A random-access beam scanner using axial-mode expansion of a stack of piezoelectric disks has been fabricated and tested. The measured performance was comparable to that of scanners using galvanometer or piezoelectric bimorph drivers. Computations predict that improved coupling of the stress developed by axial-mode devices can extend the performance of these devices to levels well beyond those now available.
A 180 Mega-pixel per second, optical image recording system supporting 300 line per inch resolution has been developed and is presently being tested. This paper concentrates on the electro-optic techniques utilized to produce a film image employing a laser, multiple (integrated) acousto-optic modulators and polygon raster sweep deflection.
The design of a solid-state laser beam deflector is described for applications requiring line scanning of several thousand resolvable elements. Key features of the system include an optical technique for converting a two dimensional array of pixels to a one dimensional array and a special signal format for activating the pair of acousto-optic deflectors which produce the two dimensional array.
An analog method was developed for compensating surface reflected light intensity data for predictable and unpredictable variations in incident beam intensity. The compensation is performed in real time by dividing the reflected light intensity by a reference beam intensity which is split from the incident beam. The compensated signal is then a function of surface reflectance which is insensitive to the spatially-dependent beam intensity modulations encountered with acousto-optic scanners, as well as to unexpected modulations introduced by laser instability, spatial filter vibration, and dust accumulations in the optical path. Analog circuitry, described as a "Reference Compensated Photodiode Amplifer," was developed to implement this compensation method in rapid beam scanning applications. The amplifier has a frequency response which is flat within + 0.5 db from dc to .5 MHz, and is capable of correcting the reflected light intensity data for variations in incident light intensity of over 30%. The compensation scheme and circuitry are presently employed in an optical surface flaw inspection system being developed at the Hanford Engineering Development Laboratory (HEDL).
Optical disc recorder systems are being developed for ultra-high data rate, high-density applications. These systems utilize multiple independently modulated laser beams to simultaneously record closely spaced tracks of data with near diffraction limited performance. The record and playback laser source for these systems is an argon laser whose output is efficiently split into the number of beams needed to achieve the desired data rates. Two techniques for beamsplitting were evaluated -- acousto-optic deflectors and phase gratings. The record beams are passed through a multiple transducer A-0 modulator to encode the desired information to be recorded and focused onto the optical disc to form closely spaced tracks. A second set of low-power unmodulated beams pass through the same optical system and are focused onto the optical disc to allow playback while recording for data verification purposes. These same beams are also used for normal playback during subsequent data retrieval operations. The optical designs for these systems will be described and test results presented.
RCA Corporation has been actively developing optical disc media, techniques and systems which can store 1011 bits per disc at bit error rates of 10-9 and user data rates of 100 Mb/s. In parallel with efforts to improve the media and hardware, new techniques have been developed to manage the statistically inevitable errors which will occur in the recording, storage and playback process. These techniques, which include EDAC codes, data blocking formats and data verification schemes, have been implemented in operating hardware at RCA. Error sources in Optical Disc systems are outlined and media and hardware error management techniques are described.
A ten-facet precision machined mirror with an air-bearing spinner was developed for use in laser-scanner and laser recorder systems. An interferometer, constructed to measure facet flatness, also revealed surface microstructure contributing to the mirror's noise figure. Pyramidal errors of the polygon were measured using a highly sensitive but simple optical, setup which enabled measurements to be taken in of static and dynamic modes.
