minute length video data are successfully reconstructed from the prototype.

In this study, small sized optical pickup corresponding to blu-ray disc specifications has been developed in the array using wafer level packaging technology and verified that signal balance was satisfied with specifications.

We design and fabricate polarization-dependent components (PDCs) based on all-dielectric, fully planarized, multilayer microstructures of 150 nm period by using low-loss materials. Quarter-wave and half-wave phase plates at 405 nm are presented. Wafer-level retardation within +/-7deg of the targets and wavefront distortion at 10mm-aperture <20mλ rms are achieved. We also discussed the reliability of various composite microstructures. Stress-test up to 2000 hours at 85°C and 85% relative humidity confirmed that even air-channeled microstructures surpass very stringent reliability requirements. Multifunction integrated diffractive PDCs are discussed.

Phase masks are used to eliminate the Fourier-plane hotspot that otherwise degrades holographic data storage performance. In order to eliminate the cost, bulk, and precision alignment difficulties of inserting a discrete phase mask into an optical system we have designed phase masks integrated directly into the structure of a spatial light modulator used as the storage system's write head. A micron-thick ferroelectric liquid crystal film is confined between the surface of a VLSI integrated circuit and a window containing planarized relief structures on its inward-facing surface. This arrangement avoids depth-of-field problems encountered by designs that place the phase mask on the outer surface of the window. Any of a variety of phase mask designs can be implemented in this fashion. An alternative architecture in which pixel surfaces of the CMOS VLSI backplane are etched to differing heights is also investigated.

A folded solid immersion mirror for heat assisted magnetic recording was designed. The key components were fabricated and tested. By separating the incident light and reflected light with a directional coupler, high numerical aperture focusing can be achieved with small side lobes and high energy efficiency.

A newly optical pickup using integrated optical unit (IOU) which can detect spherical aberration error signal (SAES) and control light intensity distribution is described. In this IOU, the SAES is detected by hologram and light intensity distribution is controlled by grating. In addition, spherical aberration (SA) servo for a dual-layer Blu-ray disc is demonstrated by using this SAES.

When the multi-layer disc is read by a normal optical pickup, the signal light that is reflected in the read-out layer contains stray light from the adjacent recording layers, which is called the layer cross-talk (LCT). To reduce the LCT, we developed a new optical pickup that has a segmented wave-plate made of an auto-cloned photonic crystal. It has some advantages of perfect removal of LCT, detection of the high efficiency of the signal light, and the miniaturization of the optical pickup. In addition, by using this optical pickup, we confirmed the improvement of the signal performance, using a HD DVD dual-layer disc that has a thin spacer layer thickness, to increase the LCT.

We have ever demonstrated an optical disc system with the capacity of 100 Gbyte over and with the user transfer rate of 100 Mbps over, using near-field optics with a solid immersion lens of a 1.8-NA or more. In this paper, we introduce and discuss some technologies toward the removability of a near-field optical disc drive system.

Near-field induced polarization imaging with a solid immersion lens (SIL) is used to provide high lateral resolution compared with conventional far-field microscopy. In addition, a new technique is used to obtain height information from the near-field induced polarization (cross polarized) image. Several optical data storage samples, including DVD-R, DVD-RW, BD-RW, are studied with this imaging technique. A calibration target indicates an accuracy of ±2nm for obtaining height information.

Gap servo systems based on one of near field technologies are generally using the 1-beam push pull method to generate servo signal and this causes the optical DC offset problem in servo signal. In this paper, we presented new method of track error generation using the proposed GELP signal for the gap servo near field optical storage systems. By using the GELP signal and 2-divided photo-detector for the gap error signal detection, test result shows the optical DC offset in track error signal generated from lens movement could be eliminated.

