Characteristics of erasable optical recording based on phase changes in a storage medium are described and compared with corresponding features of magneto-optical recording.

Magneto-optic media provide an attractive method of achieving high density information storage. Two primary media characteristics have limited the practical implementation of magneto-optic technology: environmental data retention stability and high performance. In this paper, we present the dynamic performance, data retention stability, and environmental lifetime characteristics of a new high performance magneto-optic8media which has been demonstrated to achieve >50dB of. C/N for storage densities >4)(10 bits/inch with data rates up to 75 Mbit/sec. Coated on a plastic, pregrooved substrate, this high performance media has an expected lifetime of more than 8 years.

A compact magneto-optical disk having 500 times the capacity of a 5-1/4 inch floppy disk is used for coded data storage. Low error rates are attained by the utilization of advanced highly sensitive polarization detection optics and high quality recording media. These fields of technology are developed based on noise analysis of readout signals. The disk drive can write and erase data by sectors and also play the current "write-once" type optical disk. This disk/disk drive unit promises to enhance the storage capacity of current office automation and other information systems.

The stability of magnetooptic recording films based on rare earth - transition metal alloys has been investigated. Experimental results show two distinct degradation processes, one of which has been identified as oxidation of the active layer, the other of which appears to be a thermally activated relaxation of the microstructure. Performance data are presented for newly developed, stable structures which exhibit virtually unchanged 55-60 dB C/N ratios after annealing at 200 degrees centigrade in air. Environmental stability is discussed.

A mean-field modelfor amorphous rare earth-transition metal (RE-TM) alloys is developed and compared with available experimental data on GdCo-, GdFe-and TbFe- based alloys. The model assumes the existence of two iron subnetworks, one with ferromagnetic and the other with antiferromagnetic exchange coupling. The fraction of iron ions in each subnetwork and the magnetic moment of the TM ion are the only adjustable parameters of the model. Good agreement is obtained in all cases between the model calculations and the experimental data. Preliminary measurements of the magneto-optic Kerr effect on TbFe samples are also reported and the results are compared with the mean-field model predictions. A phenomenological model for the anisotropy energy density constant (Ku) is proposed and the results are tied to the mean-field model for calculations of domain wall properties. Finally, the magnetization reversal process and the nature of coercivity in thin films of TbFe are investigated, and the nucleation, growth, and stability of domains are discussed in terms of simple phenomenological models.

Characteristics are described on erasable magneto-optical(M0) memory disks using some plastic substrates of 200 mm 4id 120 mm with a 2.5 um pitch pregrooved. Static recording test was conducted for TbFeCo films deposited on plastic substrates with a He-Ne laser (A =633 nm) at a pulse duration of 1 us. In the case of PC (polycarbonate) substrate disk, a threshold power was 0.8 mW for recording a bit of 0.6 um in diameter. Recorded bit was smaller than in the case of PMMA(polymethyl methacrylate) substrate disk at the same power. This result can be considered that MO disk of PC substrate should be feasible for a high bit density memory disk. Following that, dynamic characteristics were also examined. The mean value of C/N (carrier to noise ratio) of 48dB was obtained at 1 MHz (z1f: 30kHz) for TbFeCo thin films on PMMA disks. Furthermore, TbFeCo MO thin film with a dielectric layer exhibited the value of 52 dB. In order to estimate the life time of MO disk, two type of disks were exposed under at constant temperature of 60 °C, and in constant moisture of 90% RH. Type (A) was constructed with [substrate/MO film/protector] and (B), [substrate/intermediate/ MO film/ protector] . In type (B) of PMMA disk, C/N measured by semiconductor laser (A =830 nm ) at 1 MHz, decreased by 5 dB compared to the initial state after a few days. In the case of PC substrate MO disk, on the other hand, type (A) disk exhibited long life time as compared with PMMA substrate. C/N ratio of type (B) of PC substrate disk had kept the initial state for two months. These results strongly suggest that PC substrate obtained from our new injection molding method should be suitable for MO disk substrate.

