Optical data storage readout with quadrant pupil detection

A novel detection scheme that uses combinations of quadrant signals derived in a pupil of the optical system is described for optical storage devices. The signals arise because of an asymmetry in the reflected light distribution when the focused spot scans data with a nonzero tracking offset. Theoretical and scalar diffraction characterization indicates that the signals may be useful for improved data density by reducing intertrack interference (cross talk). The signals may also be useful for providing a tracking error signal.     

Optical response of photopolymer materials for holographic data storage applications

We briefly review the application of photopolymer recording materials in the area of holographic data storage. In particular we discuss the recent development of the Non-local Polymerisation Driven Diffusion model. Applying this model we develop simple first-order analytic expressions describing the spatial frequency response of photopolymer materials. The assumptions made in the derivation of these formulae are described and their ranges of validity are examined. The effects of particular physical parameters of a photopolymer on the material response are discussed.     

Optical storage systems

The article describes the different types of optical storage media and their relative advantages and disadvantages. It explains how the present confusing situation, with very little standardization, has arisen and outlines the problems in achieving such standardization and the likely ways in which matters may move.     

Optical characterization of multilayer stacks used as phase-change media of optical disk data storage

We report results of measurements of the optical constants of the dielectric layer (ZnS-SiO2), reflecting layer (aluminum-chromium alloy), and phase-change layer (GeSbTe, AgInSbTe) used as the media of phase-change optical recording. The refractive index n and the absorption coefficient k of these materials vary to some extent with the film thickness and with the film deposition environment. We report the observed variations of optical constants among samples of differing structure and among samples fabricated in different laboratories.     

光存储材料及其存储机理

对卤化银胶片、全息材料、光谱烧孔材料、电子俘获材料等及其光存储机理进行了综述,介绍了清华大学光盘国家工程研究中心在基于卤化银胶片的多波长光存储等方面所做的一些工作.     

Biomolecular optical data storage and data encryption

The use of bacteriorhodopsin (BR) as an active layer in write-once-read-many optical storage is presented. This novel feature of BR materials may be used on a wide variety of substrates, among them transparent substrates but also paper and plastics. The physical basis of the recording process is polarization-sensitive two-photon absorption. As an example for this new BR application, an identification card equipped with an optical recording strip is presented, which has a capacity of about 1 MB of data. The recording density currently used is 125 kB/cm/sup 2/, which is far from the optical limits but allows operation with cheap terminals using plastic optics. In the examples given, data are stored in blocks of 10 kB each. A special optical encryption procedure allows the stored data to be protected from unauthorized reading. The molecular basis of this property is again the polarization-sensitive recording mechanism. The unique combination of optical storage, photochromism, and traceability of the BR material is combined on the single-molecule level. BR introduces a new quality of storage capability for applications with increased security and anticounterfeiting requirements.     

Optical data storage system with a planoellipsoidal solid immersion mirror illuminated directly by a point light source

A new solid immersion mirror called the planoellipsoidal (PE) solid immersion mirror (SIM) for the near-field optical storage is proposed and developed. The PE SIM has a small aperture on the apex of the ellipsoidal surface. The intensity distribution of the transmitted field is calculated by using the vector diffraction theory. Compared with a conventional solid immersion lens (SIL), the proposed PE SIM has the following features. A PE SIM replaces three optical elements of the collimator, objective, and SIL in a conventional SIL optical storage system, so that the optical system equipped with the PE SIM is not only simple in its assembly but is also effective in making an optical head unit. The PE SIM obtains light from a point light source and focuses it directly on the recording layer, which may be useful for a compact optical data storage system. The convex ellipsoidal surface of the PE SIM can reduce the risk of the SIM touching the surface of the recording medium. In addition, the spreading of the spot size with the increase of distance is very small in the PE SIM.     

Data storage in 2000-trends in data storage technologies

Recent projections by experts in computer systems and semiconductor technology indicate that in the year 2000, personal computers will have a processing speed of 100 million instructions per second and a semiconductor RAM capacity of 1 Gbyte. To work with such a system, data storage devices will need to provide more than 10 Gbytes of capacity and a data rate of 100 Mbyte/s. The advances required by magnetic and magnetooptical disk drives to meet these requirements are examined. Plausible system configurations for achieving these goals are described. A magnetic disk drive utilizing eight 3.5-in. disks on one spindle appears to be a possible configuration. Because of a larger areal density, a magnetooptical disk drive could meet the capacity requirements with only a single 3.5-in. disk. On the other hand, achieving the 100-Mbyte/s data rate and access times comparable to those of magnetic disk systems will require some technological breakthroughs. Without these breakthroughs and assuming magnetic disk progress as expected, magnetooptical disks are expected to provide many of the functions which floppy disks provide today-transfer of programs and databases between systems and economical offline storage     

Optical encryption of digital data

Smart-pixel architectures, which use the cells of field-programmable gate arrays to provide electronic functionality and intraplane communication, offer a general-purpose approach to exploiting new application areas that would benefit from this kind of structure. One such area, that of the encryption of digital data, is discussed here. Some of the characteristics exhibited by encryption algorithms and ways in which these are applicable to smart-pixel technology are described. The implementation of an algorithm in current use, the SAFER K-64, and its interfacing to an electronic host are then considered in detail. It is shown that this encryption algorithm maps well onto smart-pixel technology because it involves only parallel data transfers, simple regular operations, and interconnections plus a relatively low rate of transfer to the host.     