We present our progress on the development of a single-wavelength near-field recording system with a blue-violet laser and a NA=1.45 Solid Immersion Lens in a conventional 3D actuator. We will introduce our near-field optical recorder and present good recording results achieved on discs with a 3 μm thick spin-coated protective polymer cover-layer using a channel bit length of 43.7 nm. Furthermore, we will show recent results on high-speed near-field readout, up to 3xBD speeds, through a cover-layer using feed-forward control in the air gap servo system.

A spin coating technique for the 100 micron cover layer for Blu-Ray Disc production has been developed. The process includes a controlled manipulation of the viscosity of the lacquer with heat and UV light during spin coating. Stability and cost efficiency, two vital criteria for mass production, have been considered.

We have succeeded in developing 6-layer write once disc for Blu-ray Disc system with 150 GB capacity per single side disc by use of a novel recording material: germanium oxide doped bismuth peroxide. By optimizing the compositions of the recording films and the layer structure, the jitters of less than 8.0% at the user data recording rate of 72 Mbit/sec were obtained by the application of the write power of less than 16 mW. The write power is low enough to use the commercially available blue laser diodes.

We report experimental results on amorphization and crystallization dynamics of reversible phase-change (PC) thin-film samples, GeSbTe and GeBiTe, for optical disk data storage. The investigation was conducted with subnanosecond laser pulses using a pump-and-probe configuration. Amorphization of the crystalline films could be achieved with a single subnanosecond laser pulse; the amorphization dynamics follows closely the temperature kinetics induced in the irradiated spot. As for crystallization of the samples initially in the amorphous state, a single subnanosecond pulse was found to be insufficient to fully crystallize the irradiated spot, but we could crystallize the PC film (in the area under the focused spot) by applying multiple short pulses. Our multi-pulse studies reveal that the GeSbTe crystallization is dominated by the growth of nuclei whose initial formation is slow but, once formed, their subsequent growth (under a sequence of subnanosecond pulses) happens quickly. In the case of GeBiTe samples, the crystalline nuclei appear to be present in the material initially, as they grow immediately upon illumination with laser pulses. Whereas our amorphous GeSbTe samples required ~200 pulses for full crystallization, for GeBiTe samples approximately 15 pulses sufficed.

Progress is reported on cover-layer incident Near-Field Recording. Very good recording results are obtained on a CuSi disc demonstrating excellent signal quality with modulation corresponding to the full effective numerical aperture of 1.45. Comparing the Near-Field system with Blu-ray Disc further shows that an extension to at least 4 data layers should be possible. In addition, a method for dynamic tilt control is presented. Controlling the tilt between the solid immersion lens and the disc surface improves the system robustness and relaxes media manufacturing tolerances for a roadmap towards 500 GB capacity on a single-sided, 4-layer disc which is protected by a polymer cover-layer.

The hemisphere type SIL of KTaO₃ that has a high refractive index was developed. NA 1.84 was achieved by the hemisphere SIL of KTaO₃ that has a wide thickness tolerance in combination with a high NA aspherical lens of NA 0.77. Huge capacities ROM of 50-100 GB were evaluated by means of KTaO₃ hemisphere SIL. The same playback performance as that of LAH79 SIL was confirmed.

We describe and characterize an active height control system for near-field data storage applications using a commercial laser diode as a direct position sensor. The self-mixing interference signal was experimentally characterized and the effective spot size of the laser sensor was also measured. A control system utilizing interference in the laser as feedback signal was constructed to drive a conventional DVD pickup with the laser sensor mounted. The residual position error is ±9nm when the rotation speed of a glass disk was 1500rpm and the vertical runout was 16μm. The approach limit was estimated to be 25nm when the laser size is reduced to 100μm.

We present a study on the feasibility of extending our current experimental cover-incident near-field recording system to a 4-layer system promising 500 GB storage capacity on a single sided 12 cm disc. We calculated the electromagnetic field inside a 4-layer disc of which the design was optimized to have a minimum in the irradiance near recording layers other than the one that the light is focused on. Furthermore an objective lens and compensation device were designed to accommodate writing and reading from all four layers.

