A system that directly measures errors on Compact Discs has been developed. This system will be used to study the differences in initial and time/temperature/handling-induced errors that may occur on both pressed (CD-ROM) and writable (CD-R) discs. Data reliability estimates that are independent of the CD-player used to read the discs (i.e., independent of the CIRC decoding strategy/implementation) will also be obtained.

A new optical tape recorder, based on a very fast rotating polygon is described. This system combines a high data rate with a high storage density and fast access. The recorder is compact and, apart from the polygon, requires only simple mechanics.

State of the art techniques for measuring magneto optic disks birefringence are reviewed. As an illustration of one technique, we measured the birefringence of different magneto optic disk substrates by ellipsometry. The retardation data was fitted to an analytical expression as a function of the different indices of refraction. The variation of birefringence with the depth of the substrate is suspected to affect optimum focus and track error signal. A novel scanning micropolarimeter technique for measuring the index of refraction tensor though the depth of the magneto optic substrates is presented. Modeling to study the effects of typical birefringence profiles on the performance characteristic os magneto optic disks using the data from a scanning micropolarimeter is discussed.

The status of semiconductor lasers and laser arrays suitable for optical data storage applications is reviewed. Single mode optical powers as high as 200 mW CW are available at 830 nm, while wavelengths as low as 630 nm are commercially available at CW optical powers as high as 15 mW.

Frequency doubling of semiconductor diode lasers is a potentially attractive technique for generating blue light for optical data storage applications. Here we review the status of these devices and the challenges that must be overcome before they can become practical for storage applications.

ZnMgSSe is a suitable material for the cladding layer of II-VI compound laser diodes because both the bandgap energy and the lattice constant can be controlled. Furthermore, it is found that this material has good thermal stability. Both n-type and p-type ZnMgSSe have been successfully obtained, and showed good properties for fabricating laser diodes. Utilizing this novel material, we fabricated several laser structures. Recently, room temperature continuous wave operation was achieved with ZnCdSe/ZnSe/ZnMgSSe separate-confinement-heterostructure. A review of the recent progress of blue laser diodes fabricated in our laboratory and those fabricated by other research groups is presented.

Feasibility of ultrahigh density information data storage has been newly demonstrated by using an atomic force microscope (AFM) and a scanning near-field optical microscope (SNOM). Ultrasmall gold dots about 20 to 80 nm in diameter could be stably formed on Si substrate in air by adjusting an applied pulsed voltage of AFM probe coated with gold thin film. Magnetic domains about 60 to 80 nm in diameter also could be successfully recorded on magneto optical disk material (Pt/Co multilayer) by controlling a writing pulsed laser power of sharp fiber probe with SNOM. These indicate that this technique has a potential to realize a storage density of more than 100 Gb/in² and even 1 Tb/in².

Modulation of the pit depth of an optical disk can increase its storage density. We measured a linear response to depth over the range of depth of focus using a conoscopic read head.

We have recently developed a new method of multiplexing volume holograms which we call peristrophic multiplexing. The method involves rotation the material, or equivalently, the recording beams. Peristrophic multiplexing can be combined with other multiplexing methods to increase the storage density of holographic storage systems such as holographic 3-D disks. Peristrophic multiplexing has been experimentally demonstrated using DuPont's HRF-150 photopolymer film. A total of 295 holograms were multiplexed at a single location in a 38 micrometers thick photopolymer disk by combining peristrophic multiplexing with conventional angle multiplexing. Application of this new multiplexing method toward a 3-D holographic disk is discussed.

End user applications, current storage practice, costs, device and system capacity and performance, and projected growth paths interact to shape the decisions of optical storage users. These factors indicate large scale use of CD-ROM will be followed by CD-Recordable and then mid to high performance rewritable optical storage.

The Lister Hill National Center for Biomedical Communications, a research and development division of the National Library of Medicine, is evaluating an optical disk jukebox as a digital image store to support prototype systems for image distribution over the Internet. This paper summarizes a study undertaken to determine the performance characteristics of the jukebox to support multiple image databases simultaneously accessed by multiple users. A motivation for this investigation is the need to provide users access to digitized images of medical documents and radiographs.

