The storage of machine-readable information is of fundamental importance in today's highly complex and computer-oriented society. Shipments of data storage peripherals in 1982 had a total value well in excess of $10 billion, and the strong demand for additional capacity is reflected in the high annual growth rate of this market.

Magnetic recording is entering yet another phase of explosive growth both in applications and in technology. Witness the 35mm magnetic camera and the excitement created by the rediscovery of vertical recording. Alternate technologies hoping to profit from its supposed demise (e.g.; optical storage) again see their emergence threatened. This paper addresses the prospects for the "moving target" - magnetic recording.

Optical disk provides a unique combination of performance characteristics that make it ideally suited for large memory applications. Application examples are given in imagery, document, and data storage.

A laboratory model optical disk file memory for digital data storage is developed. User storage capacity is 2GBytes per disk and data transfer rate is 350KBytes/sec. Average seek time is 150msec. Several new technologies supporting the device are also described in detail.

High sensitivity, long term stability recording medium of an amorphous Te-C filmand Buried Multi-Heterostructure (BMH) GaAlAs laser diodes with high output power and good optical quality for digital optical storage use have been developed.

An 800 gigabyte optical memory system has been demonstrated in two laboratory machines, tested in an engineering model, and is in final prototype construction. The system utilizes 5" square slides and a linear motion for read/write processing. An acousto-optic beam deflector is utilized in the optical system as a near diffraction-limited device to provide a scanned laser beam. The system architecture is discussed with particular emphasis on the electro-optical sub-system operation.

Nanosecond read, write and access times, system volumes of one cubic foot, and costs of 10^-8 cents per bit characterize this new volumetric optical technology.

The data processing applications which are most appropriate for optical storage are used to derive a set of user application requirements for optical storage products.

The Common File System (CFS) is a file management and file storage system for the Los Alamos National Laboratory's computer network. The CFS is organized as a hierarchical storage system: active files are stored on fast-access storage devices, larger, less active files are stored on slower, less expensive devices, and archival files are stored offline. Files are automatically moved between the various classes of storage by a file migration program that analyzes file activity, file size, and storage device capabilities. This has resulted in a cost-effective system that provides both fast access and large data storage capability (over 9 trillion bits currently stored). A large capacity (10¹⁴ bits), reliable Digital Optical Storage System would replace the offline storage as the archival part of the CFS and might also be used for active storage if it had a reasonable file access time.

This paper examines the current NCAR MSS, MSS use requirements, a possible optical systems design, MSS magnetic-to-optical conversion plans, and some cost considerations.

One of the problems in the area of user requirements for Mass Storage is the lack of clear definitions on: 1) the nature of user requirements, 2) desired hardware and software characteristics of future Mass Storage systems, 3) how future systems can be integrated into computing environments and, of special interest to vendors, 4) the size of the potential market for Mass Storage. A Mass Storage survey was prepared and distributed to collect information from potential users of mass storage for presentation to system designers. The results of the survey contained in this paper survey indicate some general trends in requirements and desired characteristics of new mass storage devices.

An optical disk configuration which uses coated webs is described. Full dust protection and handleability are provided in a sealed unit without compromising high performance.

The Sealed Disk Assembly (SDA) interfaces to an optical recorder in an unconventional manner. This paper describes a laboratory disk recorder which is designed to interface with the web-based SDA and gives some preliminary performance data.

Recording and playback of digital signals in organic media designed to be written with diode lasers and read out with visible or diode lasers is discussed.

The objective of this paper is to describe in general terms the physics surrounding the formation of an optical hole in a recording medium which is in intimate contact with an overcoat. The major thrust of this work involves the estimation of the thermal situation at the time of hole formation by the calculation of the temperature profile on the medium surface. Specific estimates of the activation temperature will be compared to experimental data gathered on read/write test equipment. Additionally, the optical properties of the resulting pit will be explored using calculations to estimate the pit reflectivity. The optical calculations are supported by experimental data from a read/write device. Transmission electron microscopy has been used to study the morphology of written holes and to elucidate the hole formation mechanism.

We have used gold with non-ablative hole formation mechanism for our recording media and have developed a process for optimization. The materials are highly sensitive, with long archival life and are overcoat compatible. The optical efficiency of the multiple layer recording structure can be optimized by simple optical monitoring. Uniformity of 14" planar disk coating can be achieved with proper masking technique.

