Our development of a production Electron Beam Recorder designed for making masters for optical discs of up to 100 gigabytes capacity is discussed. A second-generation electron beam column for this machine will also be discussed and some recent results of optical discs ranging in capacity from 4.7 GB to 100 GB will be presented.

We propose a method to record a multilevel signal onto an optical read only memory disc. In this method, we use the signal processing to generate the multilevel recording signal, which satisfies zero-intersymbol interference condition and zero-direct current condition. The resultant multilevel signal is emboss recorded as position displacement of groove walls. To playback a disc, the push- pull detection and the adaptive equalizer is used. Experimental disc of 0.6 micron trackpitch and a 0.28 micron/bit of density is made. When a DVD equivalent optical pickup is used to playback this disc, we confirm the error rate of 3 X 10^-4 and a clear 2D eye pattern of 16 levels.

For the DVR system with the use of a blue laser diode (wavelength 405 nm) we developed (12 cm) discs with a total capacity of 22.4 GB. The land/groove track pitch is 0.30 micrometers and the channel bit length is 87 nm. The DVR system uses a d equals 1 code. These phase change discs can be recorded at continuous angular velocity at a maximum of 50 Mbps user data rate (including all format and ECC overhead) and meet the system specifications. Fast growth determined phase change materials (FGM) are used for the active layer. In order to apply these FGM discs at small track pitch special attention has been paid to the issue of thermal cross-write. Finally routes towards higher capacities such as advanced bit detection schemes and the use of a smaller track pitch are considered. These show the feasibility in the near future of at least 26.0 GB on a disc for the DVR system with a blue laser diode.

The noise reduced disc and the advanced signal reproduction system with the asymmetry compensatory function enhance the disc capacity up to 19.8 GBytes per DVD size. The noise was reduced by applying Aluminum based multi-component alloy for the reflective layer, moreover all the loops in the system accurately function even under the signal asymmetric condition by using the newly developed Error Feedback type PRML. The error rate characteristics versus disc tilts suggest that the ROM disc system has sufficient performance for the practical use.

We prepared and tested a disc that has a transparent plastic substrate of 0.3 mm thickness to confirm the readout capability using a blue laser diode. And the test results of injection molding for the plastic substrate of 0.3 mm thickness are shown.

We developed a 1.5-Numerical-Aperture optical setup using a GaN blue-violet laser diode. We used a 1.0 mm-diameter super-hemispherical solid immersion lens, and optimized a phase-change disk structure including the cover layer by the method of MTF simulation. The disk surface was polished by tape burnishing technique. An eye-pattern of (1-7)-coded data at the linear density of 80 nm/bit was demonstrated on the phase-change disk below a 50 nm gap height, which was realized through our air-gap servo mechanism.

Optical disk readout based on direct optical feedback to a semiconductor laser is studied via simulations. Laser dynamics and the diffraction of light in the extremely short external cavity formed by the laser front facet and the optical disk surface are taken into account. We compute both the variation of the laser's output power and its oscillation spectrum versus the position of scanned data marks. The characteristics of the laser's spectral response versus flying height and versus laser facet reflectance variations are described. Techniques for achieving various types of enhanced playback are discussed.

The contributions to noises in optical disk readout caused by the surface roughness on the disk are calculated using a full vector diffraction theory. The sources of noise are assumed to be small periodic bumps existing on land or groove, as well as periodic jaggedness on the groove walls. Under these conditions, the polarization dependence of noise, the difference of noise when the bumps are on land or groove, and the depolarization noise in magneto-optical readout are calculated.

We describe a 3D model to numerically evaluate the transient optical field in the case of MSR (Magnetic Super-Resolution) media. The first part of the model calculates the temperature profile in the media due to optical heating. The second part of the model calculates the transient magnetic parameters as a result of the temperature change. The third part of the model performs a simulation of the magnetization dynamics as a result of the change in the magnetic parameters. The fourth part of the model simulates the optical field during the transient magnetization dynamics.

The shapes of phase-change marks on surface recording discs with a Substrate/Ag/lower ZnS-SiO₂/AgInSbTe/upper ZnS- SiO₂ layered structure were investigated by scanning electron microscopy (SEM). When the upper ZnS-SiO₂ layer was removed by a wet chemical process, the marks were clearly observed as dark contrast in the secondary-electron image mode. The SEM observation showed that the mark size could be reduced to around 0.1 micrometers in the tangential direction. The mark shapes were crescents, and fluctuation with scaling down was hardly visible. Uniform 0.1 micrometers marks made on surface recording discs which use AgInSbTe will allow an increase in disc capacity.