We have experimentally demonstrated the feasibility of a fully backward compatible erasable Compact Disc. Such discs require new phase change materials; we have identified such materials by means of novel selection criteria, finding that a range of GeTeSe alloys possess both the required recording and optical properties.

We have achieved a 2.5 inch (64 mm) quadruple density CD-ROM by developing a high resolution pick-up with our newly-developed visible laser diode whose wavelength is 635 nm, and also developing a disk cutting machine using a Kr ion laser with a wavelength of 407 nm.

We have developed Sn-Sb-Se/Sb-Bi bi-layer phase-change media for high- density write-once optical disks. Crystallized marks as small as 0.5 micrometers are stably recorded without initialization. These phase-change media, compared to ablative type write-once media, have high carrier-to- noise ratio, low jitter, and long life. Mark-edge recording with multi- pulse laser irradiation on the media provides a linear bit density of 0.48 micrometers /bit and track pitch of 1.2 micrometers using a 690-nm-wavelength laser diode and 0.55 NA objective lens. This corresponds to 1.1 Gbit/in.², or 14 GB formatted data capacity per both sides for a 12- inch-diameter disk with a zoned CAV format.

This paper reports a study of mark edge recording on the phase change rewritable disk. With the optical head using 680-nm laser diode and lens NA 0.6, 55 dB or higher carrier-to-noise ratio is obtained for signals whose recording mark length is 0.53 micrometers . In mark edge recording it is important to record all marks in their proper lengths. Hence, we first study shift behavior of the beginning and ending edges with regard to all marks, and then propose a new writing compensation method to make up for shifts. In the new compensation method the laser power modulation pattern consists of the first pulse, the multi-pulse chain and the last pulse. Adjusting the first and last pulse positions so that all marks are recorded in their proper lengths makes it possible to accomplish mark edge recording of the RLL (1,7) code with the linear density 0.4 micrometers /bit, jitter (sigma) /T(omega) to 6.5%. For the linear density of 0.35 micrometers /bit as well, a clear eye-pattern is obtained.

The mark edge recording characteristics of a new thermally balanced phase-change optical disk operating at a wavelength of 690 nm have been studied, especially from the viewpoint of designing an optical disk drive. As a recording method, the multi-pulse write compensation method with constant duration of the read power level immediately after every multi-pulse, called the off-pulse, was applied. A high carrier-to-noise ratio (CNR) of 54 dB, a high erasability of 35 dB, and an overwrite power margin from -15% to +5% were obtained for a bit length of 0.5 micrometers and a track pitch of 1.0 micrometers at 14.7 m/s linear velocity. These results mean that it is possible to design an optical disk drive providing a capacity of 1.1 GBytes using a 90 mm double-sided disk. Further, it has been found that the off-pulse plays a very important role in controlling the precision of mark edge recording.

The performances of the pregrooved Phase Change Rewritable (PCR) media have been measured by using an test drive which optical head have a 680 nm laser diode and focus lens with numerical aperture of 0.55. The write/read characteristics and groove parameters have been measured. The linear density of 1.42 Kbits/mm by using Pulse Position (PPM) recording method and track pitch of less than 1 micrometers are expected to be realized.

A rewritable digital video disc recorder, using four optical heads on both sides of a 30 cm disk which improves the data transfer rate up to 128 Mbps for phase change rewritable media, has been developed. We achieved 19 GB large capacity which realizes 20 minute Composite digital video signal recording, with new double sided multi-head MCAV method and high density mark edge recording.

This paper describes the basic principle of a new approach for large- memory optical disk storage based on the Surface-Enhanced Raman Optical Data Storage (SERODS) technology. With the SERODS technology, the molecular interactions between the optical layer molecules and the substrate are modified by the writing laser, changing their surface- enhanced Raman scattering (SERS) emitting properties, so that they are encoded to store information as bits. Since the SERS-emitting properties are extremely sensitive to molecular microenvironments (enhancement up to a million fold), lower laser energies (shorter pulses and/or faster rate) and much smaller 'molecular holes' are required for the writing process. A reading laser with much lower energy than the writing laser, and a photometric detector tuned to the frequency of the Raman emissions, are used to retrieve the stored information. The SERODS technology has great potential to offer several advantages including high storage density, unique spectral features of the encoded signals three-dimensional storage capability.

