RCA has designed, built, and tested an Engineering Development Model (EDM) optical disk drive. This ruggedized, 14 inch magneto-optic erasable/reusable disk drive is capable of storing 10 gigabytes of user data per double sided optical disk, at data transfer rates up to 50 Mbitisec. This EDM disk drive represents a major step towards the development of a fully qualified MIL-E-5400 erasable 14 inch optical disk mass storage system.
A high speed accessing 5.25-inch half-height MO ( magneto-optical ) disk drive has been developed. Average accessing time in the absence of latency is 26 ms. A split optical system with a swing-arm tracking actuator made it possible to realize such high speed accessing. In addition, this MO disk drive can provide the formatted data storage capacity of more than 300 MB.
A new design approach is presented for developing low cost multi-function Magneto-Optical Micro-Disk subsystems. The Modified Gilbert Model is proposed to describe statistically the measured error occurrence in the optically reproduced signal. It considers the dimensional characteristics of media defects by analyzing the reproduced signal and data errors. Using this analysis, a defect proof scheme is proposed which employs on-the-fly sector back-up area. Design concepts for 90 mm class optical micro disk subsystem are discussed briefly and a prototype is described.
This paper describes servo technology for the improvement of data transfer rate and access time in a high-speed optical disk drive. First, read-write characteristics of the continuous composite servo format and the sampled servo format are discussed in terms of the recording power conditions needed to achieve a stable data read-out. Next, An optical head with the laser diode and optics separated from the positioner carriage is presented. The separated optical head's tracking servo stability and spot collimating performance are discussed. Finally, a new two-dimensional rotary lens actuator with a high resonant frequency is proposed.
An optical-card reader/writer optical and electronic breadboard system, developed by SRI International under contract to Drexler Technology, is described. The optical card, which is the same size as a credit card, can contain more than 2 megabytes of digital user data, which may also include preformatted tracking information and preformatted data. The data layout on the card is similar to that on a floppy disk, with each track containing a header and clocking information. The design of this optical reader/writer system for optical cards is explained. Design of the optical card system entails a number of unique issues: To accommodate both laser-recorded and mass-duplicated information, the system must be compatible with preencoded information, which implies a larger-than-normal spot size (5 gm) and a detection system that can read both types of optical patterns. Cost-reduction considerations led to selection of a birefringent protection layer, which dictated a nonstandard optical system. The non-polarization-sensitive optics use an off-axis approach to detection. An LED illumination system makes it possible to read multiple tracks.
A Matsushita Technics SL-P10 compact disc player has been successfully converted into a prototype magneto-optical disk drive. The project demonstrates the feasibility of dynamic read and write using low cost, currently available components. Specific modifications to the compact disc player optics and electronics include: (1) the optical pickup, (2) the tracking servo, (3) the signal amplifier, (4) the continuous linear velocity rough servo, (5) the laser driver, and (6) the addition of a bias field electromagnet. The prototype still retains the ability to read from a compact disc. Music (encoded in the compact disc digital audio format) has been recorded and played back. Quantitative measurements of the system are presented, including spectrum analyzer traces of noise levels and data from recording single frequencies. An optical computer disk drive (CD ROM) and a compact disc digital audioplayer share similar optical pickup sections and thus the modifications described in this paper can be utilized for both the audio and the computer data applications. The prototype may be used as a test apparatus for optimizing media performance and conducting media lifetime tests.
A phase-shifting Mach-Zehnder interferometer was used to measure wavefront phase errors for an uncollimated laser diode source. The axial separation of the beam waists was then computed from the measured wavefront astigmatism and compared with directly measured values and the manufacturer's specifications. An optical disk head was also measured and the focused spot profile was calculated from the measured wavefront and beam apodization. The calculated profile was then compared with spot size measurements using a knife edge scanner.