We have studied the crystallization behavior of stoichiometric GeSbTe versus (doped) eutectic SbTe materials. For pseudo-binary compositions on the GeTe-Sb₂Te₃ tie-line, the nucleation time and the complete erasure time (CET) of an amorphous mark are of the same order of magnitude, typically in the range 20 - 100 ns. For compositions close to the eutectic Sb₆₉Te₃₁ the nucleation time exceeds 100 microsecond(s) , 4 orders of magnitude longer than the CET. The nucleation probability of doped SbTe materials was determined experimentally and a low temperature maximum was observed, in line with classical nucleation theory. The large difference in the nucleation and growth rates of both material classes has important consequences for the erase mechanism of amorphous marks in practical phase change media: for stoichiometric GeSbTe materials mark erasure is nucleation-driven, whilst it is growth-driven for eutectic SbTe compositions. For growth- driven mark erasure, we observed a strong dependence of the CET on amorphous mark size. This dependence must be quantified, to be able to compare the crystallization speed of different growth-dominated materials. Therefore, we developed a method in which the size of a written amorphous mark was deduced from the measured modulation level.

In this paper, we develop a model for the statistical nature of nucleation in phase change recording media and use it to estimate the mark edge jitter arising from the nucleation process. We then investigate the dependence of mark edge jitter on the erase power and reflection layer thickness.

We have studied high-density magneto-optical recording using a Domain Wall Displacement Detection medium with a 664-nm wavelength laser diode and a 0.60-NA objective lens. Employing a wide-land structured disk and 16 - 17 modulation code, large recording/readout tolerances were obtained with a linear recording density of 0.11 micrometers /bit and an user data-transfer rate of 21 Mbit/sec. Furthermore, the feasibility of higher user data-transfer rate up to 50 Mbit/sec was studied.

We developed a DWDD (Domain Wall Displacement Detection) medium which was applied for an optical disk system with a blue laser diode ((lambda) equals 406 nm) and an objective lens of NA equals 0.60. the layer structure of the medium was modified by taking into account the thermal characteristics of the medium during readout with blue laser. The result of jitter measurement suggested that areal density of over 15 Gbit/inch² is feasible for the DWDD media with a blue laser.

We have investigated high density magneto-optical recording on a center aperture detection (CAD) type of magnetically induced super resolution (MSR) disk using a GaN blue laser diode. The substrate treatment by an ultraviolet rays irradiation, the optimum thermal structure, and the stabilization of copy process by tripled layer recording films were applied to improve the CAD-MSR media for a blue laser. The carrier to noise ratio of 0.227 micrometers mark length was 43 dB and the jitter without cross-talk from adjacent tracks was 10.3% at the areal density of 10.8 Gbit/in². We confirmed that a blue laser is the most promising method in order to realize the higher areal density for CAD-MSR disk.

A new high SNR readout method for quadri-valued MO recoding by detecting both MO rotation angle (theta) and ellipticity (eta) with only single wavelength is proposed. This advanced method is demonstrated by using a double-layered MO disk and green laser. Each layer of the double layered MO disk is independently read by an optical head for detecting (theta) and (eta) at 514.5 nm in wavelength.

We have developed a multi-beam light source using a passive device that narrows the optical spot pitch in a multi-beam optical head. It consists of an optical-fiber input system and an optical waveguide. Using an experimental multi-beam light source, we demonstrated optical output of 12 mW with a propagation efficiency of 30% and wave-front aberration of less than (lambda) /20. Although the mode type of the waveguide was multi-mode, we could focus the beam at the optical spot within the diffraction limit.

An understanding of the processes involved in direct overwriting (DOW) of phase-change optical recording media is vital in the development of new, and the improvement of existing, products. The present work investigates the microstructural and crystalline phase changes during overwriting of Ag-In-Sb-Te disks. Samples were prepared for observation in a transmission electron microscope from initialized disks written 1, 2, 10, 100 and 1000 times. After initialization, both bcc and fcc crystalline phases were observed, with a distinctive growth-dominated microstructure. After the first write (DOW(0)), a greater amount of the fcc phase was present within the groove, with an altered microstructure, against growth-dominated. A clear boundary between erased and as-initialized structures is observed. The second write (DOW(1)), produces a distorted mark shape, with a reduced amount of the fcc phase in the groove. After DOW (1000), again the mark shape is distorted, but now only the bcc remains within the groove. The phenomenon of jitter bump and the eventual failure of the disk are explained in terms of the differences in physical properties between these bcc and fcc crystalline phases.