Hardware and software utilities are developed to directly monitor the Eight-to-Fourteen (EFM) demodulated data bytes at the input of a CD player's Cross-Interleaved Reed-Solomon Code (CIRC) block decoder. The hardware is capable of identifying erroneous data with single-byte resolution in the serial data stream read from a Compact Disc by a CDD 461 Philips CD-ROM drive. In addition, the system produces graphical maps that show the physical location of the measured errors on the entire disc, or via a zooming and planning feature, on user selectable local disc regions.

We suggest a simple model to quantify the crosstalks from adjacent tracks, and show some simulation results which can be used for recording density optimization. It is shown that disc parameters and optical pick-up configuration should be carefully matched with each other to achieve better performance.

It is known that significant change of birefringence accompanies field- induced antiferroelectric-to ferroelectric phase transition in antiferroelectric thin films. When an antiferroelectric lead zirconate titanate (PZT) thin film material was bounded by a semiconducting indium-tin oxide (ITO) layer, however, the phase transition was suppressed by an effect of the PZT-ITO interface. Radiation of near- ultraviolet light has shown to be effective in eliminating the interfacial suppression to the phase transition. This phenomenon has furnished a UV-activated birefringence in the PZT thin films for optical switching and storage.

A silver island film has been investigated as write-once optical storage media for commercially available 800 nm-laser diodes. The silver island film deposited at a room temperature exhibits broad resonance-type reflection characteristics in the wide wavelength regions from 430 to 850 nm due to the resonance of free electrons in silver islands. By heating the film at a temperature of >120 degree(s)C, the reflection drastically lowers in the longer wavelength region near 800 nm from the change of the resonance characteristics of the free electrons caused by the thermal deformation of the silver islands. Laser writing on the silver island films with the 820 nm-laser diode is demonstrated. In addition, it is shown that the silver island films can also be used for the shorter wavelength region of 450-500 nm since the resonance peak disappears by heating at the temperature of >500 degree(s)C from the oxidization of the silver islands.

The relationship between SNR of a differential magneto-optic signal and leaky coating reflectivity is investigated, and the condition for optimum reflectivity is determined.

Ramping protocols for polycarbonate substrate optical disc incubations are proposed which exclude conditions which could cause internal condensation or excessive sorption-gradient-induced substrate deflection.

Magnetic filed modulation recording, even at the switching frequency of 14.2 MHz, duty 33% can be achieved by the newly developed magnetic head driver.

Mass production technology of phase-change rewritable disks can be achieved by using a pass-through type in-line sputtering system. The qualities of the mass-produced PCR disk were high enough to satisfy all the specifications for this product. We optimized the composition of the recording layer (SbTeGe alloy) of the PCR disk. It was found that a Ge content of more than 20 at% in the recording layer is necessary to achieve a long archival life. The mass-produced PCR disks were very stable in the accelerated aging test. The BER stayed at nearly the same value for 2000 hrs at 90 degree(s)C, 80% RH and 4000 hrs at 80 degree(s)C, 80% RH. The life of the PCR disks was estimated to be greater than 50 years at 30 degree(s)C, 80% RH. The activation energy for the PCR disks obtained from Arrhenius plots was 1.11 eV.

We develop a readback channel model and analysis-based simulator of an optical tape system. A novel oversampled detection scheme is also described and results are presented.

For high density optical disk mastering processes, it is important to appropriately select the light source and optical layout as well as to optimize photoresist and exposure method. A g-line type photoresist is preferred for use in the mastering processes, compared with i-line type photoresist. By using the UV light source, the pit width is narrowed down to 0.25 micrometers , which is easily fabricated. Under preferred fabrication exposure power for cross talk and modulation amplitude, excellent jitter values, 8/8 ns, 10.8 ns and 16.9 ns were achieved for quadrupled, quintupled and 6-times density CD-ROMs.