Numerical simulations of the signal decay with media shift were performed. Principle of the shift selectivity of the data pages are explained with our simple numerical model. Decay of the diffracted signal is calculated with the shift of the media. The dependencies of the shift selectivity on the reference pixel patterns, radius and width of the of the reference pixel area, and the media thickness. Shift selectivity of the page does not depend on the media thickness or reference pixel patterns. It is mainly determined by the radius and the width of the reference pixel area.

In this study, we analyze and compare the performance of fixed threshold detection, adaptive threshold detection, log likelihood ratio (LLR) detection and iterative decision feedback equalizer (DFE) detection methods for holographic data storage (HDS) systems using real data pages as well as simulated data pages. Fixed threshold detector is popular because of its simplicity. Its performance is good when the amount of noise and inter-symbol interference (ISI) is low. Adaptive threshold is useful as a benchmark to compare the performance of other single-bit detectors, but is really not practical. LLR detector makes a decision based on bit probabilities and in that sense is an optimal detector when the input symbols are equally likely. LLR detector is usually used in combination with an iterative soft decoder. Iterative DFE detector takes into account the influence of the neighboring bits and the two dimensional (2D) ISI. Therefore an iterative DFE detector is a good detector candidate for HDS. The four detectors are tested with real data pages as well as simulated data pages. The results show that iterative DFE-based detector works well, even for data pages with low signal-to-noise ratio (SNR).

A unique coaxial optical system which enables us to record and retrieve the holographic data on a continuously rotating disc is proposed. The system supports an image-stabilizing technique and several servo mechanisms.

During the past five years, advances in the information-theoretic analysis of "one-dimensional (1D)" recording channels have clarified the limits on linear densities that can be achieved by track-oriented magnetic and optical storage technologies. Channel architectures incorporating powerful codes, such as turbo codes and low-density parity-check codes, have been shown to achieve performance very close to the information-theoretic limits. As 1D track-oriented data storage technologies reach maturity, there is increasing interest in "two-dimensional (2D)" recording technologies, such as two-dimensional optical storage (TwoDOS) and holographic storage. This paper provides an overview of some recently developed techniques for determining analytical bounds and simulation-based estimates for achievable densities of such 2D recording channels, as well as some recently proposed signal processing and coding methods that can move system performance closer to the information-theoretic limits.

For the optical recording channel, a new runlength-limited (RLL) code is proposed, called the 1102PC code, which is a d=1 RLL code with a compact 2-to-3 PCWA-mapping for DC-control that offers a significant performance benefit over traditional soft-decodable d=1, k=7 codes thanks to the reduced frequency of occurrence of the shortest 2T-runs as realized via an r=2 RMTR-constraint; in addition, it still offers a low k-constraint (k=10) and a SISO-complexity much lower than that of 17PP. The 1102PC code has also been evaluated experimentally for near-field optical recording.

A novel timing recovery for read channel systems with asynchronous full-digital architecture is presented. The timing recovery consists of a frequency synthesizer and digital circuits employing an adaptive oversampling rate controller to keep its oversampling rate constant. Therefore, it is no need to change a digital equalizer characteristic even if a data transfer rate varies. Moreover, it controls the power consumption to be adequate at CAV. Since the proposed timing recovery is constructed of full-digital logic, it can realize a robust read channel system in high-speed signal processing and on next generation LSIs.

Radial tilt adjustment method with Partial Response Signal-to-Noise Ratio (PRSNR) was newly developed. This method is able to adjust radial tilt rapidly, because the method uses the detected signal with polarity to radial tilt. Furthermore, the method has the accuracy of adjustment within ±0.1 degree, which is enough for HD DVD.

Media considerations for a multiple-layered system using conventional thin films are presented in detail. The media are designed and fabricated for various geometries of thin film coatings to satisfy the optimum media condition minimizing inter-layer crosstalk for conventional reflective volumetric optical data storage systems.