In order to achieve high capacity archival optical storage, one of the key criteria is selecting a recording media which provides good writing and reading characteristics, good archival qualities and low cost. In this paper I shall describe a computer-controlled static material testing system (MTS) and samples of the test results as applied to Te-monolayer, Te-trilayer, Drexler, Thomson-CSF and the iron dispersion materials. For the recording and reading light source, an argon laser is operated at fundamental mode at X = 515 nm and is externally modulated with an acousto-optic modulator. For reading and focus-tracking, the modulator is operated at a low (-50 μW) level CW mode to provide illumination light. The modulator can also he pulsed at high power (up to 32 mW at the sample surface) with 0.8 p.m spot size at short intervals (>50 nsec) on command for recording laser pulses in coincidence with the read spot position, The focusing, readout, sample movement, laser power control. data acquisition and data analysis are all performed under mini-computer control with human intervention. Manual control mode is also provided and is very desirable for exploring new and unfamiliar materials. A video camera system provides direct viewing of the recording process. Reflectivity of the sample before (R0) and after (R1) the recording laser pulse is measured and read by the computer; from this data a modulation parameter (or contrast), (R0-Ri)/(R0 + R1), is calculated. This measurement is repeated many times to accumulate a statistically significant distribution which aives recording and material noise characteristics important for optical recording. The entire process is repeated at different recording powers to obtain recording power characteristics and sensitivity as well as different pulse widths to obtain reciprocity characteristics. Recording speed (hole opening time) can also be measured with the system. The results of these measurements will be presented for Te-monolayer, Te-trilayer, iron dispersion, Drexler, and Thomson-CSF materials.
The experimental evaluation of a photochromic material and a photodichroic material for use in wideband digital disc recording. Photochromics and photodichroics have the capability of high resolution recording at high data rates and are in addition erasable. A general description of the recording mechanisms are given, and the sensitometry, frequency response, and image stability are summarized.
The design of the two most common types of tellurium based optical data disks is discussed. A firs order merit function is defined. It is shown that a tellurium layer in the 100 to 150 A range maximizes this function in the case of a single absorbing layer on glass. If a so-called trilayer structure is used, a 20-fold improvement in the merit function can be obtained. Bit error rate is one of the most critical parameters to measure on the final product, yet there is little equipment which can handle it in a quantitative manner. In addition, storage condition standards need to be established to enable archivability to be defined and tested.
The availability of optical disk memory with archive lifetimes will require either metal films that oxidize very little, or else transparent barrier coatings that will block oxygen transport. Polymers transmit both water vapor and oxygen. Ion beam deposited Diamond-Like Carbon films are expected to provide a hermetic, oxygen barrier coating to extend the lifetime of optical disks.
This paper describes an alternative technique to laser scanning for nonimpact printing on a photosensitive medium. The laser light is formed into a line of illumination which illuminates a linear array of light modulators which in turn is imaged onto the photoreceptor. This array is implemented as a total internal reflection (TIR) spatial light modulator, with the electrodes and drive electronics fabricated on an integrated drive element which is placed against the total reflection surface of an electro-optic crystal. The localized change in index of refraction produced by the fringing field between each two electrodes is read out with Schlieren readout optics which image the TIR interface onto the photoreceptor. This paper will describe the basic device concept, present measurements on the required electrode spacing, length, and drive voltage, discuss analytically and experimentally the cacteristics of the relay imaging system, and show experimental results for modulators built with simple test electrode structures and a passively addressed full scale silicon device.
An integrated version of a total internal reflection (TIR) electrooptic spatial light modulator is described which utilizes a silicon integrated circuit as the drive electronics to address a 5376 element device. The integrated driver includes the addressing electronics, electrode drive circuitry, and electrodes, and is proximity coupled to the electrooptic crystal by pressing it against the crystal surface. The fringing fields from the electrodes on the silicon integrated circuit penetrate the electrooptic crystal, producing a line image with individually controlled intensity modulation between adjacent electrodes. This modulator, when coupled with an appropriate light source, can be used as an element for a xerographic printer or for writing on photographic film.