We have developed a new technique for measuring pit geometry, track pitch, jitter and wobble on compact discs (CD) and digital versatile discs. This method uses direct physical inspection with a Atomic Force Microscope. The images are analyzed by our automated method and yield statistically robust results, so that process windows can be determined. In both types of media we report a variety of statistical parameters including mean and standard deviation and create trend charts and other graphs. In addition to the media previously mentioned we demonstrate imaging the data marks of a written CD-RW using surface potential.

Guided scrambling (GS) is proposed as channel coding for digital holographic data storage. Its property is investigated in the context of Fourier frequency domain. We show that GS provides, with a very small cost in terms of code redundancy, an effective tool for removing detrimental array patterns.

As densities of holographic storage increase, ISI and noise begin to severely limit data fidelity. The problem of ISI can be alleviated through at least two different techniques namely, equalization and low-pass encoding of the data. We study the relative merits of the two methods and quantify their benefit from a density improvement standpoint.

Data pages retrieved from a volume holographic storage channel (VHSC) suffer generally from two degradations: inter-symbol interference (ISI) and noise. ISI can be combatted by equalizers which are designed based on careful modeling of the VHSC. In this paper, we present an efficient model for volume holographic storage channels. Numerical simulations show that the developed model outputs are accurate.

The reflectivity of an amorphous mark on a first-surface phase-change optical storage disk is shown to vary with the level of crystallization of the GST layer. A static tester with 680-nm laser diode for writing amorphous marks and a 643-nm laser diode for monitoring the reflectivity changes is used for the experiment. An 8% difference in reflectivity is measured between the amorphous marks formed in the fully crystallized, high reflectivity (R equals 43%) state and partially crystallized, low reflectivity (R equals 30%) state.

High data rates of up to 180 Mbps were demonstrated in a magneto-optical recording system embedded in a 1/2 high 5 1/4' disc drive. Techniques and equipment enabling these high rates are described. Measurement techniques and data rate limitations are discussed.

Preliminary experimentation of angle-multiplexed high- efficiency volume holograms at 1550 nm is presented. It exploits two-color technique by recording digital bytes at 488 nm in iron-doped lithium niobate and retrieving them in near infrared. The stored database constitutes a first holographic memory for optical fiber communication systems.

As the computational speed of the central processing unit (CPU) is increased, the demand for high data rate memory is emphasized. Although many kinds of large capacity optical memory like one with near field optics are being studied, the data transfer rate of them will be still too low for it's disk capacity. Therefore, the optical cluster drive is realistic solution. because it is applicable to all kinds optical memory1'2 Therefore, it can be promising candidates for network server in the future. The precise analysis of the data integrity of the optical disk cluster drive has not be presented This paper describes the analysis on data integrity and reliability of it.

The track pitches of optical discs have become so narrow that it is comparable to the wavelength of laser beam. Finite-difference time-domain (FDTD) simulation, based on vector diffraction analysis, can predict the propagation of light more accurately than scalar analysis, when the size of media texture becomes sub-micron order. The authors applied FDTD simulation to land-and-groove optical disc models, and found out that the effects of 3D geometry is not negligible in analyzing the energy absorption of light inside the land- and-groove multi-layered media. The electromagnetic field in the media does not have the same intensity distribution as the incident beam. Furthermore, the heat conduction inside the media depends on the disc geometry, so the beam spots centered on land and groove makes different effects in heating the recording layers. That is, the spatial and historical profile of temperature requires 3D analysis for both incident light absorption and heat conduction. The difference in temperature profiles is applied to the phase change simulator to see the writing process of the marks in land and groove. We have integrated three simulators: FDTD analysis, heat conduction and phase change simulation. These simulators enabled to evaluate the differences in mark forming process between land and groove.

Monolithic multi-layer optical disks have been recorded with single-beam two-photon absorption using a high-repetition- rate laser. The recorded bit shape and signal readout will be discussed. It will also present some initial experimental results in cross talk and signal quality measurements.

Testing of servo error signal detection technique for 2- photon recorded monolithic multilayer material is investigated. A standard CD voice-coil actuator follows a fluorescent track.

We present a novel solution for high-density optical storage of data in thin media. The holographic memory card of Optilink provides sixty-fold data density enhancement compared to present commercial LaserCard devices. The 1 - 2 micrometers thin amorphous polyester storage film is capable of rewritable storage using a single laser source for writing and erasing. The polarization holographic principle used in reflection mode requires demanding optical solutions. Successful data evaluations prove applicability of the new system. Density enhancement up to 16 bit/micrometers ² with the use of 20 - 30 micrometers thick layer is also outlined.