Selenium film alloyed with indium and antimony has good characteristics for erasable optical disk media. Depending on the conditions of the irradiation directed to the film, it exibits two different reflectances and geometrical deformations,.and the change between these two states is reversible. The mechanism of the reversible changes is different from amorphous-to-crystalline phase transition. Both states are definitely crystalline, which have been confirmed by transmission electron microscope analysis. The film has a good durability of write-erase cycles and is chemically stable. The disk sample has been confirmed to be capable of writing and erasing at a speed of 600 rpm. The resolution is sufficient to record a bit of 1 pm length on the disk. Carrier-to-noise ratio is fairly good. This film also has a potential for higher signal transfer rates.

Sn-Te-Se amorphous-crystalline phase change recording film is analyzed on write/erase cyclability, erasing speed, and activation energy of crystallization. The Sn-Te-Se thin film, sandwiched by two SiO2 thin film layers, is deposited on an organic-thick-film coated glass substrate. Then, another organic thick film is coated onto these layers. For these samples, the maximum erasure(crystallization) speed by laser beam irradiation and other write/erase characteristics are measured. Information can be written and erased more than 106 times. The crystallization activation energy is also measured and found to be about 2.3eV. The life of the amorphous state is estimated to be about 10 years at 40°C. These experimental results show that Sn-Te-Se thin film is promising as a reversible phase change recording film.

In recent years, we have systematically studied amorphous layer formation of III-V semi-conductor compounds irradiated by pulsed laser light. In this paper the study on the phase transition of semiconductor compounds and multicomponent alloys was reported. The optical properties of materials during phase transition were measured. The surface morphology,transition temperature and laser threshold power were also determined. A dynamic model for surface cooling and phase transition was proposed. The stability of amorphous layer were investigated in detail. The possibility of using these materials for reversible optical disc was discussed.

Various relations are presented between a number of process variables and the resultant properties of transition metal-rare earth films. In particular the bias voltage, target voltage and argon gas pressure are related to the film coercivity, compensation temperature, anisotropy and film thickness. The domain size obtained on writing in these films with a laser is given as a function of write field, anisotropy, coercivity, film thick-ness, bias, and laser pulse width. Domains as small as 0.4 μm are reported. The trends observed are explained.

This paper describes the principles of mastering as a means of preformatting recordable optical data storage disks with sector heading marks and tracking grooves. It is shown from calculations based on vectorial diffraction theory that optimum read-out signals are obtained from grooves wider than pits on read-only optical disks. Two methods to realize such wide grooves are indicated.

Precision electroforming in replication of optical discs is discussed with overview of electro-forming technology capabilities, limitations, and tolerance criteria. Use of expendable and reusable mandrels is treated along with techniques for resist master preparation and processing. A review of applications and common reasons for success and failure is offered. Problems such as tensile/compressive stress, roughness and flatness are discussed. Advice is given on approaches, classic and novel, for remedying and avoiding specific problems. An abridged process description of optical memory disk mold electroforming is presented from resist master through metallization and electroforming. Emphasis is placed on methods of achieving accuracy and quality assurance.

An optical recording disk employing an alloy mode mechanism has been developed. The disk is a plastic substrate on which a multilayer of four thin metallic films is formed by sputtering deposition. The first and the second layers on the substrate are the recording layers of Sb,Se, and Bi,Te,, respectively. The third is an adiabatic layer and the fourth e-rdflectivb layer. The disk is double-bonded; i.e., two disks are bonded together with protective and adhesive layers like a sandwich. The disk is recordable on one or both sides. A laser diode is used as the optical source for reading and writing. The laser beam scans the guide groove and address pits that have been embossed on the plastic substrate. The recording mechanism is based on multiple interference in the multilayer. When the laser beam heats the recording layers, the Sb2, Se3, and Bi2,Te3, form a four-element alloy by diffusion. Then the boundaries in the multilayer disappear to change the condition of initial multiple interference, which increases the reflectivity twice to2four times. The disk has high sensitivity and sharp cutoff at a laser power of 0.8nJ/μm2, below which the reflectivity does not change. The optimum recording power depends on the scanning velocity and pulse duration of the laser beam.