The application of magnetic bearing technology to both the read/write head and rotary spindle of an optical disk buffer will allow its use in a spacecraft environment. An optical disk buffer concept can provide gigabit-per-second data rates and terabit capacity through the use of arrays of solid state lasers applied to a stack of erasable/reusable optical disks. The disks are fixed to a common shaft and each disk surface is served by an independent electro-optic module for recording, playback, and erasure of data. A magneto-optic technique is used to implement the record/erase cycle. The RCA optical disk buffer has evoked interest by NASA for space applications. The porous graphite air bearings in the rotary spindle as well as those used in the linear translation of the read/write head would be replaced by magnetic bearings or mechanical (ball or roller) bearings. Based upon past experience, roller or ball bearings for the translation stages are not feasible. Unsatisfactory, although limited, experience exists with ball bearing spindles also. Magnetic bearings, however, appear ideally suited for both applications. The use of magnetic bearings is advantageous in the optical disk buffer because of the absence of physical contact between the rotating and stationary members. This frictionless operation leads to extended life and reduced drag. The manufacturing tolerances that are required to fabricate magnetic bearings would also be relaxed from those required for precision ball and gas bearings. Since magnetic bearings require no lubricant, they are inherently compatible with a space (vacuum) environment. Magnetic bearings also allow the dynamics of the rotor/bearing system to be altered through the use of active control. This provides the potential for reduced vibration, extended regions of stable operation, and more precise control of position.
Our objective in this extended abstract is twofold: i) to present some results of a new model for vector diffraction calculations based on multiple Fast Fourier Transforms (FFTs) and ii) to introduce a new focus error detection scheme using a specially designed "ring lens".
Elements of the read path of a magneto-optic (MO) storage device are the lens that focuses the light onto the disk, the interaction with the disk, the propagation back through the objective lens, the polarization optics, and the detectors. This paper describes a program that simulates the effect of several disk parameters on the signal and noise of the read path. The program uses a scalar diffraction model and incorporates geometrical and optical properties of the disk, such as groove shape, signal pattern, and defects. An estimate of the signal current as a function of time is generated by the spot scanning along a length of the simulated disk that has an MO signal pattern and noise written on it. The signal calculated from the diffracted fields provides an estimate of the power spectrum, to which the effects of shot noise and amplifier noise are added to provide a total description of the read path.
Laser-feedback noise has important negative ramifications for the design of magneto-optical media and system performance. However, with appropriate noise-suppression techniques, its consequences can be minimized. This paper models laser noise in a magneto-optical drive and discusses four possible methods for reducing its effects. Finally, experimental results are presented.
In the shot noise limited case C/N-ratios of more than 60 dB should be achievable with MO-layers available today. Light ellipticity due to substrate birefringence and phase retardation in the optics reduces the C/N-ratio in practice drastically. With optimized optical set-ups C/N-ratios of 50-54 dB were realized with PC-disks. Local variations of substrate birefringence causes also specific hard errors characterized by peak error amplitudes much higher than the MO-signal. Such errors affect the design of the electronics of the read channel which is demonstrated by a Byte error analysis.
WORM (write-once-read-many) disk is a modern optical storage technology capable of storing large quantities of digitized information. The two major factors which determine the data storage density and the maximum read and write rates are the WORM optical head performance and the quality of the WORM disk. In this paper the effect of some system parameters and imperfections on the WORM optical read signal is studied.
The number of bit errors in magneto-optical disks were reduced and a bit-error rate of 10-6 was achieved even after an accelerated lifetime test. To reduce the number of bit errors, we performed error detection and classification and found that the substrate was the dominant cause of errors. The substrate we used was a photopolymer(2P)-glass substrate, and we found two types of defect origin. One of them was due to 2P residues on the stamper, and the other was due to dust adhering to the substrate. We reduced the initial bit-error rate by removing these defects. We also found that 2P impurities considerably increase the bit-error rate during the accelerated lifetime test. By purifying the 2P, we made our disks more stable, and estimated that their lifetime would exceed 20 years at 40°C and 90% RH.
A statistical model has been designed to interpret experimental burst error data in determining an optimal error management strategy for optical media. The model is based on the theory of a Non-homogeneous Poisson Point Process. The assumptions for the evaluation of defects capable of causing error bursts in a user's data stream (burst starts and burst lengths) will be discussed. With this model it is possible to determine the optimal error management strategy to achieve any desired system performance, including depth of interleaving, error correcting capability and certification fencing for excessively long error bursts.
