Light path design for optical disk systems

No abstract

Reconstruction of Data from Damaged CD/DVD

Tato práce se zabývá rekonstrukcí dat z poškozených CD/DVD. Cílem práce je napsat aplikaci, která bude schopna z obrazového vstupu (naskenované fragmenty disku) získaného optickým/elektronovým mikroskopem přečíst bitový stream. Práce se také věnuje způsobu uložení dat na disku, procesu přípravy jednotlivých vzorků CD a DVD a jejich skenování. Dále je v práci popsán algoritmus vytvořeného software, jeho testování a výsledky.This bachelor thesis deals with the reconstruction of data from a damaged CD/DVD. The aim is to create an application which will be able to get a bitstream from an image (scanned fragments of a disc) acquired by an optical or electron microscope. This thesis also examines a data representation on the disc, process of preparation of specimens of CD and DVD and scanning of these specimens. The algorithm of the created software, its testing and results are described in this thesis as well.

DIGITAL WATERMARKING FOR COMPACT DISCS AND THEIR EFFECT ON THE ERROR CORRECTION SYSTEM

A new technique, based on current compact disc technology, to image the transparent surface of a compact disc, or additionally the reflective information layer, has been designed, implemented and evaluated. This technique (image capture technique) has been tested and successfully applied to the detection of mechanically introduced compact disc watermarks and biometrical information with a resolution of 1.6um x l4um. Software has been written which, when used with the image capture technique, recognises a compact disc based on its error distribution. The software detects digital watermarks which cause either laser signal distortions or decoding error events. Watermarks serve as secure media identifiers. The complete channel coding of a Compact Disc Audio system including EFM modulation, error-correction and interleaving have been implemented in software. The performance of the error correction system of the compact disc has been assessed using this simulation model. An embedded data channel holding watermark data has been investigated. The covert channel is implemented by means of the error-correction ability of the Compact Disc system and was realised by aforementioned techniques like engraving the reflective layer or the polysubstrate layer. Computer simulations show that watermarking schemes, composed of regularly distributed single errors, impose a minimum effect on the error correction system. Error rates increase by a factor of ten if regular single-symbol errors per frame are introduced - all other patterns further increase the overall error rates. Results show that background signal noise has to be reduced by a factor of 60% to account for the additional burden of this optimal watermark pattern. Two decoding strategies, usually employed in modern CD decoders, have been examined. Simulations take emulated bursty background noise as it appears in user-handled discs into account. Variations in output error rates, depending on the decoder and the type of background noise became apparant. At low error rates {r < 0.003) the output symbol error rate for a bursty background differs by 20% depending on the decoder. Differences between a typical burst error distribution caused by user-handling and a non-burst error distribution has been found to be approximately 1% with the higher performing decoder. Simulation results show that the drop of the error-correction rates due to the presence of a watermark pattern quantitatively depends on the characteristic type of the background noise. A four times smaller change to the overall error rate was observed when adding a regular watermark pattern to a characteristic background noise, as caused by user-handling, compared to a non-bursty background

Analog/RF Circuit Design Techniques for Nanometerscale IC Technologies

CMOS evolution introduces several problems in analog design. Gate-leakage mismatch exceeds conventional matching tolerances requiring active cancellation techniques or alternative architectures. One strategy to deal with the use of lower supply voltages is to operate critical parts at higher supply voltages, by exploiting combinations of thin- and thick-oxide transistors. Alternatively, low voltage circuit techniques are successfully developed. In order to benefit from nanometer scale CMOS technology, more functionality is shifted to the digital domain, including parts of the RF circuits. At the same time, analog control for digital and digital control for analog emerges to deal with current and upcoming imperfections

The Development of an Interactive Videodisc System

The thesis traces the development of interactive videodisc from origins based on early automatic machines through large-scale computer assisted learning (CAL) to microcomputer-based multi-media CAL. A comprehensive discussion of the interactive videodisc medium is provided, in terms of its features, advantages, problems, authoring and production processes, and educational applications. The requirements for interactive systems, and essential elements of video and videodisc technology are described. A relatively low-cost demonstration interactive videodisc system is developed in three phases, based on a BBC 'B' microcomputer and a Pioneer LD1100 videodisc player. In the first phase, software interfacing routines are developed in assembly language to control the player from the versatile interface adaptor (VIA) of the BBC micro. The signal control codes are based on a pulse code modulated format with uni-directional synchronous transmission. The interfacing routines are linked to, and driven by, a Basic program which provides full manual control of all player functions using the microcomputer keyboard. In the second phase, the interfacing routines are further extended to provide control linkage for interactive video application programs. Using a pilot videodisc, these Basic programs demonstrate interactive video techniques, including still frame access and the presentation of video sequences and sub-sequences. In the third phase, the application programs are converted to the authoring language, Microtext. The assembly language interfacing routines are developed into a corresponding Microtext extension command module. A mixer/genlock unit is used to provide graphics overlay of video still frames. An evaluation of the demonstration system is provided, in terms of developmental difficulties, its hardware and software features and capabilities, and its potential as a base for further suggested research work

Optical publishing

Thesis (M.S.V.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1983.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCHBibliography: leaves 46-48.by Eric Stewart Brown.M.S.V.S

Micro- and sub-microstructuring and characterisation of technical surfaces by means of laser direct writing including a novel approach for laser beam profiling

Within recent years, numerous fields of engineering, like mechanics, optics and electronics, have been influenced and revolutionised by the technique of microand nano-structuring. For example, special optical elements for beam shaping, surface structures for the reduction of friction or modern "lab on chip" devices have been produced. Within this thesis a universal system has been developed facilitating the production of such structured surfaces with dimensions down to 500 nm. This system is not only capable of structuring surfaces by means of lithographic processes; it further allows the inspection of surfaces by scanning their topography. To realise such a system, two different technologies have been evaluated: Scanning Near-field Optical Lithography (SNOL), a very sophisticated technique which uses a thin fibre tip to expose a photo resist-covered surface, and confocal scanning technology. Here, the confocal scanning is accomplished using an adapted optical component, the optical pickup unit (OPU), from a gaming console, which turned out to be the most suitable and cost-efficient solution for the realisation of this system. Several test series have been carried out during this work, to verify the performance of the confocal system, both to structure photo resist surfaces and to characterise unknown surfaces. This present work will show the ability of the developed system to produce structures down to the sub-micron range and to characterise unknown surfaces with sub- micron precision. Various patterns have been written into photo resistcoated substrates to structure their surface. Beginning with diffractive optical elements (DOE) for beam shaping, followed by Dammann gratings for twodimensional beam shaping and optical gratings for light guidance as well as producing technical surfaces imitating the properties of sharkskin or simple micromechanical structures, the developed confocal system has shown itself to be flexible and widely-applicable. IV During the development of the confocal system, a strong need for a beam profiling system analysing the light beam diverging from the OPU, was recognised. Due to the fact that no commercially available system was capable of characterising beam sizes within the range of the diffraction limit, a novel method for beam profiling was invented. This method makes use of the fibre tips already applied within the SNOL system, producing tomographical scans of the beam spot

Self-pulsation dynamics in narrow stripe semiconductor lasers

In this paper, we address the physical origin of self-pulsation in narrow stripe edge emitting semiconductor lasers. We present both experimental time-averaged polarization-resolved near-field measurements performed with a charged-coupled device camera and picosecond time resolved near-field measurements performed with a streak camera. These results demonstrate dynamic spatial-hole burning during pulse formation and evolution. We conclude from these experimental results that the dominant process which drives the self-pulsation in this type of laser diode is carrier induced effective refractive index change induced by the spatial-hole burning