Patents, copyrights, and other intellectual property issues such as inventorship and authorship, respectively, are of great and growing concern to the technologist. Issues concerning these matters are taken up here with emphasis on an example of optical storage technology: the invention of the pulse-modulated, optical disk system. Foreign law differs in many cases from U.S. practice and will not be considered here.

Disc technology related to CD-ReWritable and recording characteristics at higher speed will be presented. Potentially for the higher density aiming at DVD-ROM capacity will be also addressed.

We review the current status of high density phase-change optical recording at red wavelengths. A user bit capacity of 3.0 GByte has been realized on a 120 mm rewritable disk by using in-groove recording and a simple and reliable wobbled groove format. The headerless format shows excellent data and address integrity during cyclability tests and it has a high degree of compatibility with read-only DVD. In order to extend disk capacity even further, both radial and tangential densities must be increased. In increasing the radial density, land/groove recording appears more promising than in-groove recording because optical cross-talk between neighboring tracks can be largely cancelled. A reduction of the track pitch in land/groove recording below 0.74 micrometers results in thermal cross-talk, leading to partial erasure of data in the adjacent tracks. The minimum bit length which gives acceptable recording tolerances in both land and groove tracks is 0.32 micrometers . With the combination of a track pitch of 0.74 micrometers and a bit length of 0.32 micrometers , an areal density of 2.7 Gbit/in² and a user capacity of 3.5 GByte should be possible in land/groove recording.

This paper describes combination of Magnetically induced Super Resolution (MSR) with Light Intensity Modulation Direct Over Write (LIMDOW) Magneto Optical (MO) media. Actually, a certain type of MSR is easily associated with the conventional LIMDOW. We combine Front Aperture Detection (FAD) MSR with the conventional LIMDOW by our mass-producing line in MNOptical. We estimate the robustness of FAD-LIMDOW by using Tagachi Method. It is confirmed that productivity and robustness of this FAD-LIMDOW is as same as that of the conventional 5X LIMDOW. The performance supports that 0.34 um/bit and 0.8 um/track pitch with NA 0.55 and 680 nm LD wave length will be practical.

A readout method to amplify the MO signal by using a magnetic domain expansion phenomenon have been proposed. It was found that the small MO signal reproduced from 0.08 micrometers crescent shaped domain was amplified 5 times larger than that of conventional disk without readout field. Also the reproduced signal level reaches to about 70% of the saturated signal amplitude. The result corresponds to 20 Gbit/in² areal density with conventional 680 nm laser.

Our measurements show that the diffraction efficiency falls off as the square of the number of holograms, and the recording order does not appear to be significant for holographic data storage in bacteriorhodopsin.

A very high density optical disk system is newly proposed. The system uses a laser diode array consisting of 100 X 100 (equals 10 thousands) VCSELs (vertical cavity surface emitting lasers) with a very small center hole on each output mirror of each cavity. Each 10 thousand laser diodes can emit evanescent wave on a surface of optical disk medium and can write information bits on it. Each 10 thousand tracks can be written and read at once, by inclining the array about 0.57 degrees toward to a tangential direction of the rotating disk. The Each track that is about 20 nm width doesn't has any borderline between tracks, which means that the total 10 thousand tracks can be traced electrically at once with 199 micron meter width. The new system enable us to write and read information as rapidly as 10 GByte/sec and to store data up to 2 Tera Bytes on one surface of 5.25' disk.

A read/write model for magneto-optic data storage is described. The model runs under the MATLAB environment on an IBM-type personal computer. Applications of the model in the areas of write compensation, for ensuring regularity in the recorded mark shape and location, and optical equalization on readout are presented.

Mutual influence on the holographic memory devices (HMD) characteristics has been considered. The possibility of their variation by the way of the controlled change of one of these characteristics, and by the way of HMD separate links parameters optimization and matching has been shown. The special attention has been payed to the optimization of parameters for such important link as acousto-optical device.

A new phase-change disk that has a double-reflective-layer structure and a recording film that contains a high-melting- point component is examined. With this medium, 10⁵ overwrites with a little mark-edge jitter in the mark-edge recording scheme and a long storage lifetime have been achieved. The beneficial effects of the double-reflective- layer structure and the high-melting-point component in reducing mark-edge jitter and their mechanisms are discussed.

A simple model to clearly show the causes of offset in DPD (Differential Phase Detection) signal is suggested. From this model, we can see the offset mechanism in case lens shift and disc tilt occur, respectively. We also suggest the feasibility of using 2-segment DPD. Comparison of 2-seg. DPD with conventional 4-seg. DPD is made.

Redundancy in modulation coding schemes for optical storage can be exploited for copy protection purposes. Two examples are given. One is a method of storing encryption key data in a manner that will not be transferred in byte by byte copying. The other makes a copy that is likely to be error prone.

