Diode laser are often used as light sources for transmitting information through optical fibers. One of its inherent property is the astigmatism, due to this fact an anamorphic system is required to perform couplings between this kind of lasers and fibers. In this work a theoretical study of the propagation of elliptical gaussian beams emitted from the diode laser through anamorphic gradient index lenses is presented, as well as the way of correcting the astigmatism.
Design considerations and fabrication method of an all-solid-state five layer electrochromic (EC) system are discussed. A dry method of lithiation of the system is proposed and characterized completely for its use in the fabrication of EC systems. Some preliminary data on the EC switching of the complete system are presented.
The simulation of the read/write (R/W) process for optical disk and drive is useful in several aspects: It provides insight understanding of component performance for component or subsysteTa designer, and it helps the system designer to evaluate the system performance and making system specification at the early stage of the development program and before system integration [1-11].
Most operating systems have no fail-safe features built into their file systems. They rely on recovery programs to repair the file systems after failures have occurred. These actions often result in loss of files, and sometimes the files are not recoverable. The loss of data in high capacity storage devices is extremely costly. We illustrate how robust file systems may be built for the WORM optical disks.
A fast access, three beam swing arm optical reading head is proposed for the a half height CD-ROM disk drive. The swing arm is designed to achieve an access time in the 20 msec region for a comparable performance with the Winchester disk drive. The angular orientation of the grating is being controlled so that the three beam tracking method can still be used for the circular path of the swing.
The use of Optical Data Transfer Systems (ODTS) is an established fact in the field of telecommunication, but still no break-through has taken place for the implementation in next generation Parallel Computers. High speed serial data transfer systems, carried out with singular components for both the transmitting (Electro-Optic Transducers: EOTs) and the receiving (Opto-Electric Transducers: OETs) side, already serve the telecommunication sector for a long time. A Laser as an EOT, a monomode glass fiber as a transmission medium and a PIN photodiode as an OET pretty soon allow a data throughput rate of several TerraHz. Parallel Processing however imply a simultaneous transfer and storage of a large number of computer words, of which the width can vary from 64 bits till a multiple (''W'') of it. A number of problems announce themselves if an attempt is made to combine the two in principal different technologies of data transport. Moving a parallel computer word through a serial data link at a constant throughput rate of ''T'' word/sec, coerce the processing rate at electrical side to increase with a factor ''W''. The transfer rate ''W*T'' is essential to execute the parallel (''W'') to serial and serial to parallel conversion. The assembly of the bulk of EOT and OET components, the drain away of the heat dissipation and the verification of the increasing influence of EMI and crosstalk, in case ultra wide band signals are used, are tedious attendant problems. Implementing fibers only do not guarantee a solution in case the data has to be distributed over a large amount of parallel channels. Piled flat-cable like fiber bundles in combination with free space distributing techniques offer a solution in most cases. Integrating a new class of Opto-Electric Logic Elements in an ODTS enables an optical parallel transfer and storage of data; in this way improving the parallelism in next generation computers.
Computer-controlled electrically addressed SLMs can be used as scanning elements in programmable holographic scanners. This new kind of scanners could realized high-speed scanning with predetermined locus because of the real-time computer generated holograms displayed on the SLMs. The performance of the programmable scanner is mainly limited by the parameters of the SLMs.
We describe novel electron trapping (ET) materials for an erasable 3D stacked layer optical memory. ET materials can store 2D optical information carried by blue light. The optical memory can be recalled by using IR stimulation as a 2D emission pattern of orange to red light. A stack of ET layers thus form a 3D stacked layer memory.
The final step of many picture storage applications is an image display to be viewed by a human observer. It is therefore worthwhile to take into account the basic properties of the visual system in order to develop efficient and economical solutions for picture storage. This paper gives an overview of such characteristics of the visual perception process which are relevant for image coding and display. The visual system is considered as an image analyzer comprising an optical part (the eye) and neuronal image processing stages (retina and brain). Based on results from psychophysics and neurophysiology, some perceptual effects of visual image processing are demonstrated and the spatial filtering characteristics of human vision are examined.