Optical readout for optical storage with phase jump

A novel, to our knowledge, optical readout for optical storage with phase jump is presented. In the readout scheme two coherent laser beams are focused on an optical disk with one beam scanning along pits and the other along land. When the probe beam scans across a pit, two phase jumps will take place in the interference resultant of the two beams if the phase difference between two beams is prefixed at pi, resulting in a phase pulse of 180 deg. The slopes of rising and falling edges of the phase pulse are infinite, and they are not affected by the intensity variation of the light source, stray light, and the vibration of the disk. Therefore this phase pulse can be used to read out the information on an optical disk. The use of phase jump will improve the signal-to-noise ratio of the readout signal and enhance the density of optical storage. An optical readout with phase jump was constructed. Both the theoretical design and the experimental verification are conducted. Experimental results show that the proposed optical readout is feasible.     

Nanophase change for data storage applications

Phase change materials are widely used for date storage. The most widespread and important applications are rewritable optical disc and Phase Change Random Access Memory (PCRAM), which utilizes the light and electric induced phase change respectively. For decades, miniaturization has been the major driving force to increase the density. Now the working unit area of the current data storage media is in the order of nano-scale. On the nano-scale, extreme dimensional and nano-structural constraints and the large proportion of interfaces will cause the deviation of the phase change behavior from that of bulk. Hence an in-depth understanding of nanophase change and the related issues has become more and more important. Nanophase change can be defined as: phase change at the scale within nano range of 100 nm, which is size-dependent, interface-dominated and surrounding materials related. Nanophase change can be classified into two groups, thin film related and structure related. Film thickness and clapping materials are key factors for thin film type, while structure shape, size and surrounding materials are critical parameters for structure type. In this paper, the recent development of nanophase change is reviewed, including crystallization of small element at nano size, thickness dependence of crystallization, effect of clapping layer on the phase change of phase change thin film and so on. The applications of nanophase change technology on data storage is introduced, including optical recording such as super lattice like optical disc, initialization free disc, near field, super-RENS, dual layer, multi level, probe storage, and PCRAM including, superlattice-like structure, side edge structure, and line type structure. Future key research issues of nanophase change are also discussed.     

Acrylamide-based photopolymer for microholographic data storage

The application of an acrylamide-based holographic photopolymer for bit-format holographic data storage is investigated. Holographic reflection gratings with a spatial frequency of 5640 lines/mm and micrometer radius were recorded at 532 nm wavelength using 1 μJ write energy. A diffraction efficiency of up to 0.2% was measured.     

Inorganic materials for optical data storage

Recyclable holographic (optical) storage in inorganic materials is nowadays possible due to the advent of laser. Various performance parameters of the state-of-the-art of optical storage are discussed in detail with reference to the well-established case of ferroelectric lithium niobate (LiNbO₃). Various physicochemical techniques are employed in understanding the microscopic mechanisms responsible for optical storage in LiNbO₃. A short summary of other inorganic materials capable of holographic storage is also presented.     

Modeling of multilayer microholographic data storage

We focus on the investigation of multilayer recording in microholographic data storage. We have developed a numerical model for calculating the electromagnetic scattering from thick microholographic gratings using the Born approximation and the direct volume integral. The signal-to-noise ratio and bit error rate were calculated to estimate the noise arising from interlayer and interhologram cross talk. Measurements were done to prove the validity of the model. The results of our calculations and the measurements show good agreement. We present the application of the model to the investigation of confocal filtering at the image plane and to the evaluation of positioning and wavelength tolerances.     

共焦双光头多层数据存储系统

为了实现双光子多层数据存储系统的实用化,利用现有DVD高精度聚焦、循迹伺服技术,构建了共焦双光头多层数据读写系统,实现读写焦点在三维存储材料中的精确定位.同时由D/A输出选层信号控制音圈电机,实现了层间跳转,达到了多层读写之目的.本文通过建立光学头的音圈电机模型以及音圈电机控制器模型,实现对共焦双光头多层存储系统的建模与仿真,并给出已有的实验结果.     

Microholographic multilayer optical disk data storage

Micrometer-sized reflection holograms can be written into a rapidly rotating homogeneous photopolymer disk at the focus of a high-numerical-aperture beam and its retroreflection to implement high-capacity multilayer digital data storage. This retroreflection is generated by an optical system with positive unity magnification to ensure passive alignment of the counterpropagating beam. Analysis reveals that the storage capacity and transfer rate of this bit-based holographic storage system compare favorably with traditional page-based systems but at a fraction of the system complexity and cost. The analysis is experimentally validated at 532 nm by writing and reading 12 layers of microholograms in a 125-microm photopolymer disk continuously rotating at 3600 rpm. The experimental results predict a capacity limit of 140 Gbytes in a millimeter-thick disk or over 1 Tbyte with the wavelength and numerical aperture of Blu-Ray.     

Phase-change materials for rewriteable data storage

Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.     

Security optical data storage in Fourier holograms

We have proposed and demonstrated a holographic security storage system that is implemented with a shift multiplexing technique. The security function of this storage system is achieved by using a microdiffuser (MD) for random phase encoding of the reference beams. The apparatus of random phase encoding in this system offers an additional and flexible function during the recording processes. The system can generate holographic security memory or nonsecurity holographic memory via using the MD or not. The storage capacity and the average signal-to-noise value of the security storage system are 16 bits/μm(2) and 3.5, respectively. Lateral shifting selectivity in this holographic security storage system is theoretically analyzed and experimentally investigated.