High-density multilayer optical disc storage was investigated by employing advanced signal processing methods such as adaptive equalization and adaptive partial-response maximum-likelihood (PRML) detection. Preliminary experiments, recording on single-layer and dual-layer Blu-ray discs (BD), indicate storage capability of 33.3 GB/layer with adaptive 5-tap PRML. A new signal qualification method, sequenced amplitude margin quasi-error estimation (SAMQES), was introduced for high-density multilayer recording, and possibility toward a total storage capacity of 200 GB was examined by using a six-layer BD-Recordable disc. Despite coherent interlayer crosstalk and lower signal-to-noise ratio, SAMQES showed moderate increase from those in single-layer recording.

In a volumetric optical disc medium, two counter-propagating light beams focusing to the same point create a diffraction-limited size micro-reflector. We propose a single-sided optical layout for a three-dimensional optical disc recording system using the micro-reflectors. Calculation results of readout signal characteristics, estimation of interlayer crosstalk noise, and recording density of Micro-Reflector three-dimensional optical disc recording are described.

This article will describe a series of experiments we conducted for the purpose of pursuing the resolution limit of the PTM process. Disc samples with different track pitches and different linear densities were prepared through the PTM process. The signal properties of these discs were analyzed with the assistance of a near field readout system. The jitter value was 5.6% at the linear density of 70nm/bit and 0.16μm track pitch, which corresponded to 80GB per 12cm diameter disc. Even at a recording density corresponding to a capacity of 100GB we observed jitter values less than 10%.

We report the error rate improvement of super-resolution near field structure (Super-RENS) write-once read-many (WORM) disk at a blue laser optical system. (Laser wavelength 405nm, numerical aperture 0.85) We used a disk of which carrier level (CL) of 75nm is improved from -26.3 dBm to -19.0 dBm. We controlled the equalization (EQ) profile characteristics and used the adaptive 5 symbol write strategy and advanced high tap partial-response maximum likelihood (PRML) technique in order to improve the bit error rate (bER) characteristics of the super-RENS random signal. As a result, we obtained bER of 10^-4 level with new signal processing techniques and bit error analysis process. This result shows high feasibility of super-RENS technology for practical use in the near future.

In this paper we propose a multiphysics simulation of Super-Resolution BD ROM disk readout. Local metallization of the thin semiconductive layer deposited on a ROM substrate comprising a monotone sequence of 100 nm pits has been modelized by applying a Drude nonlinearity to the optical properties of the material. The photo-induced creation of free carriers lifted to the conduction band is assumed to be responsible for a local change in the optical properties of the active layer, making possible the detection of a far-field signal corresponding to pits smaller than the diffraction limit at a high readout power.

Holographic data storage materials are currently being developed at General Electric. These materials are based on a thermoplastic host doped with narrow-band absorption dyes. The dyes are photosensitive and undergo non-reversible photochromic reactions upon exposure. Samples were produced using different dyes and various concentrations in a polycarbonate host with a focus on sensitivity and capacity of the media. A challenging obstacle for a successful photochromic system is the inherent remaining photosensitivity of the material after the writing process. This paper will introduce the concept of a highly sensitive yet non-volatile photochromic data storage system. The chromophore is subjected to a post-treatment step at a second wavelength which removes the photosensitivity. The stored data can therefore be secured against degradation during read-out at the writing wavelength.

This paper updates the recent progress in the micro-holographic format data recorded in our second-generation dye-doped thermoplastic medium. This new medium is about 400 times more sensitive than our first generation material, while our single-bit system needs less than 2.3 milliseconds to write a micro-hologram. The characteristics of micro-holograms recorded in the high sensitivity material are presented and compared to earlier results from the first-generation low-sensitivity material.