A Magneto-Optical disk system, named iD photo (iD; image disk, intelligent disk) has been developed as next generation media for digital still cameras. It has a large recording capacity, 730 MB with a 50.8 mm diameter. It employs the field modulation method for recording and Center Aperture Detection type magnetic super resolution for reproducing. The media is designed to decrease the recording field so as to reduce electric power consumption for mobile use.

We studied a high areal density recording using a conventional disk on a blue MO system. To increase the areal density, we used mainly three techniques. First, we reduced a disk noise by UV irradiation. Second, we made CNR higher by adjusting the thickness of a metal layer to control the thermal conductivity. Third, we adopted an optical phase shift method for land and groove recording to increase the track density. Using these techniques on an optical pick-up with a 407 nm-Kr laser and a 0.6-NA objective lens, practical system margins were obtained at a 10 Gbit/inch² areal density.

Results of an ongoing project aimed at demonstrating optical recording densities of 100 Gb/in² are presented. The technologies focused on by the project include Solid Immersion Lenses (SIL), Center Aperture Detection Magnet Super Resolution media, Laser Pumped Magnetic Field Modulation recording, near field spot characterizations and turbo coding techniques. Significant progress towards achieving a 100 Gb/in² optical recording density has been made. A super-SIL has been designed and fabricated. The super-SIL has been characterized and integrated into a recording system.

We studied the performance of the center-aperture-detection type of magnetically induced super-resolution disk using a blue laser diode and an objective lens with a numerical aperture of 0.6. We confirmed the practicability of 11 Gbit/in² recording density by the evaluation of the system margins. The recording density we confirmed is equivalent to 15 GB user capacity on a 120-mm-sized disk. We can expect higher recording density by the reduction of the crosstalk.

At the joint ISOM/ODS in 1999 SONY and Philips proposed a new physical format for a third generation optical disc storage system: DVR, Digital Video Recording. The DVR system enables a storage capacity of at least 22 Gbytes with a data rate of 50 Mbit/s on a single layered re-writable optical disc. The main ingredients of the DVR system are the use of a blue laser (400 nm wavelength) and a high numerical aperture (NA equals 0.85) objective lens. For this purpose a new rigid two-element glass-2P replicated aspherical objective has been developed. The DVR physical standard is based on phase change technology, allowing for removable media with high data throughput and long lifetime, and optical pickups of low complexity. All channel and servo electronics have been breadboarded, conforming to the physical format for DVR. In this paper we present an overview of the DVR bit engine and pay special attention to newly developed components, such as a general purpose laser driver IC, a plastic beam shaper and a collimator actuator for spherical aberration control. We report the results of the format evaluation using this bit engine, and we briefly mention the coupling to the video recording application layer.

EFMCC is a runlength-limited (RLL) channel code with EFM- like RLL constraints, d equals 2 and k equals 10, which is constructed by combining two codes, a main code and a substitution code. Both codes operate on a byte-by-byte basis. The substitution code has a special structure, i.e., for each byte, there are two possible channel words, which have opposite parity and the same next-state in the finite- state machine of the EFMCC code. The benefits are: guaranteed DC-control, 4% higher efficiency than EFMPlus, and simple byte-oriented look-ahead DC-control encoding.

Turbo codes are being investigated for magnetic recording channels. In contrast, relatively less attention has been devoted to the investigation of turbo decoding methods for optical data storage channels. In this paper, we present the simulation results of the performance of turbo decoding techniques in a partial response equalized optical data storage channel with transition noise. Our simulation results show that turbo codes with iterative decoding are robust to mark edge jitter, showing only a modest SNR loss even for 15% transition noise.

The basic idea of edge delay symbols for copy protection in optical discs and its feasibility test were performed in this work. The presented study showed possibility of edge- delayed symbols as one of promising methods for copy protection of digital contents.

This paper describes the advancements we have made in developing objective lenses and actuators for Digital Video Recording (DVR), which we see as the third generation in optical disk recording. Two generations of DVR prototype systems are presented. The first is an actuator to adjust the inter-lens distance of the two-element objective lens for spherical aberration correction, mounted in a focus/tracking actuator. The second prototype is a more efficient and faster focus/tracking actuator with a rigid two-element objective lens accompanied with an adjustable collimator lens for spherical aberration correction. The latter system is implemented into a prototype bit-engine.

