Multibeam acoustooptic and electrooptic modulators enable ideband laser recording and optical data processing with reduced speed mechanical scanning. This paper presents an overview of the characteristics of several types of multibeam modulators based on optical diffraction including multifrequency AO, multiport AO, and E0 modulator arrays. First, the functions of multibeam modulators in page and disc recording formats are reviewed. The characteristics of acoustooptic traveling wave modulators are discussed with particular emphasis on the modulation capabilities of multifrequency multibeam modulators in parallel and sequential operation. The alternative imaging operation mode of acoustooptic modulators is described including pulse imaging and snapshot imaging. The characteristics of multiport AO modulators with multiple rf channels are compared with those of multifrequency modulators. Finally, full line simultaneous recording techniques are considered with some comparison of recently developed electrooptic spatial light modulators and acoustooptic methods.
Application examples of multi-beam acusto-optical modulators in laser-electrophotographic printer and film plotter are given. A family of laser-graphic equipments has been built with a unique acousto-optic modulator: - high quality laser printers - high speed, high resolution film drawing machine Main advantages of multi-beam modulation: it facilitates high speed and high resolution writing and reduced mechanical complexity at the same time, the deflection system is simpler than in single-beam equipments, lower modulation frequency is required at the same writing speed. Printouts and drawings made by the equipments demonstrate our results.
In order to equip the CIT Alcatel 5520 printers, Soro has studied and conceived a laser writing sub-system. The choices Soro made in designing this optical assembly : gaz laser, multibeam acousto-optic modulator, electromechanical scanner allow to realise non impact printers able to deliver an (2I0mm x 297mm) plain paper copy at an eight dots per millimiter resolution in less than three seconds, by electrophoto-graphic process.
The design, construction and general characteristics of a triple function machine are described. The digitized raster input and output scan are produced by a polygon type flying spot laser scanner. The optical system is the underfilled, double pass type with anamorphic scan line wobble correction. In order to further enhance pixel placement accuracy, an advanced type of Polygon Signature Correction and a Motor Hunt Correction technique were developed and implemented. The scan head is built into a standard Xerox 3107 copier in such a fashion that the conventional photocopy function is retained. The coupling of the two optical systems was made possible by the inherent compactness of the scanner that permitted the sharing of the optical path. Document "reading" in the input scan mode is accomplished by a concave mirror type light collector, coupled with a small Photo Multiplier Tube.
Major holographic scanner concepts, basic design considerations and useful hologram types will be surveyed. Comparisons to other scanning techniques, as well as problems and prospects of holographic scanners will conclude this review.
Large-angle light deflection is accomplished by diffraction from an optically induced index modulation created by the interference of two controlling light beams. The control beam wavelength is used to change the frequency of the transient grating and hence the resulting deflection angle. The Bragg condition is maintained over a wide range of deflection angles by the use of a novel optical system containing diffractive elements operating in real-time to tilt the diffracting structure. The results of a computer simulation and optimization program are presented together with experimental verification demonstrating 11.8° deflection from a 0.027 μm wavelength change.
A linear spatial light modulator has been developed for laser printing. It provides capability for parallel modulation of several thousand points across a line of illumination, which is then imaged onto a photosensitive medium. The spatial light modulator, which has been described previously, utilizes a VLSI silicon chip containing addressing electronics, drive transistors, and a series of metal lines. This chip is pressed against a single crystal piece of lithium niobate, so that flinging fields created by voltage differences between metal lines are proximity coupled into the crystal and generate locally controllable changes in the index of refraction. The device is read out in total internal reflection off the proximity coupling interface, with schlieren readout imaging optics used to convert the phase modulation of the wavefront to a modulated line image. This paper will review the basic device concept, describe some of the device design and operating parameters, discuss printer application considerations, and show results from a breadboard level printer.
We describe the realization of an ultra fast deflector in Ti-diffused LiNbO3 waveguide. We realize practically in 100 ns a linear scanning of an optical beam crossing the component. A driving voltage of 35 volts gives a deflection angle of one degree and the voltage causing deflection to the first spot position (following the Rayleigh resolution criterion) is 10 volts.