Many optical and electronic considerations enter into the selection of optical spot size in flying spot laser scanners of the type used in modern industrial and commerical environments. These include: the scale of the symbols to be read, optical background noise present in the symbol substrate, and factors relating to the characteristics of the signal processor. Many 'front ends' consist of a linear signal conditioner followed by nonlinear conditioning and digitizing circuitry. Although the nonlinear portions of the circuit can be difficult to characterize mathematically, it is frequently possible to at least give a minimum depth of modulation measure to yield a worst-case guarantee of adequate performance with respect to digitization accuracy. Depth of modulation actually delivered to the nonlinear circuitry will depend on scale, contrast, and noise content of the scanned symbol, as well as the characteristics of the linear conditioning circuitry (eg. transfer function and electronic noise). Time and frequency domain techniques are applied in order to estimate the effects of these factors in selecting a spot size for a given system environment. Results obtained include estimates of the effects of the linear front end transfer function on effective spot size and asymmetries which can affect digitization accuracy. Plots of convolution-computed modulation patterns and other important system properties are presented. Considerations are limited primarily to Gaussian spot profiles but also apply to more general cases. Attention is paid to realistic symbol models and to implications with respect to printing tolerances.
A strobe-recording technique is described which uses an amplitude-modulated carrier to drive an acousto-optical Bragg cell. The diffracted light is most optimally used in a loss modulation scheme for film exposure in order to maximize system efficiency. Requirements and typical performance characteristics for the Bragg cell, film, and laser are presented.
A novel interferometer is described which is capable of measuring the parallelism of two faces of the same object. The use of this interferometer to compare an angle of a scanner with the angle of a reference standard is described and the results of measurements of a state-of-the-art optical scanner are given.
The manufacture of optical scanners by the process of thin film epoxy replication is providing an attractive alternative to the conventional methods of fabrication. High quality optical surfaces achievable by replication make possible their effective utilization through the entire optical spectrum. Substrate materials can be chosen for optimum performance. A variety of optical scanners is presented which illustrate designing specifically intended for replication.
Diamond fly-cutting machines have been developed to cut specular surfaces on flat parts with a high precision, both for flatness and accurate location of related surfaces on the parts. One natural application of diamond machining is the fabrication of optical scanners. Ancillary tools and fixtures are an important consideration in this process, which with proper evaluation can favorably influence scanner cost and performance. This paper discusses typical tools and fixtures in relation to the components and machine. The ultimate payoff of careful fixture design is better performance for less money.
Several designs for anamorphic beam shaping optics will be described, applying a unique zoom lens principle based on Gaussian beam propagation. These systems were developed for use in medium resolution polygon-type scanners employing either gas or semiconductor lasers. Their primary advantage lies in the achievement of an independence of magnification parameters in orthogonal meridians within the constraints of source size variation and correction of facet pyramid errors.
A position sensing galvanometer system was designed and built using advanced techniques to provide absolute position accuracy in the order of arc minutes in the severe environment encountgred in aircraft. A particular requirement of the system was to operate a relative large mirror (6 gm-cm2) at 80 Hz with an adjustable offset of up to 6°.
A review is presented of current and expected performance of semiconductor laser diodes for use in optical printers. Improved reliability, power output, and component reproducibility for devices emitting between 700-800 nm are expected to facilitate development of printers operating with up to 100 pages per minute throughput.
As a result of extensive research and development during the last ten years, holographic optical elements (HOEs) are now considered to be practical. Key parameters and basic prop-erties of HOEs are briefly reviewed, and characteristics of various hologram types and recording materials are discussed. HOE design and fabrication approaches are also discussed.
The IBM 3687 Supermarket Scanner is designed to read the familiar UPC bar code appearing on nearly all grocery and many non-grocery items. In the past six years there have been a number of articles explaining the basic concepts involved in reading the UPC code with the scanner. The interested reader is referred to the reference articles (1, 2, 3, 4).
The original Holofacet(TM) high-performance holographic scan system is shown easily moderated in resolution and speed to match the more relaxed requirements of reprographic type image scanning and recording. As in the initial high speed tests, output scan remains normal to the rotating axis, while stability and efficiency are sustained in either reflective or transmissive modes. Options for economical replication, field flattening, multiplexing and multi-dimensional scan remain, as in the original Holofacet designs.