Tilt tolerance of media is compared for bit-based and page-based holographic storage systems having an equal diffraction efficiency per bit detector, dynamic range of the medium and surface recording density. We have formalized the diffraction efficiency degradation caused by aberrations of a reconstructing reference beam induced by tilt of the medium, using a coupled wave theory in the Fourier domain. The bit-based holographic storage system has a larger media tilt tolerance compared to a page-based system with relatively large page size.

We propose a new wide-band laser noise cancel technique which is especially effective in Blu-ray Disc system because of its laser noise increasing compared with conventional optical disc systems. Laser noise cancellation method has already been available, but it is difficult to extend the noise suppression bandwidth for high-speed reading. So we examined the realization possibility of wide-band noise canceling and developed a new photo diode IC (PDIC) with noise cancel function based on our principle examinations. Big advantages in respect of the cost and space are expected to be obtained by adopting this technology.

We developed a new one-beam detection method with changeable multi division patterns, pairing with tangential spot size detection (SSD) method for focusing error detection. The changeable multi division patterns are realized by the active device, which consists of a non-polarizing HOE for tangential SSD method, liquid crystal (LC) active rotator and two different division patterns of layered polarizing blazed HOEs. The LC active rotator properly acts as the mode selector and an R/RE mode pattern for one-beam push-pull method and a ROM mode pattern for differential phase detection (DPD) method can be selected only changing the applied voltage. The newly developed system can derive one-beam push-pull signal, DPD signal, wobble signal and RF signal from the output only from five common photo detectors. Sufficient quality of these signals is experimentally confirmed. The one-beam push-pull signal is hardly affected by the stray light from other layers. The traversing noise of its focusing error signal is stably low even with high push-pull media and possibly large astigmatism. Its focusing error signal turns out to be much more stable and less influenced by groove traverses. In addition, we present a vision for next-generation slim and compact integrated optics with dual LC cells, which consist of the LC attenuator, laser noise reduction technology, and the LC mode selector, as explained above.

We have developed an objective lens which can be used for different optical disk formats -Blu-ray Disc, DVD and CD. The compatible technique is based on the diffraction characteristics optimized by tuning refractive index dispersion. This optical configuration can provide suitable designs for optical pick-up system of high speed recording.

We developed a negative-type photoresist of WOx film and obtained a low noise groove. We also confirmed a feasibility of the transmissive stamper using the WOx film for multi-layer discs.

Surface plasmon propagation properties for nano-sized metal aperture and nano-wire structures are studied based on the waveguide theory. It is verified that there are only TM₀ and HE₁ mode existing in both structures. For nano-wire structure, however, there is no cut-off radii for both TM₀ and HE₁ mode. On the contrast, there is a cut-off radius for nano-sized silver aperture structure, and even more, there are several characteristic radius coefficients a/ λ, -0.32, 0.73. For each section, the EM wave may takes on different features, e.g., totally-bounded features along the aperture interface for a/ λ >0.73, or oscillation inside core or strong attenuation along z direction for 0.32<a/ λ<0.73). HE₁ mode of metal aperture doesn't show cut-off radius as well, but the wave-number along z direction monotonically increase with the radius coefficient a/ λ in contrast with existence of a characteristic radius coefficient a/ λ of 0.41 for nano-wire.

Selecting a binary compound (Sb-Te, Zn-Sb and Ge-Te) with its composition at around a eutectic point generated a better super-resolution effect. The thickness optimization of the super-resolution readout layer was also effective for the property improvement. The temperature estimation indicated thinner the layer thickness is better as far as the readout laser can easily increase its temperature.

Two structures super-resolution near-field phase-change optical disks with masks Sb₂ Te₃ layer and a thermal shield layer in front of the mask layer on Blu-ray substrates were studied theoretically and experimentally. Optical simulation was conducted and the modulation transfer function (MTF) was calculated. MTF calculation results has revealed that the super-RENS optical disk exhibited the maximum response when nearly half of the laser spot was covered by the mask. The thermal simulation was used to find the optimum condition meaning that half of the laser beam is covered by the aperture on the mask layer. The recording signal and thermal stability on different structures were measured and analyzed. The simulation results are in good agreement with the experiment results.