Not only the maximum attainable linear density and the efficiency of a modulation code, but also the complete error picture of the code should be considered when optimizing a design for a high performance disk drive. Operating reliably at a particular density and data rate requires that the sum of all timing errors is less than the data window. These timing errors are noise jitter, errors due to the write process, and electronic errors. Disk capacity as a func-tion of data rate is shown to be a useful measure of the overall effectiveness of a code. In a first step, the analog signals of critical patterns of different codes were digitized and their associated noise levels measured. In an error picture simulation, the influence of filter and differentiator on the waveform was observed, and the signal to noise (S/N) ratio and the noise jitter were calculated. Timing errors due to the write process and electronics were estimated. The effects of rotation speed and data rate were simulated. On condition that all timing errors fit exactly into the data window, the maximum attainable data rate was determined. In a second step, the data rate and data density were verified experimentally. The data density versus data rate curves were determined for the EFM code (pulse edge detection), the RLL 2.7 code (pulse peak detection) and the 4/15 code (differential detection).
In order to develop good error-control coding strategies for a read/write optical disk it is necessary to know the error characteristics of the media. Since the technology is in its genesis, empirical information on the error traits is not available. It is thus necessary to base the design of coding strategies on projected behavior and similar, well-established technologies. We examine the generation of a suitable error control strategy for an optical disk buffer which is to be used for the temporary or archival storage of large quantities of data. The buffer consists of multiple, read/write, magneto-optic surfaces which are independently accessable. Information is stored in a spiral eight-bit wide track; thus an appropriate error-control code must be capable of correcting symbol and burst errors. The properties of Reed-Solomon codes, which are well known for their packet protection capabilites, are considered for such an application. Since there are multiple surfaces, we present the possibility of coding across the surfaces. With this type of coding an entire surface can be lost without destroying the integrity of the data. Intermittent operation of a read/write device such as a laser could be corrected, thus providing a graceful degradation of operation. The interaction of independent access and simultaneous read/write capabilites with the coding scheme is considered.
A versatile and precise pre-grooove writer, used to fabricate optical disk replication masters, has been developed. This paper describes some of the features and the structure of the pre-groove writer. The writer can produce both concentric and spiral grooves with a track pitch accuracy of less than 0.1 μm, on disks ranging between 3.5" and 12" in diameter. Concentric grooves can be written as fast as 10000 tracks per hour. A dual-beam optical system enables writing of disks of both the on-land recording and on-groove recording types.The mechanical components, position control systems and optical systems were all designed with the aim of attaining these characteristics.
Two new types of stampers have been developed in order to improve the quality of optical discs and to simplify the process for manufacturing stampers. One is a plastic stamper which consists of a PMMA substrate and a photo-polymer resin layer having fine patterns such as pits and grooves on its surface. The other is a quartz stamper which has the pits and grooves with different depth formed on the surface of the quartz substrate by reactive ion etching process. Both these stampers can be made in a short processing time, and their quality is found to be higher than that of the conventional one. These stampers are transparent for ultraviolet light, so that they may also be used for making a replica disc with non-transparent substrate such as an Al substrate.
The manufacture of high performance Φ 130 mm magneto-optical (MO) discs requires the substrates with low retardation, high heat resistance and low cost in the market. The molding methods for newly compounded photo-curable acrylic resin (PHC) were studied. Thus, the pre-grooved substrate using PHC resin has been developed for the MO disc, and is capable of fast molding by a simple machine. Carrier to noise ratio (C/N) characteristics and the reliability of the MO disc with the PHC substrate are almost equal to those of glass substrate.
Eastman Kodak Company has developed an automated method of measuring double pass optical retardation. The retardation of interest is caused by cover sheet or transparent substrate birefringence of completed optical disks. The method lends itself to producing continuous curves of double pass retardation measurements at a constant radius around a disk or along a line. It is inherently insensitive to the orientation of the optical axes of the sample. The theory, equipment and capabilities will be described.
When a reflective surface is illuminated by a coherent light source, the far-field distribution of the reflected light is the Fourier transform of the surface. In this paper, we describe the far-field intensity distribution for various types of optical discs, and present some preliminary ideas for using the intensity distribution to derive information on parameters of interest. Further development of these ideas could lead to simple but powerful optical disc testers which do not need to focus and track on the disc surface.
The LH A 400 in-line sputtering system for large scale production of magneto-optical disks is described. This system is based on a modular concept to realize different layer configurations of MO-disks. The deposition stations, loading and unloading chambers are separated by dynamic buffer modules to maintain a continuous flow of disk carriers and to guarantee the stability of the sputtering processes. Transmission and reflection spectra, coercivity and MO-signal of the coated disks are measured in real-time and fed back for on-line process control. Experimental results of a process development on dielectric (A1N and Si3N4) and magneto-optical (FeTbCo) thin films in a pilot machine are presented.