The EFMPlus is the run-length-limited modulation code adopted for the DVD. Enhanced performance can be obtained by using equalizers that exploit the d equals 2 constraint of this code. Two such equalizers are presented and their performance evaluated using modeling and simulations. The use of this equalization strategy avoids the Viterbi detector, and optimal detection is provided by use of only a comparator.

The technique of pit-depth modulation is applied to optical data storage. Pits of M possible depths are written end-to- end to form a groove encoding log₂(M) bits in each mark. Data was encoded onto discs with CD dimensions using standard photoresist mastering and replication methods. Methods for removing inter-symbol interference are demonstrated on pits as short as 0.6 micrometers . A 6-level pattern of 0.6 micrometers pits was read by an optical head from a 6X CD-ROM drive and the original levels were recovered with a standard deviation of approximately 6% of the dynamic range. A system prototype read data encoded as 4-level 0.8 micrometers pits with a raw bit error rate of 3 X 10^-4.

To exceed the capacity limitation of the optical method of data storage, we record and read digital data in three dimension in photorefractive material which is photosensitive for recording and refractile in reading. Experimental results are shown with photopolymers, photorefractive ferroelectric crystals, and photochromic dyes. Thirty layers have been successfully recorded and read in 300 micrometers -thick photopolymer film. Optical systems, including a confocal laser-scanning system and a two-photon laser-scanning system, and photorefractive materials suitable for 3D data storage are discussed with current problems for commercial applications.

Three layer data recording has been demonstrated in monolithic disk media using two-photon absorption. Two dimensional data arrays have been recorded and retrieved in parallel. The recording process has been modeled and simulated. Fluorescence has been detected from a disk spinning at 1500 rpm with a signal to noise ratio of 10.

A linear optical tape recorder has been developed and its performance is evaluated. Write-once and rewritable tape samples are tested and on the basis of these results the expected performance of the recorder is concluded. In the recorder data are written and read back with the spot from a single laser that is scanned over the surface with a 10- faced polygon, rotating at up to 3500 Hz. The data density is 1.6 micrometers ²/user-bit, offering 70 Gbyte storage capacity in a VHS-C like cassette. Read and write data rates up to 4.4 and 3.2 Mbytes respectively can be achieved. A novel tape guiding systems winds the tape at a velocity exceeding 20 m/s, offering an average access-time of 1.5 s.

Optical tape offers the greatest volumetric storage density of any commercially available storage medium, and thus is a cost effective alternative to traditional forms of archival storage. Traditional optical tape mechanisms read a 1D line of data marks. We propose a 2D read-out mechanism that can improve the data transfer rate of optical tape systems to meet future demands. However, such a mechanism relies on a CCD array for retrieving an image of data bits stored on the tape. In order to recover the binary data, some processing of the image data must be performed, which should not be detrimental to the throughput of the system. We have experimented with two data recovery techniques, one based on image processing and one on an artificial neural network. We describe an experimental set up of the read-out head in our laboratory for obtaining data that are then processed by the two data recovery methods. Our results show that the neural network performs better in almost every case. The resulting RBERs indicate that with the expected improvements in the hardware of the read-out mechanism any errors in the array of bits will be corrected by the error control process.

We have realized the readout of optical disks with a 7.7 GB capacity (a track pitch of 0.58 micrometers and a minimum mark length of 0.31 micrometers ) using a ZnMgSSe laser diode and an objective lens with a numerical aperture of 0.6. We employed high-frequency modulation of 300 MHz for the ZnMgSSe laser diode drive circuit to minimize feedback noise. Measured jitter was 9.2% of a channel bit.

We consider a high power laser diode with significant external feedback from the entrance facet of a butt-coupled fiber. The effective reflectance of Fabry-Perot etalon, formed by the laser and fiber facets, undergoes deep modulation due to the change in the laser-to-fiber separation. This results in the variation of nonlinear lasing characteristics and the optical properties of the oscillation cavity, which leads to a significant wavelength tuning (up to 15 nm). The developed model successfully predicts experimental results. The longitudinal mode spectrum, tolerances and relative intensity noise are characterized as well.

Our group has investigated a number of finite conjugate aberration compensation systems in conjunction high numerical aperture objectives for multiple-layer optical data storage. The results of our investigation are that a Burch-type objective lens in conjunction with a Galilean telescope is a compact, simple and effective optical system for spherical aberration compensation.

We report certain diffraction effects that are pertinent to the operation of double-layer optical recording media. The diffraction of light from the out-of-focus layer and the resulting distribution on the in-focus layer are studied using computer simulations. The findings are then verified by direct measurements. We also describe a technique for analyzing (by computer simulation) the focus-error signa, FES, in systems that use the astigmatic method in conjunction with the double-layer disk. The results of our computer simulations of the FES are compared with those measured in an actual disk drive; good agreement between computation and measurement is obtained.

Recent results in DVD mastering using dye polymer media and direct-read-after-write technology are discussed. A comparison of this process to photoresist technology is given.