Sector servo optical disk mass data storage system was designed. In this method each track is divided into 1024 sectors. Each sector consists of the preformated servo field and data field where data are recorded. One forth wavelength depth preformated servo field contains wobbled pits array from which tracking servo signal is generated. This tracking error signal is sampled and hold in the data field. This system has advantages of its compactness of optical drives and higly improved optical stability.

A flexible automatic disk handling system has been developed for a small size optical disk jukebox storage. Although an optical disk can store a large number of data, single disk capacity is becoming insufficient. Easy data accessible compact size mass storage system is being intensely required for office use. A solution to such requirement is small size optical disk jukebox storage, which provides large data capacity in small storage area and allows various applications, especially in office automation. The disk handling accessor was developed for use in a compact optical disk jukebox engineering model. It can access 200 optical disks, which are aligned in two disk containers, arranged on both sides of the accessor. The disks are carried and stored without a cartridges. The accessor is able to carry a disk from its stored position to two or more disk read/write stations selectively in less than 7 seconds. It can also rotate the disk to allow both sides read/write operation. All moving elements, such as disk pickup arm, disk rotation mechanism and disk clamping mechanism, are gathered on one carriage, allowing flexible disk handling and making the accessor smaller and simpler. Using this accessor, all optical jukebox mechanism, including two disk containers and several disk read/write stations, are packed into rather small area of 0.4m2. Some new techniques for the optical disk storage and system architecture concepts of the jukebox storage system are also described in this paper.

An advanced optical disk recorder has been developed for very-high-performance data capture, data storage, and data sorting applications that cannot be cost-effectively addressed by alternate magnetic or optical recording systems. The recording approach uses a three-channel, argon laser-based optical system to input/ output user data at rates up to 100 Mbps and store up to 1011 userbits per side of a 14-inch disk. This is achieved at a disk rotation rate under 30 rps and at a corrected read-bit error rate less than 10-9 by the use of an efficient data encoding algorithm, read-while-write verification, and a two-level error detection and correction architecture. The automated disk handling method achieves less than six-second access to the data from 68 on-line disks, with provision made for future interface to an external storage module to achieve automated access to several hundred disks in under 15 seconds. The recorder design provides for a growth in capability to accommodate a.0-300 Mbps user data rate for a concentric data format on the disk or a fixed, continuous rate to 450 Mbps for a spiral format with a single nine-channel write/read head, to simultaneously write to or read from a double-sided disk, and to add a second turntable. Operational reliability and maintainability has been enhanced with respect to earlier recorder designs by providing 1) more convenient access to the optics and the disk-handling mechanisms, 2) optical system alignment control loops, 3) disk write power control loops, and 4) advanced subsystem status monitoring with software-controlled fault isolation.

Optical Disk Mass Storage Systems for rugged use in non-benevolent environments, such as tactical applications, are being developed by RCA. The new developments being reported in this paper are the addition of a monolithic array of individually addressable diode lasers as a source for dual-channel optical recording, and the refinement of the optical modules for rugged environments.

Using the Panafile 1000, we have developed an optical disk memory equipment which is capable of storing 15,000 sheets of the letter-size document data into an optical disk of 20 cm in diameter. Then, we also developed a system which is designed to handle 700 optical disks, corresponding to data of 0.525 Terabyte. We further developed a Terabyte Multi-Disk Deck which is capable of monolithically handling 500 disks (0.38 Terabyte) of the optical disk. This system and multi-disk deck are effective in storing and retrieving the hand-written or stamped documents corresponding to significant volume of data.