Direct overwriting is studied for both magneto-optic and phase-changing optical disks. One of the most promising approaches is magnetic field modulation on a magneto-optic disk using a floating magnetic head, providing over 15 Mbps data transfer rate. Another candidate is one-laser-beam overwriting on a high-speed crystallizing material such as InSeT1Co. The present status and future possibilities of these two approaches are presented with other approaches for direct overwriting.
The pit shape in magnetic field modulation recording is obtained from temperature profile which is calculated by using three dimensional thermal diffusion equations considering the movement of laser spot. The pit edge shape changes more elliptically with increasing disk velocity. The calculated frequency response does not degrade so much as the pit edge shape changes. The influence of disk velocity to the frequency response is less than that of recorded pit duty. These calculation method is useful for obtaining the recording characteristics of read-write channel, when various parameters are changed, without experiments.
To realize high data rate and high reliability 5.25 inch Magneto-Optical(MO) disks, suitable materials for a tri-layer structure(substrate/Kerr enhancement layer/magnetic layer/protective layer) and substrates were studied. By optimizing the composition of TbFeCo film, micron-size and regular-shaped recorded domains were obtained. SiNx film showed enough Kerr rotation enhancement and good protectivity to be used as an enhancement layer and a protective layer for a TbFeCo magnetic film. Those films were constructed on newly developed plastic substrates of photocurable casting resin(PHC) which have as low retardation and as high heat-resistance as glass/2p(photo-polymerization) substrates. MO disks with the tri-layer structure on PHC showed high reliability even in severe circumstances.
A study has been conducted to determine the feasibility of a magneto-optic recording tape. Short samples of tape have been constructed and evaluated by recording and playing back signals, and by subjecting the samples to physical rigors typical of recording systems. Additionally, an experimental optical tape recorder has been constructed which achieves helical scanning of tape but which employs fixed, non-rotating optics.
Mossbauer spectroscopy has been used to analyze the magnetic and structural properties of amorphous rare earth-transition metals (RE-TM) thin films prepared under a variety of conditions. For those samples that were stable at elevated temperatures, magnetization as a function of temperatures up to the Curie point was determined.
Our recent studies of phase-change type erasable optical disk are reviewed. Two types of disk systems have been developed. The first one is a inherent overwrite system using single circular shaped laser beam. The recording materials for this case are Te-Ge-Sb ternary compositions corresponding to the stoichiometric compounds. They showed remarkable short switching time of less than 100 ns. The second type is a dual laser beam system for simultaneous erase/record in the single pass. One laser beam is circular shaped for both recording and reading. The other is elliptical shaped for erasing. The recording materials of Ge-Sb-Te-Se quaternary alloy, for this case, showed rather long erasing time about 500 ns but high sensitivity. The shape of erasing beam was modified for a successive thermal process of a homogenizing melt and a crystallizing anneal of the recording layer. The obtained erasability was less than -45dB, whilst it was about -30dB for the ordinary elongated beam by only annealing without melting.
High-density recording using a SeInSb alloy film is now possible. Recordings with mark lengths as small as 0.8-0.9 μm yield good quality signals. This medium also demonstrates good performance, as evidenced by its long-term stability and a high number of write-erase cycles. It is also clear that the avoidance of waveform distortion is essential for the high-density recording of actual signals.
The rewriteable dye-in-polymer optical media developed by OPTICAL DATA, INC. has been modeled using finite element analysis (FEA) to define the mechanisms which govern the write process. The purpose of performing modeling is to better understand the mechanisms for bump formation and erasure and to study the effects of varying material parameters. With the modeling results, it is intended that the material selection and the media structure can be optimized, resulting in media with improved read contrast, write sensitivity, mark edge definition, and cycling performance. The marks written on the media are created mechanically due to thermal expansion and material movement in the active film layers which are composed of dyed polymeric material. Because of this mechanical structure, finite element analysis provides a useful tool to gain an understanding of the bump formation and erasure mechanisms and the potential to predict changes which will enhance media performance. The value of finite element analysis modeling in helping to maximize performance has been described for hole forming media.1 Polymeric materials have nonlinear, time-dependent stress-strain curves compared to the linear curves for most metals and thus require different modeling considerations.2 Dye-in-polymer bump forming media offers many advantages which includes the performance characteristics of environmental stability, archivability, high storage density, and the ability to be erased and rewritten. Polymer films can also be applied by spin and web-coating techniques which, with low cost materials and high yields, offers manufacturing cost advantages. This paper will discuss thermal and mechanical deformation modeling results for air incident media during the write, or bump-forming, process. Included also are the principles of media operation, the role of media materials and the importance of understanding their properties.