The design of tracking grooves and pre-formatted data on the disk substrate is described for 2X and 4X generation optical media. A unique aspect of this study is the identification of regions in the design space of extreme parameter sensitivity. Avoiding these regions can lead to a more robust manufacturing design. In particular, for both 2X and 4X it is important to have pit widths that are a suitably small fraction of the width of the lands.

Present optical storage devices use two-dimensional recording media which do not take advantage of the ability to focus light to a small spot at a large working distance throughout the volume of a storage media. In this report we propose an approach to volumetric optical storage where the optical had reads from and writes to distinct levels of a multilevel disk structure. This approach has been successfully applied to multilevel ROM and WORM optical disk memories. We detail the physical principles behind this technology, present detailed experimental data on two-level write-once media and briefly describe four-level recording. In companion papers we describe in detail results from four-level recording and readback and multilevel ROM based media and drives.

The error rate, jitter and servo performance of a standard CD ROM drive, modified to read a disk with 2 data layers were investigated. By proper amplification of the signals to compensate for the reduced reflectivity of the data layers and by modifying the control of the drive, reading of the individual data layers was accomplished with acceptable error rates. Extension of this approach to many layers is discussed.

Waveguide electrooptic (EO) beam scanners are of interest for applications requiring high speed, high throughput, low power consumption, and modest deflection. Such devices can be used in high performance optical recording and laser printer heads. We are pursuing a novel waveguide device structure in which prisms are formed by ferroelectric domain inversion in a substrate containing a planar waveguide. The device uses TM optical modes in z-cut substrates and is therefore compatible with waveguides used for high-efficiency optical second harmonic generation (SHG).

A compact optical head module for magneto-optical disks, combining a hybrid chip integration technology and a polarizing holographic optical element, has been developed. The module size is (phi) 10 mm X t11 mm. The validity of this optical head module has been demonstrated, by successful readout operation for a magneto-optical disk.

One of the advantages of the optical head using HOE (Holographic Optical Element) is that various optical layouts and servo signal detecting schemes are available in a small package. With the flexibility in design one is able to optimize the optical system so that the tolerance in assembly becomes large. Since it is also possible to reduce the number of components, both factors contribute in reducing the cost of production. In this paper we will present a new holographic optical head with two-segmented HOE which can generate astigmatic focus error signal and push-pull radial error signal. Design process and simulation results of the focus and radial error signal will be described. The optical head was tested on a CD player and produced a good eye pattern with 3T-jitter less than 18 ns.

We propose a dual focus optical head with a holographic optical element (HOE) which compensates for spherical aberration, allowing it to read both 0.6 mm disks and 1.2 mm disks. The thin disk is read using transmitted light and the thick disk is read using +1st order diffracted light of the blazed HOE. The characteristics of the focused spot, the servo signal detection and the signal of the Compact Disc indicate that both disks can be read by the dual focus optical head.

As the demand for optical storage performance increases, the actuator designs have to accommodate the increased requirements. System tradeoffs need to be made for the various elements of the design and the best system architecture for cost and performance needs to be chosen. This article will show the consequences for the actuator designs and their relationship to the drive and media aspects.

Large capacity is a strong requirement for the next generation of magneto-optical disks in order to manage huge amount of data such as digital images. We reported that superresolution can be realized by using an exchange-coupled multilayer disk in 199 1. This novel technology is called Magnetically Induced Super Resolution (MSR) and it more than doubles the readout resolution limit of the conventional optical disk system without shortening the laser wavelength or increasing the numerical aperture (NA) of the optical lens 1),2)• The essence of MSR is that a part of the focused light spot used for readout is masked, so the effective aperture becomes much narrower than that for conventional detection. Figure 1 shows two types of detection, front aperture detection (FAD) and rear aperture detection (BAD). Since dc light is irradiated onto moving media, the medium at the rear of the light spot is much hotter. In FAD, the light spot area overlapped by the heated area is optically masked, so the signal is detected from the crescent-shaped aperture. In BAD, the crescent-shaped area is masked because the signal is erased by the initializing field prior to the readout. We would like to review some of our investigations and clarify what is important to realize an MSR system.