A new radial tilt detection method for rewritable optical disks using a 3-beam optical head has been developed. It features high-sensitivity characteristics and is suitable for high-frequency servo operation. Experimental results have demonstrated the validity of this method.

A mathematical model and computer codes are developed to reliably predict the motion and stability of optical pickups in optical disc servo systems.

The need for achieving high areal density in data storage devices that are smaller, cheaper and have faster access time has led to a number of new data storage and read-write technologies. Alternate substrate materials are being evaluated in order to achieve these goals. Plastic substrates offer exciting new possibilities in this area. The present study focuses on the understanding of dynamic performance of disks under loads typically seen in data storage applications. The role of substrate material damping in enhancing the dynamic performance is clearly established both analytically and experimentally. Simple analytical models were developed to predict the frequency and displacement of disks under dynamic loading (including the effects of material damping). The loss modulus of the material was identified as the main parameter that controls the damping behavior of the substrate material. The predicted response of the dynamic performance of disks was verified successfully through experiments. Results indicated that the analytical predictions agree well with experiments. The models developed in this study were used to develop materials with enhanced damping characteristics. These materials showed greatly improved vibration response and were comparable to the current substrate (aluminum) material.

This paper describes a design for a near field hybrid recording system that uses a mode index waveguide lens in place of a SIL or optical fiber. The mode index waveguide lens is fabricated on the back of an air bearing slider with a thin film magnetic head and giant magneto resistance (GMR) sensor for reading and writing. The optical spot from the waveguide heats the media to its Curie temperature such that within the spot a region with a reduced coercive field (`Curie cylinder') is created. The thin film head then applies a magnetic field to switch the magnetization within the Curie cylinder thereby recording a written mark. In the system proposed here, the track width of the optical spot is less than that of the thin film head and as such defines the recording track width. A GMR sensor is used to sense the flux leakage from the surface of the media and may also be laser assisted. Calculations predict an aerial density of 70 Gbits/inch² when using a simple mode index lens fabricated from a SiO₂/SiN_x/SiO₂ waveguide. Furthermore, by using advanced lens designs and innovative materials, the track width can be reduced further thereby offering a promising way to achieve 500 Gb/inch².

High speed overwriting capability of the nucleation-free and growth-dominant eutectic Ge(Sb₇₀Te₃₀)+Sb phase- change material, and its application to high speed overwritable DVD and CD, are discussed. The addition of Ge to Sb₇₀Te₃₀+Sb binary system could effectively suppress the nucleation in recrystallization process, while high Sb/Te ratio could realize a selective enhancement of crystalline growth-speed initiated from the boundary of an amorphous mark and its crystalline background. This resolved a trade-off in high speed erasure and archival stability of amorphous marks. Highly enhanced crystalline growth also caused serious recrystallization during amorphous mark formation, resulting in shrinkage of amorphous mark size (premature cooling issue). This premature cooling issue as well as premature heating issue, in multiple pulse strategy with such a short writing and cooling pulse as below 10 nsec at high clock frequency of > 100 MHz for over 4X speed rewritable DVD, were resolved with a 2T-period based multiple pulse strategy. Thus, feasibility of 2 - 4.8X CAV operatable rewritable DVD and 16X CD-RW was demonstrated.

A physical channel model of readback signals from a hybrid MO recording using magnetic flux detection is presented. The system performance has been investigated using the proposed model, together with the comparison of channel characteristics in the longitudinal, near field and hybrid architectures. Preliminary iterative decoding results with this channel model are also presented.

The Electrooptic Beam Scanner is a solid state device developed at Carnegie Mellon's Data Storage Systems Center (DSSC) that is capable of scanning a laser beam approximately +/- 1 - 3 degree(s) at frequencies of at least 200 kHz. The optical group of the DSSC is currently employing the scanner as a fine actuator for high performance optical data storage systems. This paper discusses several aspects of that research, including multi-track scanning for increased data rate, controller for two stage actuator systems, and feedforward control for ultra-fast seeks.

As densities of storage increase in holographic optical memories, ISI becomes an issue calling for efficient equalization techniques. We investigate the use of fixed delay tree-search (FDTS) as an economical alternative to the optimal but often complex solution of maximum likelihood sequence detection. We compare the two techniques from a performance and complexity perspective and show that the former is simpler to implement with limited loss in performance. We adapt fixed-delay tree search with partial response equalization to holographic storage and quantify SNR and density gains obtained from it. The benefit of low- pass codes used with FDTS is also investigated. A cumulative density improvement of 71% is shown to be feasible using FDTS for scatter-limited channels.