Optical Data, Inc. (ODI) is developing a rewriteable optical storage medium which demonstrates high density read/write characteristics and exceptional environmental stability. This solvent-coated dye-polymer media, as described in the previous papers, has been demonstrated in both air incident and preformatted substrate incident forms. Both forms utilize a unique, reversible, non-vesicular, thermal-mechanical, bump-forming science to create and maintain the marks on the media. Performance data for both the air incident and substrate incident structures are presented below.
A versatile class of organic compounds has been identified as a source of potential recording layer materials for short wavelength optical data storage systems. Through modification of the structure of these materials, the strong absorption band may be tuned to any wavelength between 380 nm and 500 nm. Similar modification of other structural features permits manipulation of the physical properties without affecting the optical properties. One set of compounds tuned to 488 nm was coated onto aluminum substrates and tested in an argon ion laser drive. Tracks of pits were written in these materials at powers as low as 6-8 mW with pulse widths as low as 34 ns. Well formed pits as small as 0.4μm in diameter were observed.
Environmental test results are presented for write-once optical storage media produced by vacuum deposition of a thin film of platinum on a textured polycarbonate substrate that is produced from an interferometrically generated master. This type of storage media can be produced in large quantities using a simple production process. The disk construction is briefly described. Accelerated ageing tests were undertaken on 130mm diameter disks using high temperature and high humidity environments for both continuous and cycled conditions. The resultant changes in defect error rate, bit error rate, carrier to noise ratios and reflectivity are presented. Lifetime in a typical office environment is evaluated. This study indicates that these platinum based optical disks exhibit very long shelf and archival lifetimes and are capable of withstanding harsh environments.
We present Green's function solution of the temperature profiles induced by a moving pulsed Gaussian laser beam in optical recording thin films. Numerical results for Te and typical organic recording thin films are presented as an example of the application of the solution. The analytical solution derived in this paper is proven to be useful to elucidate the writing mechanism as well as to study the read stability.
Trilayer optical storage media with lead oxide film as spacer layer showed multiple levels of reflectance change, the reflectance change of each level are high, and write laser power for each level are ranged approximately 1 mw, indicating a potential usage of the media on multiple-valued logic storage. The recording mechanism is primarily due to lead oxide film alone from going through massicot (Pb0), minium (Pb304), complex PbOx , litharge (Pb0), massicot (Pb0) phases and melting by laser heating atdifferent power level. A direct in-contact cover glass is compatible with the recording mechanism.
The sensitivity functions (laser marking efficiency) of 10 write once read many times (WORM) optical memory media have been analyzed. All WORM media are found to fall into two classes of behavior: the first class has a behavior linear in 1/X, where X is related to the incident energy or fluence, and the second class behaves according to a Fermi-Dirac function. These expressions of the laser marking efficiency can be used to model the WORM read/write channel for all settings controlled by an optical drive.
As the title of this paper suggests, it is about CD-ROM technology and the structuring of massive databases. Even more, it is about the impact CD-ROM has had on the publication of massive amounts of information, and the unique qualities of the medium that allows for the most sophisticated computer retrieval techniques that have ever been used. I am not drawing on experience as a pedant in the educational field, but rather as a software and database designer who has worked with CD-ROM since its inception. I will be giving examples from my company's current applications, as well as discussing some of the challenges that face information publishers in the future. In particular I have a belief about what the most valuable outlet can be created using CD-ROM will be: The CD-ROM is particularly suited for the mass delivery of information systems and databases that either require or utilize a large amount of computational preprocessing to allow a real-time or interactive response to be achieved. Until the advent of CD-ROM technology this level of sophistication in publication was virtually impossible. I will further explain this later in this paper. First, I will discuss the salient features of CD-ROM that make it unique in the world of data storage for electronic publishing.