Write once optical media are an attractive method of achieving high density archival information storage via optical DRAW techniques. Recently, emphasis on single laser diode read/write hardware recorders has been noted due to the increased reliability, simplicity, and lower hardware costs. The purpose of this paper, therefore, is to describe the laser diode performance characteristics of a new 1.5 GByte optical disk developed by 3M which features high sensitivity, high S/N, and preformatted, pregrooved protected plastic substrates.

Mechanical, Optical, Read/Write and Environmental guidelines for Optical Storage Media will be presented. The guidelines were created by a group of optical storage media and drive company representatives. The purpose of these guidelines is to assist others in optical media and/or drive design development and provide definitions and test methods for those interested in optical storage media.

A perspective on the evolution of ablative optical recording media is presented. The factors which lead to the development of efficient recording media and the mechanisms which govern pit formation are reviewed. Methods for monitoring pit formation in real time by reflection and transmission are described.

Hard carbon (diamond-like) thin films have been deposited on tellurium coated glass slides by ion beam techniques. Laser written holes have been obtained in these carbon film protected Te films with 16mW of power. The process of producing the carbon films on Te is described.

The optical characteristics of Sb₂Se₃ and Sb₂ Te ₃ films changed as a result of an amorphous crystalline phase transition below 200 °C. The respective reflectivity of 400 A Sb₂Se₃ and 300 A Sb₂Te₃ films, each on a Te reflective layer, increased from 10% to 30% and from 45% to 65% by laser radiation. The recording sensitivity of a disc is enhanced by using this unique double-layer structure which consists of a recording layer and a heat (laser) absorbing layer. A high-performance optical laser disc on which both digital and analog signals can be recorded by a diode laser has been developed using these newly developed, highly sensitive recording materials.

Theoretical analysis and a preliminary experimental result reveal a fundamental sensitivity advantage of textured media due to the absence of an energy barrier other than melting the material itself.

Optical recording characteristics of textured germanium show a systematic variation in the slope of contrast vs writing energy, as a function of sample production parameters. Textured surfaces have been studied for application to optical storage medial and represent an alternative mechanism to the usual ablative hole-opening process. The important advantage of the textured media is that the slope, S=dC/dE, in the contrast, C, vs writing power, E, curve can be easily altered by adopting various etching conditions in the texturing process.

Photochemical holes are burnt and detected in the inhomogeneously broadened 833 nm zero phonon line of the R' color center in LiF using current tuned GaAlAs diode lasers.

Major types of high power (15-50 mW cw) single-mode diode lasers are discussed. An individually addressable array of high-power CDH-LOC devices is presented.

Diffraction integrals are calculated for a distribution of CDH-LOC diode lasers to assess efficiency of matching them to fixed and variable magnification optical recording systems. High power diode lasers are characterized, in general, by far-fields having an elliptical cross-section. In addition, while the intensity profiles of these far-fields in the planes parallel and perpendicular to the plane of the semiconductor junction are often approximated as gaussians, the true far-fields may differ significantly from such a shape. The development of the constricted double heterojunction large optical cavity (CDH-LOC) diode laser at RCA Laboratories 3 has created a commercial device with applicability to optical recording in the near infrared. We have evaluated a sample of CDH-LOC's in order to determine how to tailor the optics of recording systems to utilize the output of the CDH-LOC device as advantageously as possible, i.e., high throughput efficiency and small spot diameter.

A review is made on the current status of the study of the self-coupling effects in the semiconductor laser diode and on the application of the effects in optical memory readout. It is proposed and demonstrated that the operational instsabilities caused excess coherency of the laser output light is suppressed by placing either a polarzation rotator or a phase plate in the path of the light.

We consider algebraic codes for the efficient storage of binary data on an optical disk. An [n,k.t] code will store k bits of data in n cells of memory t times. A [15,4.6] code is described that can increase the capacity of a disk by 60%.

We developed the Automatic Loop gain Control System of CD Player's tracking servo. It measures Frame error numbers with changing the loop gain in playback, and enlarges the loop gain by a fixed value from the loop gain when the error numbers increase suddenly. Consequently, we were able to decrease the lens actuator noise and to adjust the deviation of track loop gain by disc characteristics.

It is shown that focus error signal spectrum, measured while disk is spinning, represents Fourier transform of the disk profile modified by the loop gain.

A potentially low cost magneto-optical recorder for up to 10 MByte capacity on a 50 mm disk is investigated. The storage layer consists of an amorphous film such as GdTbFe. Information is written and readout by a low power AlGaAs semiconductor laser.