A new disk format and a new recorder were developed, based on the still picture disk file system which was put on the market a few years ago, whereby a video disk system that permits concurrent continuous recording of video and audio signals has been developed. In order to achieve a prolonged. recording time, the disk track pitch was narrowed from the conventional 2.5 μm to 1.6 μm and a contrivance was also made circuit-wise to eliminate the resulting cross talk interference. Because of these innovations, 13.3 minutes (24,000 frames) of continuous recording is now realized on a disk 20 cm in diameter. For a continuous recording of sound signals, a continuous track is necessary. To solve this problem, a spiral track was developed in lieu of the conventional concentric track. To indicate addresses, this track is locally interrupted. Such interruptions would normally interfere with sound recording but such interferences could be prevented by selecting the optimum relation between, the length of interruptions and the sound carrier frequency.

This paper describes an optical mass storage system being developed for extremely low cost distribution of small software packages. The structure of the media, design of the optical playback system, and some aspects of mastering and media production are discussed. This read only system is designed solely for the purpose of down loading code in a spooling fashion from the media to the host machine. The media is configured as a plastic card with dimensions 85 mm x 12 mm x 2mm. Each data region on a card is a rectangle 1.33 mm x 59.4 mm which carries up to 64 KB of user data. Cost estimates for production are $0.06 per card for the media and $38.00 for the playback device. The mastering process for the production tooling uses photolithography techniques and can provide production tooling within a few hours of software release. The playback mechanism is rugged and small, and does not require the use of any electromechanical servos.

Two optical disk "jukebox" mass memory storage systems have been developed that provide access to any data in a store of 1013 bits (1250 Gbytes) within six seconds. These engineering models have been developed under a program sponsored by the Air Force and NASA ana have recently been delivered to testbed facilities -- one to NASA Marshall Space Flight Center and one to the AF Rome Air Development Center. Each system contains a library of 125 optical disks with mechanisms for retrieving any disk, and recording or playing digital data at 50 Mb/s. Disks in protective cartridges are moved from the store to a load station, which then mounts the disks onto a precision turntable. Still in the cartridge, they are spun up to speed and data is recorded or played back via focused laser beams. The major emphasis in both the NASA and Air Force jukebox optical disk systems has been reliability of operation. Enhancements of the mechanical, electrical, and software designs have been implemented to minimize the user downtime in an operating scenario. The NASA system will interface to a database management system using a fiber optics data bus, while the Air Force system will interface to a DEC VAX 11/750 minicomputer. Both systems will store digitized imagery and provide fast access to a huge store of such images.

A description of the sampling schemes, as used in the Optimem 1000 optical disk drive, is given. These schemes are used to derive clock synchronization and servo data from preformatted features on the disk. This data is then processed to re-phase the system clock and provide error signals for the focusing and tracking servomechanisms, whose performance is indicated by oscilloscope photographs.

In a single beam read-write optical head, an astigmatic method using a cylindrical lens and a push-pull method are adopted for focusing and tracking error sensing, respectively. The disturbances for the servo sensing signals when the optical head records and reads along a pregrooved track, which has the depth of X/8 and is locally intermittent for address code, are compensated by signal processing technology.

An optical head for quick access and precise tracking servo has been developed. The head uses two independent one-dimensional lens actuators and a pair of relay lenses, instead of the conventional galvano mirror or two-dimensional lens actuator. This simple device is suitable to widen the higher-order resonance frequency and to apply the two-stage radial srevo which increases the tracking servo gain and range. The relay optics reduces the offset error caused by the deviation in the reflected back beam on 100 μm tracking to less than 0.1μm and enables the light source and detection parts to be separated from the positioner drive which carries only the lens actuators for access.

Charge coupled device (CCD) image sensors are used as detectors in a low capacity read only memory device. Because of the finite areas of the photodetectors in the CCD device, the output signals from the device can not reproduce exactly the original data. In this paper we discuss a signal processing method for reconstructing the original data from the imperfect CCD signals. Different channel encoding techniques for recording the digital data are also discussed.