We describe a Library of Congress experimental project involving the in-house production of a digital videodisc containing digitized and compressed video still frame images from the Library's collections of prints and photographs and other sources. The medium used was a 130 mm (5 1/4 inch) write once-read many (WORM) digital optical disk with a capacity of 200 megabytes per side. This equated to about 1800 images per side. We demonstrated that component (RGB) digital encoding combined with a nominal 10 X compression yielded high quality displays which, with rare exceptions which are discussed, were indistinguishable from source video images on a conventional analog videodisc. We further demonstrated that 100 successive generations of digitized and compressed video could be produced with no discernable impairment to the image. We discuss the objectives, the experimental configuration, and applications of this system.
The data storage hierarchy of IBM System/370 compatible mainframes can be augmented by a plug-compatible optical disk storage system. The storage hierarchy consists of main memory, rotating magnetic disk memory or Direct Access Storage Devices (DASD), magnetic tapes, and hardcopy. Only data stored on DASD is available for on-line processing. Data recorded on magnetic tape is generally off-line. Long time delays are generally associated with the transfer of data from the tape library. The need exists for a form of high-capacity on-line storage. Optical storage can satisfy this need, and by emulating 3480 cartridge tape subsystems, the benefits of Write-Once-Read-Many (WORM) optical disk storage can be made conveniently available to IBM and compatible mainframes. To accomplish this, a controller is required which attaches to IBM's I/O channel and emulates a 3480 tape control unit. The resulting optical mass storage system is compatible with IBM operating systems and applications software. Data is stored on the optical disk as a collection of virtual tapes. Virtual tapes can be retrieved from a selected optical disk and, after processing, the revised data can be written to unused sectors of the optical disk. The virtual tapes save the time expended in tape mount/demount operations. The optical disk system is able to interpret and act on mount/demount messages directly, providing fully automated operation. In a jukebox configuration, thousands of virtual tapes can be handled automatically with no operator intervention. The described optical storage system addresses a longstanding requirement for on-line access to large volumes of data. By emulating the IBM 3480 magnetic tape system and storing data as virtual tapes, it offers a practical solution to the need for access to terabytes of data.
Spaceflight application of a high performance (high rate, high capacity) erasable optical disk recorder is discussed. NASA has estab-lished a program to develop an optical disk recorder focused on use aboard the unmanned polar orbiting Earth Observing System plat-forms. An expandable modular system concept is proposed consisting of multiple drive modules and a modular system controller. A drive contains two 14 inch magneto-optic disks and four electro-optic heads each con-taining a nine-diode solid state laser array (eight data tracks, one pilot track). The performance goals of the drive module are 20 gigabyte capacity, 300 megabit per second transfer rate, 10x(Exp-10) corrected BER, and 100 millisecond access time. The system goals are 120 gigabyte capacity at up to 1.8 gigabits per second rate, concurrent I/O, varying data rates, reconfigurable architecture, and 2 to 5 year operating life in orbit. The system environment and operational scenarios are presented.
A high performance Optical Disk Buffer concept for Terabit storage and Gigabit/s data rate is being developed along modular lines, such that additional new configurations for specific applications are evolving. This paper describes progress in the development of the basic modular subsystems, and correlates the modular performance with an extended family of Optical Disk Buffer configurations and system applications.
Optical Disk Memories are assessed in space radiation environments. Total dose and dose rate testing of media including Write Only Read Many (WORM) and Magneto-Optic Erasable technologies is performed and found to be hard to over 1 Mrad(Si). Optics, Optoelectrics and other critical technologies are addressed and hardening considerations presented for total dose, displacement and heavy particle radiation effects.
Supercomputer storage has been one of the limiting factors in achieving performance. Over the next decade it will become the key limitation unless the slow mass market driven evolutionary path of the storage industry is changed. Tera operation per second supercomputers of the future must have data storage and transfer systems matched to their performance.
One of the more significant recent applications of optical recording technology is the audio compact disc. This application is significant not only from the viewpoint of the audiophile, who now has available a stunning-quality audio reproduction system, but also in the eyes of the digital-data-storage world, because the CD's 72-minutes of impeccable audio resides on the disc in 600 megabytes of equally-impeccable code.