For multi-media applications, a higher density rewritable optical disk with a reduced track pitch becomes extremely important. To narrow the track pitch, increasing the groove depth of the land/groove recording type optical disk has been proposed. Not only magnetooptical recording systems but also phase-change recording systems can be applied to the deeper groove technique which gives wider recording power margin in addition to the cross-erase suppression, so that the high density rewritable optical recording systems will be steadily realized without shorter wavelength laser diodes.

Achieving disk overwrite at a high-data-rate depends on increasing both the disk revolving speed and recording bit density. This work was done to estimate the possible data transferring rates that can be expected in the near future. It is projected that combining the typical phase-change material Ge-Sb-Te and a `thermally-balanced structure' to decrease over-write distortion, several 10 Mbps will soon be obtained by a red laser and more than 100 Mbps will be obtained by a blue laser.

Recently, the magneto-optical " and the phase change materials have been competitively developed for the optical memory discs. The latter has been recognized as the promising media due to their direct overwritability and the relatively high signal-to-noise ratio. The as-deposited phase change thin films usually consist of major amorphous state and the minor crystalline state. Therefore, it needs to be uniformly crystalline state prior to creating the amorphous recording marks in the crystalline matrix. The initial complete cxystalline state is made by irradiating continuous laser beams onto the film deposited onto the rotating disk substrate. The laser-induced czystalline state depends on the power of laser source and the linear velocity of the rotating disk. For practical use, it is necessary to find out optimal laser-annealing conditions for initiallizing the as-deposited films into the complete crystalline states. In this work, the phase change GeSbTe films were heat treated with the laser beam ( A 830nm) at a variety of laser powers and linear velocities. The percentage changes in reflectivity (4R) were measured before and after laser beam irradiation on the samples to estimate the structural states of the recording layers. The lattice images of the as-deposited states, laser-induced crystallized states and subsequently recorded amorphous states were also observed with an HREM (High Resolution Electron Microscope).

Optical properties of three different phase change alloys (GeSbTe, InSbTe and AgInSbTe) are measured and compared. The experimental results are used to compute properties of multilayer stacks for phase change recording.

Although magneto-optic materials are often characterized and compared by misleading `figure of merit' (such as Kerr rotation), the Lissberger-Mansuripur figure of merit has many advantages. Using this figure of merit we can directly study, for example, the effect on the MO signal of Pb or Bi in nanolayered TbFeCo. No comparable figure of merit has been available for optimizing phase change materials in optical media. In this paper we show how the Lissberger- Mansuripur figure of merit can be extended to phase change materials, and we calculate its value for GeSbTe.

It is found that there is the region in the exit pupil of the objective lens where waveform polarity of crosstalk from adjacent tracks is inverted from that of total crosstalk. Additionally, the regions that contribute to the total signal of fine mark pattern are separated into two regions with a gap remaining along the radial direction of the disk. Shading or polarity inversion in the region neither this signal region nor inverted crosstalk region reduces the crosstalk from adjacent tracks without reducing the signal of a fine mark patterns.

A hybrid finite-difference-time-domain/angular spectrum propagation modeling technique and a finite-difference thermal model are used to study near-field optical and two- photon absorption data storage systems. The electromagnetic model is used to analyze scattering effects in structures where scalar-based theory is not appropriate. The thermal model is used in a near-field magneto optic data storage system to calculate data mark sizes.

We describe an efficient decomposition of the diffraction pattern from optical disks that yields insight into the origin and characteristics of various signals. Babinet's Principle is used to separate components that describe the data signal, servo signals, and two types of crosstalk. The construction of a basis set is described that yields efficient calculation for optimization studies. Two media types are considered as examples. Several applications are also described, including an explanation for the origin of the differential phase detection tracking signal that is used with DVD-ROM media.

Tri-layer magnetic super resolution (MSR) media was designed and fabricated for use with center aperture detection. Because short wavelength recording will be essential in achieving ultra-high density disks, the media was tested on a blue light (488 nm) magneto-optic spin stand to evaluate its MSR performance. A single layer TbFeCo disk was also prepared as a standard. Since the MSR disk forms an effective read-out aperture smaller than the diffraction limited spot size, it was observed that the tri-layer disk yielded larger carrier-to-noise ratio than the conventional TbFeCo disk for sub-micrometer mark lengths as small as 0.2 micrometers.

A new storage technique based on microscopic reflection holograms is presented. This technique has the potential to provide storage capacities of up to 100 Gbyte on a CD-like disk. The influence of wavelength- and angle multiplexing on the storage density is investigated and an estimation of the total storage capacity as a function of the focus radius is given. The major advantage of our holographic technique over other holographic storage approaches is the opportunity to achieve compatibility to existing CD and DVD systems.

A volume holographic data storage system is modeled as a digital communication system. We present two different models for the digital holographic channel. Bit Error Rate results obtained from linear equalization using these two channel models are presented.