Optical recording systems capable of information storage and retrieval, using a highly focused laser beam as the recording and playback source, have been developed to a point where products are introduced. Many varities of archival write once, or nonalterable, optical storage media have been proposed and developed. Reversible or erasable optical storage media have been the subject of research since the earliest days of optical recording. Many different wave shapes for encoding digital information are being used, each with its own application and limitations. If clock and data are derived from the read waveform, transitions must occur frequently enough to provide synchronization pulses for the clock. On the other hand, consecutive transitions must be far enough apart to limit the interference to an acceptable level for reliable detection. Due to this, the binary data is coded in binary sequences that correspond to waveforms in which the maximum and minimum distances between consecutive transitions are constrained by prescribed coding rules. In this paper the algorithms and properties of the major recording codes for optical recording are discussed. This can be used in connection with channel parameters to define the best encoding scheme for the particular case.

The optical recording media static characterizer (ORMSC) was constructed to aid in the initial development of near infrared photosensitive optical recording media. The ORMSC consists of an optical microscope to which a high power laser diode, diffraction-limited optics, and associated drive, control, and protection electronics have been added. A diffraction-limited spot is created on the optical recording medium which is placed on the microscope stage. Marks may be made on the medium while the operator observes through the eyepieces. All necessary power supplies, laser drive electronics and protection circuitry are built in. Scanning electron micrographs of various media have confirmed mark sizes of less than one micron diameter. The ORMSC has proven to be a dependable and useful tool.

The purpose of this paper is to describe a general purpose optical media evaluation system for erasable optical media samples. The thrust of the tester program is to determine the state-of-the-art of erasable optical media materials. The program is being sponsored by the Air Force at the Rome Air Development Center through the SBIR Program.

Many advances in flexible disk technology result from close cooperation between disk developer and the drive developers. While not ignoring progress in drives, this paper will emphasize the technological developments in disks. These developments are aimed at increasing the data capacity, the reliability, the durability and the range of operating temperatures and reducing manufacturing cost. The topics covered include developments in particulate and thin film coatings, the magnetic and non-magnetic properties of disks, the relative merits of longitudinal and perpendicular recording. Important trends are: a storage density (in bits/in2) which increases by a factor of ten every eight years, a widening in the range of operating temperatures and a greatly increased sensitivity to the protection of the disk and its durability. The paper concludes with a discussion of current problems, their possible limiting effect on progress and the possible future relationship of removable magnetic disks (flexible, Bernoulli, "stretched-surface" and rigid) reversible optical disks, and semi-conductor memories.

The recording density of a magnetic hard disk is potentially superior to that of an optical disk. It is also easier to reduce the price of a magnetic head than of an optical head because of the simple structure of the former. In industry, however, it is no easy matter to decrease head flying height from the submicron to the sub-submicron level because of head/media wear durability. Tribologv is the most important factor in the future development of magnetic disk stroage devices.

For over 30 years, digital tape has provided the most cost-effective medium for the storage of sequentially accessed data and for archival storage of large quantities of data. Tape will continue to meet all requirements in these areas because there are no plausible competing technologies and the current tape technology is not approaching any fundamental limits. Changes will be slow because of the inertia of existing tape libraries and the convenience of backward compatibility.

The 1990's generation of supercomputers could perform at a computational rate in excess of a Tera Operation Per Second (TOPS). for these very high performance supercomputers to be effectively used requires a new generation of peripheral storage devices. Based on present supercomputer storage capacities and transfer rates, the TOPS input/output (I/O) problem will be scoped. Methods for handling data in a realistic operational mode are examined along with strategies that could yield an acceptable solution. The elements of the solution includes hardware, data base software and special expert systems to manage the operational environment of the supercomputer complex. A NASA supercomputer complex will be used as examples of how design decisions impact the performance of the total system including the optical disk.