A new type of magneto-optical memory system using a chromium dioxide (Cr02) disk combined with a magnetic garnet film was described. Thermomagnetic recording was done onto the 35 cm diameter Cr0₂ disk with the focused Ar-laser beam and a recorded signal was read out magneto-optically through a magnetic garnet film placed close to the disk surface. A carrier-to-noise ratio of 35 dB was obtained at a disk speed of 50 m/s and frequency of 7 MHz. Track width of 3-4 μm was observed. A real time video recording experiment was successfully demonstrated.

The magneto-optical rotation (MOR) of amorphous rare earth-iron thin films with reflecting layers and the characteristics of magneto-optical disc exerciser are described. The MOR of GdTbFe thin films increased from 0.27° to 0.5° by the addition of Cu reflector , and to 0.65° by supplementing an SiO₂ intermediate film upon the Cu reflector. Furthermore in the case of a quadri-layer structure, which consisted of SiO, GdTbDyFe, SiO₂ and Cu layers, the angle of rotation was augmented to 1.75°. The Magneto-optical disc player, making use of the above quadri-layer structure disc, attained a carrier-to-noise ratio (CNR) of 40 dB at 2 MHz, thereby proving the applicability of the equipment to digital file memory systems.

Reflectivity, polar Kerr rotation, and magneto-optical (M-o) response of rf-sputtered amorphous TbFe thin films, overcoated with thermally evaporated SiO, were measured as a function of TbFe film thickness in the range 5-150 nm. The optical and tvi-o properties were found to depend strongly on film thickness and deviations from theoretical calculations were particularly large for very thin films. It was suggested that the complex dielectric tensor, and hence the index of refraction and absorption coefficient, vary with film thickness due to existence of an island-like/void microstructure for very thin films. The importance of an experimental determination of optical and M-O properties in relation to a theoretical computation was pointed out.

Magneto-optic (M-O) enhancement and dynamic recording characteristics of amorphous Tb-Fe thin film media were investigated for a bilayer and a quadrilayer structure. The results of the investigations on the M-O enhancement, using a static tester, show that an optimum M-O response in a bilayer structure media occurs at a TbFe film thickness of 20 nm, whereas for the quadrilayer, the optimum response occurs between 30 and 40 nm, depending on the thickness of intermediate SiO used. Comparison of the maximum M-O response in the two film structures shows that an increase in signal-to-noise ratio (S/N) up to 2dB can be achieved by using the quadrilayer structure. A saturation peak to peak signal to rms noise of up to 35 and 37 dB were measured respectively, for the bilayer and the quadrilayer films using the dynamic tester.

Accelerated ageing tests on discs with Te-alloy films for ablative digital optical recording show that these media meet the requirements for their applications in long-term data storage. In these tests, discs of the air-sandwich type with non-sealed (open) as well as sealed cavities were subjected to cyclic high temperatures (25-65°C) and high humidity (95% RH) conditions. "Open" discs incorporating pure Te as ablative material cannot with-stand such severe conditions for more than a few days whereas "open" discs applying Te-Se based alloys with 60 to 80% Te content have not reached end of life after 100 days storage under the same conditions. After such a period of accelerated ageing, hermetically sealed discs do not show any significant ageing effects at all. Ageing is defined in terms which are relevant to optical recording, such as sensitivity for writing, signal to noise ratio of written data and bit error rates and bit error distribution.

The resistance to oxidation and cracking of metal-Te-Se recording films and their mechanisms have been studied. The metals included In, Pb, Sn, Bi, and Sb. The films were deposited by multi-source, high-speed rotary evaporation on substrates with glass-U.V. light curing resin-cellulose nitrate or acetate structures. The role of Se is to inhibit the oxidation and the role of metallic elements are to inhibit cracking and to decrease noise in reproduced signals by making crystal grains smaller. Selection of substrate surface material, especially selection of U.V.light curing resin, is also important to avoid oxidation of the recording film. Depth profiles of the recording films have been analyzed by Auger electron spectroscopy and X-ray photoelectron spectroscopy to clarify the mechanisms of oxidation inhibition.

The stability of Te and Te-alloy films for optical data storage was studied both over a large area by using a uniformly illuminated light source and locally by using a scanning laser beam. These films are found to degrade uniformly, with limited localized degradation. The dominant degradation mechanism of thin Te films is the uniform oxidation of Te to an optically non-absorbing TeO₂. Localized degradation occurs only at regions where initial defects on the film or when conditions leading to water condensation on the surface of the film are present. Promising Te-based optical recording media with both excellent archival stability and reasonable laser writing characteristics have been developed from this study.