It is of paramount importance that a test cost reduction strategy is incorporated in the design for testability philosophy of an IC. The reliance of the traditional s fault model is inadequate in such a strategy. All studies agree that this model does not reflect the physical failures of real devices, principally because such failures do not exhibit a 1:1 mapping onto the logic domain. The author(s) have proposed the adoption of a non-tactile intelligent novel method which processes information obtained from a scanning laser beam reflected from a surface profile, such that shorts and opens in both metallic and non- metallic domains can be detected, located, and logged where necessary. Scanning may be of a raster nature over the surface, or follow a suitable path search along layouts. The latter search type has been simulated in PROLOG using breadth-first (BRFS), Euler (ES), and neighbor-first (NFS) searches. It is suggested that by creating and modifying an acquired-knowledge database (AKDB), according to defect occurrence, it is also possible to search those regions where defects may be present in order of decreasing probability, according to a prediction database (PDB). Thus a useful library of the distribution of defect density statistics should be created by virtue of this proposal. In this paper results of search simulations and discussion of the AKDB implications are included. The paper concludes that within limits, the Euler search is superior. Such a topological approach to the testing problem offers a test structure for exploitation which is technology independent, relatively fast, adaptable to parallel processing, and may be interfaced with machine vision systems.
Optical data storage has spurred the market for document imaging systems. These systems are increasingly being used to electronically manage the processing, storage and retrieval of documents. Applications range from straightforward archives to sophisticated workflow management systems. The technology is developing rapidly and within a few years optical imaging facilities will be incorporated in most of the office information systems. This paper gives an overview of the status of the market, the applications and the trends of optical imaging systems.
Single stripe gain-guided semiconductor lasers are generally fabricated with a stripe width limited to about 3 micrometers to obtain single lateral mode operation. For lasers with larger stripe widths, the carriers under the stripe induce index antiguiding that leads to near field instability. To improve on the stability of the near field, a number of quasi-index structures have been introduced such as the rib waveguide, ridge waveguide and the channeled substrate planar striped that make use of the evanescent field coupling to induce an effective lateral index step over the striped region. Quasi-index structures control only the optical field and for stripe widths larger than 5 micrometers , control of the carrier distribution becomes important as the optical field depletes the carriers leading to an inhomogeneous distribution that aids multi- lateral mode excitation. This paper presents a V-grooved stripe contact structure that preferentially channels the carrier to the center of the stripe as well as maintaining a stable carrier distribution induced by the V-groove contact. Such a laser has been successfully fabricated by liquid phase epitaxy and is able to emit in a single lateral mode with a FWHP of 20 micrometers at up to two times threshold current. The GaAlAs laser typically has an active layer of 0.1 micrometers , cladding layer thicknesses of 3 micrometers and a p-GaAs cap layer, 6 micrometers thick, with a flat-bottom V-groove etched into it. Power output of 20 mW is measured for this prototype.
A new approach to rewritable optical data storage is under development which has the potential for satisfying all of the key requirements for a dynamic on-line data storage system including removability, high data density, high speed and long cycle life. The storage media consists of alkaline earth crystals doped with rare-earth elements. Thin crystalline films of these media deposited on disk substrates can store information in the form of trapped electrons. The information is written, read, and erased entirely by optical signals in this purely electronic process. Electrons are raised to a higher energy state by the absorption of visible light photons, filling available trap sites. An electron in the elevated energy state can be released from its trap site by imputing sufficient energy to the electron to permit it to escape from the well. When this occurs, the electron falls back to its ground state and emits a corresponding photon, indicating the existence of a binary ''1'' at the storage location site. The basic advantages of the ET media arise from the physical process which is purely photoelectronic. Read and write data transfer rates are very high because the process in the ET media is electronic rather than thermal in nature. The writing sensitivity of ET is approximately 100 times better than other optical media. This implies that the data recording rate can be made 10 times higher while using only 1/10 of the optical power of other systems. In addition, thermal cycling performance degradation is not a factor in contrast to the heat induced changes wrought by the write/erase laser beam in other optical storage media.