This paper reports a new super-resolution, "saturated" imaging method using a flat slab of photonic crystal with negative refraction. The photonic crystal has hexagonal lattice with holes in dielectric material with an index of 3.6. When the operating normalized frequency is around 0.30, the effective refractive index is -1. Such a flat slab lens can tolerate disk deformation of approximately one-wavelength or more while maintaining the same super-resolution as the near-field imaging of the photonic crystal slab. The object distance can be as large as twice the slab thickness, and the resolution is about 0.43λ.

The crystallization characteristics and recording mechanism of the a-Si (20nm)/Ni (5 nm) bilayer recording film have been studied. Upon heating, the formation of the metastable NiSi phase occurred at about 200^oC, followed by the formation of the thermodynamically favored NiSi₂ phase at ~ 400^oC, and the crystallization of a-Si mediated by the Ni silicides below 600^oC, indicating that inserting a thin Ni layer could effectively reduce the crystallization temperature of a-Si. As Si atoms of approximately 92 at% were consumed by NiSi₂ phase formation, the reflectivity increase of the a-Si/Ni bilayer recording film was contributed to the formation of NiSi₂ phase. The activation energy for Ni silicide formation was determined to be 1.98 eV. The a-Si/Ni bilayer exhibited an optical contrast of 20% and abosrptance of 54%, which can provide high enough CNR and adequate recording sensitivity. After irradiated by a 405 nm blue laser pulse, a recording mark consisting of NiSi₂ was clearly formed in the a-Si/Ni bilayer. Under the dynamic test, CNR of 37 dB was achieved at a recording power of 4 mW, demonstrating that the a-Si/Ni bilayer recording film shows a great potential for use in write-once Blu-ray disk.

We have studied an increasing areal density with applying novel signal processing and pulse erasing writing strategy on the BD dual layer optical disc and demonstrated the feasibility for recording 66GB and 70GB per disc. As a result, we confirmed that applied technologies would allow increase recording density by 30% with commercially available disc.

The addition of Al increases the temperature and activation energy of crystallization of the fast-growth type Sb₇₀Te₃₀ recording film so that the archival stability will be improved. Meanwhile, the addition of Al increases the temperature and activation energy of melting of the Sb₇₀Te₃₀ recording film so that the local melting of the crystalline Sb and Sb₂Te₃ phases will be suppressed. The pulsed laser powers required to trigger crystallization, melting, and ablation of Sb₇₀Te₃₀ recording film increase with increasing Al content indicating the increased stability of the non-crystalline phase, in the meantime, the increased melting and ablation powers indicating the Al addition could increase the melting temperature and prevent ablation effect of the Sb₇₀Te₃₀ recording film.

Two methods are developed to determine the crystallization parameters of phase change materials on mark formation in phase change optical recording. Both methods are based on the comparison of experimental and numerical modeling results. In the first method, the shape of short written marks is compared in experiment and simulation. In the second method, long marks are partially erased. The resulted mark shape reveals information on the crystallization parameter. The set of crystallization properties in the simulation that gives the best match between experimental and numerical results can describe the crystallization behavior of the phase change material. The determined crystallization parameters and model give excellent predictions on mark formation and erasure in growth-dominated phase change materials.

The external feedback effect on the relative intensity noise characteristics of 405 nm InAlGaN laser diode has been analyzed taking into account the spontaneous emission noise and the high frequency modulation of the injection current. A Langevin diffusion model was exploited to characterize its relative intensity noise. The spontaneous emission noise components were quantitatively evaluated from the optical gain properties of the InAlGaN multiple quantum well active regions by using the multiband Hamiltonian for the strained wurtzite crystals. The extracted parameters were applied to the rate equations taking into account the external feedback and external current modulation effects. The simulation results were investigated to optimize the relative intensity noise characteristics.