1985 will be the first year in which erasable optical memory drives and media are made available from numerous firms to beta sites around the world. Although volume availability of this technology is not expected until 1986 or 1987, public awareness of the potential of erasable optical storage should become widespread during 1985. Highlights of developments in optical memory technology in 1984 are reviewed as indicators of future trends, and predictions of the uses of erasable optical storage are offered. In addition, the results of a poll of industry leaders will be given listing their selection of the five most significant achievements of 1984 in optical memory technology.

Since 1974, Micromedex Inc., has authored and published three widely used medical databases on microfiche. An integrated medical database system has been designed to run on an IBM-PC compatible computer utilizing digital optical discs as the primary mass storage medium.

Bibliographic databases are quite large and relatively static, making them ideally suited for storage on optical media now becoming available. Consequently, libraries and publishing houses are pioneering certain applications of optical disks. The high storage density and the economy of optical disks make them attractive media for large databases. However, two factors create problems in the design of sophisticated retrieval software: certain device characteristics (e.g., slow access time compared to magnetic media), and the user interface requirements for bibliographic data. We discuss a prototypical application of optical disks to the publishing of the Library of Congress's machine-readable collection (the MARC and REMARC databases). The prototype disk is manufactured from pre-mastered videotape and is controlled by an IBM PC microcomputer. The prototype represents a significant effort in system integration, requiring development of hardware interface, error correction, low-level access software, high-level language interface, and user-friendly front-end applications. To prepare the data for indexing and display, mainframe software was developed. Based on our experience with the prototype, we discuss a number of issues common to the publication of such databases: data structures, search strategies, precomputation of retrieval results (a powerful technique well-suited to optical disk applications), and issues pertaining to standardization and publication formats.

Mass storage plays an increasingly important part in the changing role of the traditional open-shop computing center precipitated by the trend toward decentralization. A large number of mass storage applications are of the write-once type, for which the emerging optical disk technology is well suited. Some of the broad application areas are experiment data capture, shared reference data bases, program and documentation libraries, and medical studies requiring individual patient data. The utility of currently available optical disk products is being investigated for these applications for a variety of computing environments including those of IBM tm, DEC-VAX tm, and UNIX tm products.

Current medical practice needs images as a major diagnostical tool. However, as clearly demonstrated in some cases, the storage and retrieval of medical images becomes a growing problem. The volume of images and the problems to make extra copies contribute to this problem. Rapid developments in technology indicate the feasibility of an Image Information System (IMAGIS), coupled to the existing Dutch Hospital Information System ("ZIS"), by which functions as archiving, communication, processing and representation of medical image data can be realized. Such a system, however, incorporates such a complexity, that its realization can only be achieved through several stages of development. One of the very first stages can be the set-up of a digital mass data storage part. Hereby the evolution of optical storage media (digital optical disks and jukeboxes containing them) seems much promising, taking into account data lifetime and price/performance characteristics of storage media. The division of the storage part of an IMAGIS prototype into multiple layers seems inevitable, because of performance characteristics of the various storage devices available. A computer simulation model can be of great help to determine the composition of a storage configuration and of the algorithms for assignment of images to a specific layer. In order to meet future trends in technology a simulation model has been constructed with adjustable parameters. In the model each component, which is simulated, is assigned a process description giving in detail the actions a component has to perform, related to the actions of other components. An attractive configuration may be obtained by a systematic choice of different sets of parameter values. The input of the simulation model is derived from technical data and data representing the current use of medical images. This implies the need for knowledge of when and how often a medical image is requested, of the time a medical specialist examines the image etc. Part of this knowledge can be obtained by using the information available in the existing Hospital Information System, developed by BAZIS, and being applied in 20 hospitals in the Netherlands (11,500 beds together). Preliminary simulation results presented illustrate the usefulness of our problem approach, bringing the realization of an IMAGIS prototype one step further.