A three beam CD optical pickup has been developed with a holographic optical element (HOE). The HOE has a hologram for beam splitting and servo signal generation on one side of a glass substrate, and a grating for tracking-beam generation on the other side. The hologram pattern is divided into two regions. The grating periods of these regions are different from each other, so that the focus error signal is detected by Foucault knife-edge method. And also the radial error signal is detected by the twin-spot method. The HOE is cemented at the top of a package in which a laser diode and a photodiode for signal detection are mounted. The HOE offers a improvement of environmental stability of the pickup too. In spite of the usage of a plastic housing, the optical pickup shows superior characteristics of environmental stability.
Wavelength division multiplexing (WDM) is a technique that enables several light sources operating at different wavelengths to simultaneously transmit through a single medium and has been widely used in fiber optics industry [1,21. One can apply the WDM technique to read several tracks of an optical disc in parallel so as to increase the data transfer rate. In section 2, the operating principles and associated design parameters of the WDM optical readout system are examined. The properties of laser diodes (LDs) that limit the number of wavelength channels to be multiplexed are the spectral spread of the diodes and -peak emission wavelength deviations. These factors affect the minimum channel spacing. The insertion loss and the adjacent channel crosstalk of the wavelength demultiplexer (DEMUX) in the WDM readout system are needed to be minimized. Dependence of both parameters on the spectral spread of the light sources and channel spacing are addressed in section 2.
The vast possibilities of optical data processing can not be fully realized due to the absence of function transformation methods of optical signal. One of the principal elements of such transformation is the on-line optical storage device. A large number of studies has been presently carried out on creation of memory elements based on electro- optical crystals. All crystals can be divided into two large groups: the first group includes crystals in which electrical information is recorded and the reading is carried out by optical means; the second group includes crystals in which two-dimensional optical signals are stored. The different physical nature of optical memory in these two crystal groups results in certain limitations of its realization in practical devices and, therefore, of its application field. Duration of information storage under conditions of optical memory realization sufficiently depends on the nature of electro-optical effect. Depending on the crystal being used the optical memory may vary from 10-10s (semiconductors) to infinite storage time (ferroelectrics), i.e. these crystals possess both operative and fixed storage.
Logic Array Structures (LAS) represent a class of sub-systems used in VLSI design. The principal reasons for the deployment of this class in design are their regularity of structure, ease of automation and verification. In addition, the mapping of 2-level Boolean functions is relatively easy to implement. Such an array structure consists of an AND-array/OR-array combination which represents the sum of products of the required Boolean function. The principal inherent disadvantages are the limitations of switching speed and fabrication area. Such advantages would be obviated by the use of optical couplers (Fig. 1) and waveguides, in which speeds would be increased by at least three orders of magnitude. Also the trends in the fabrication of optical waveguides indicate that a substantial saving in area is possible. 2The orthogonal nature of both LAS and OLAS implies that these waveguides would exhibit low loss factors.3 , This paper presents the theory of OLAS together with possible implementations. Discussion of future implications are included.
The utility of the compact disk to store data and images is almost unparalleled, yet to date little has been achieved in the market place. This paper first reviews the basics of CD-ROM (the data equivalent of CD audio technology), outlines the varieties of CD disks in development, and reviews the standards. Then from the analysis of the device a set of advantages and disadvantages are derived that apply to laser optical storage of digital data in particular in CD formats. A set of application ground rules follows with some typical examples of good and bad applications. Finally the future is examined as it relates to new evolving optical disk trends and how they could impact CD formats and applications.