A novel technique is presented for the computation of the polarization transfer function of optical assemblies with finite reflection coefficients, birefringence, and other parasitic imperfections. The methodology is directly applicable to optical data storage modeling, such as CD/DVD recording optics and the physical recording process.

A portable USB2.0 personal storage device that uses built-in encryption and allows data access through biometric scanning of a finger print is described. Biometric image derived templates are stored on the removable 32 mm write once (WO) media. The encrypted templates travel with the disc and allow access to the data providing the biometric feature (e.g. the finger itself) is present. The device also allows for export and import of the templates under secure key exchange protocols. The storage system is built around the small form factor optical engine that uses a tilt arm rotary actuator and front surface media.

A new high efficient DC-free 3-ary run-length limited (RLL) code for 3-level optical recording system is presented. Signal processing techniques, partial-response maximum-likelihood (PRML), which is used for recovery data from readout signal, is discussed.

Multi-level run-length-limited (ML-RLL) modulation on optical storage channels is a promising method to increase the recording density effectively. In this paper, some experimental results of 4-level RLL modulation on digital versatile disc (DVD) read-only discs are firstly presented. A new DC-free 4-ary RLL (2, 8) code with code rate of 8/10 (bits/symbol) is designed, and partial-response maximum-likelihood (PRML) detection is used to evaluate the bit error rate (BER) performance of multi-level readout signals. Experimental and simulation results show the feasibility of 4-level RLL modulation on DVD channels.

Practical optics for a cover-layer incident dual-layer disc with an NA=1.45 hemispherical solid immersion lens are designed, using a spherical aberration compensating liquid crystal cell. A hybrid servo system, gap servo for NA >1 and focus servo for NA < 1, is proposed.

An ordinary half-height size optical pickup with high light-use efficiency for Blu-ray Discs (BDs) has been realized. It has two objective lenses arranged tangentially. Although one of the objective lenses, BD objective lens, does not follow the line that passes thorough the center of the spindle motor, stable tracking-error detection has been achieved by enhancing a one-beam method. This pickup has a beam shaper which changes a divergent angle of light with high magnification. Although beam shapers are sensitive to a positional error, our pickup accomplished stable positioning by introducing a new structure.

In this study, a commercial BD (Blu-ray disc) and BD optics (blue laser and NA0.85) were used for multilevel recording. The goal is to double both the present capacity and data transfer rate. To achieve this, it is necessary to overcome severe inter-symbol interference (ISI) from outer cells at a small cell length. In order to suppress ISI, we have developed an advanced data detection method that uses CBDD (Cell Boundary Data Detection) and TCM (Trellis-Coded-Modulation), and have achieved an areal density of 34.6-Gbit/in² multilevel recording.

The influence of the interface layer to the chemical and electronic states of a phase-change recording material, GeBiTe (GBT) alloy, used in the high-speed rewritable HD DVD media was investigated for the first time using the hard x-ray photoelectron spectroscopy (HX-PES). The density of states (DOS) for the valence band of the amorphous state without an interface layer was smaller than that of the crystalline state. The band-edge energy of the amorphous state without an interface layer was lower by about 0.5 eV than that of the crystalline state. On the other hand, the DOS and the band-edge energy of the amorphous state of GBT with interface layers were almost same as that of the crystalline state, respectively. This result may lead to almost the same career density for electrical conduction for the crystal as the amorphous, which is totally unexpected thus very interesting because the atomic arrangements should differ from each other. We speculate that this effect is a factor for a high-speed crystallization.

50GB BD-R media with Te-O-Pd recording material was estimated to have a life expectancy of over 500 years according to acceleration test under stressed conditions. This stable recording material will reduce the possibility to lose important data even in sever storage environment.