To reduce recording magnetic field of a magneto-optical super-resolution disk which uses an in-plane magnetization readout layer, we developed a new disk structure. By preparing a DyFeCo intermediate layer between the readout layer and the recording layer, the recording magnetic field was greatly reduced and then both super-resolution readout and mark-edge recording by a magnetic field modulation method were achieved. By using the new triple-layered disk for super-resolution readout, a carrier to noise ratio of 45 dB at a 0.4 micrometers mark length was obtained and the recording magnetic field became 15 kA/m.

Stability of magnetic domains is evaluated on TbFeCo by measuring the minimum magnetic domain width (Wmin). Domains are recorded by magnetic field modulation method. Smaller Wmin can be observed by the sample with lower Tb content and higher sputtering pressure of under-layer. This can be explained by the temperature dependency of magnetization (Ms) and coercivity (Hc) qualitatively. From these results, we conclude TbFeCo has capability to record 0.1 micrometers .

High density land/groove recording, using partial response maximum likelihood (PRML) technology, which corrects errors in the readout signal for exploiting readout channel characteristics, has been developed. By this detection method, both land area and groove area can be used for data storage tracks without a crosstalk cancellation technique. Applying this method with a red laser, 8 times the storage capacity, compared with the conventional method, has been achieved.

Bloom, the thermal expansion or contraction of the written domains in magneto-optic (MO) recording can cause degraded detection performance at high densities. To study the effect of bloom on the soft bit error rate (BER), we modeled the MO channel in the presence of bloom. Our study indicates that 4 ns of bloom causes two orders of magnitude increase in the BER when Decision Feedback Equalizer (DFE) is used with Run Length Limited (RLL) (1,7) coded Pulsed Width Modulated (PWM) signal.

Two media configurations are identified as suitable for direct overwrite, by light intensity modulation, within a fixed bit-cell encoding scheme. Unlike previously proposed media of comparable complexity, these materials do not require a second (initialization) magnet within the drive. Key to successful operation is the use of small marks and precise synchronization of old and new marks inherent within fixed bit-cell encoding. Latitudes in alignment and power for direct overwrite are assessed.

In order to use Magneto-Optical (MO) media for multi media applications, it is necessary to achieve higher density, higher data transfer rate and lower cost technologies than current MO media. MO recording is thermo- magnetic recording. MO recordings makes use of temperature modulation caused by light intensity modulation from the laser diode for recording. So, it is important to realize high speed response to the light intensity modulation for high data transfer rate recording. The high speed response is also indispensable to make small magnetic domains. So, it is important for high density recording, too. We investigate the temperature response to the light intensity modulation on MO disk. consequently, we found that MO medium shows the high speed response when the laser spot scanning velocity is large.

Optical microscopy and image processing are integrated to form a nondestructive test system for imaging magnetic domains and groove structures. High-contrast images and quantitative localized analysis such as Kerr loops, coercivity, and Kerr rotation angle can be obtained from coupons as well as from MO disks.

Electron beam radiation was used to store information into thin fluoropolymer layers. The data storage processes and mechanisms were investigated by second harmonic generation (SHG) and Fourier-Transform Infrared Spectroscopy.

A digital video disk recorder which can record noncompressed NTSC digital video signal and 4 channel digital audio signals for 32 minutes has been developed. Using (phi) 30 cm magneto-optical (MO) double-sided disk, 23 GB recording data capacity and 123 Mbps high recording bit rate were performed. In order to realize high density and large capacity recording, we have improved optical heads, recording media and others, especially we have developed the new recording method called CWL_CAV (Constant minimum Wave Length - Constant Angular Velocity.

Technologies for 32 minutes digital recording of noncompressed video and 4 channel audio signals in a 300 mm magneto-optical disk are reported.