The importance of Non-Impact Printer is increasing for the office of the future. Based on our experiences with electro-optical materials over several years as well as our knowledge in the field of photoreceptors we have used polycristalline ferroelectric ceramic (PLZT) and SeTe-photoreceptor as a solid state like printer version. The PLZT light gate array gives the information block-parallel to the photoreceptor. PLZT is a perovskite-type solid solution of PbTiO3 and PbZrO3 with a defined addition of lanthanum oxide. The discharging procedure is identical to the process of a copier equipment and done in accordance to the specification of the Comite Consultatif International Telegraphique et Telephonic (CCITT) for facsimile equipments Group 3.
Precision galvanometers and multifaceted polygons are produced in prototype and production quantities by the thin film epoxy replication process. These mirrors are useable over the full spectral region from ultra-violet to the visible to the long infra red. Flatness to 1/10 wave and angular accuracies to 2 arc sec are practical. Substrate materials include aluminum for minimum cost and beryllium for minimum inertia. Test results on both galvanometers and prismatic scanners are presented.
Metrology and production aspects of a precision polygon mirror bea, deflector are discussed. The Intop-Watt air bearing spindle integrates a polygon mirror wheel into a scanner drive unit of utmost compactness, without mechanical overconstraints. This unit is the ideal combination polygon/drive for applications requiring the accuracy provided by air bearing spindles. Accuracy verification for all essential functional surfaces is described based on "all-over" interferometry.
Piezoelectric Translators convert the electrical energy directly to a mechanical movement. That is the reason why piezoelectric translators have a lot of advantages if used as positioners in applications with demands of high accuracy and resolution. Possibilities and realization of new developed and optimized piezo translators for long expansion or high forces have been taken into consideration.
In some applications, such as laser printing, the scanning mirror is required to work within very severe tolerances, in order to insure good dot alignment and uniformity, which are essential conditions for high level print quality. In the present paper some methods are described, based on optoelectronic devices and a minicomputer data acquisition system, which permits measurement of the relevant parameters of the laser scanner with adequate precision.
A new Interferometer is described which is capable of measuring the parallelism and flatness of two faces of the same object. The use of this Interferometer is described and the results of measurements are given.
Centration, tilt and offset of spheric and of aspheric surfaces are detected by an interferometer with a zonal rotary scan by means of a precise air bearing spindle thus providing the topography of the sample.
Three laser scanning instruments will be described for the inspection of surfaces; particular emphasis will be put on the components to provide special optical features. The first instrument is a pinhole detector for strip materials which can also be used for surface inspection. Two independent alternate scan lines are produced to highlight holes of various angles within the strips. A large, efficient, light guide collection system collects the transmitted light, and an acousto-optic modulator reduces the laser beam power when the scan is beyond the edges of the strip. An ancillary channel of the instrument collects part of the specular light reflected from the strip surface of one of the two scans and, by means of a double reflection at the inspected surface, such effects as gross tilt and heave of the strip do not affect the inspection process. Another strip inspection instrument using two scan lines is employed to detect all classes of defect in clear strip, such as glass or plastic. The two scan lines in this case are created simultaneously and are arranged to scan, on the far side of the strip, two linear gratings which are arranged to be exactly out of phase with each other. The scan of the light transmitted by the gratings should thus normally be constant and any deviation from this indicates the presence of defects in the strip. The third instrument has been designed to inspect the internal surfaces of cylinder bores for surface defects, the position and size of ports and surface finish. Two versions will be described, one using a probe containing a single clad optical rod and a second with a more complex fibre optic assembly.
Over several hundred years of refinement, the graphic arts industry has become skilled in producing images, in the form of printed pages, that maximize both esthetics and information content. Their capabilities have grown out of centuries of trial and error. The electronic-digital automation of these basic arts and crafts is the critical path for the printing industry, and 1982 was a year of intense activity in the electronic prepress area of the graphic arts. Most current developments are directed at integrating pictures and text in final page form. This paper reviews how laser technology is being used in the graphic arts, and how effectively these products are meeting the objective of providing cost/effective solutions to traditional graphic arts production problems.
A variable format laser scanner and plotter has been developed for the graphic arts and other industries. By using a galvanometer to move the laser beam, the scan amplitude can be adjusted so that only the area of interest is scanned and digitized. Compared to other scanning methods (e.g., spinning polygon and rotating drum), this leads to efficient use of memory, drastically reduced data rates, and increased resolution at high magnification. The machine is capable of scanning a 20 in. by 24 in. area at 1500 lines per inch in four minutes. Optical encoders are employed on both scan axes to insure geometric accuracy. The system is microprocessor controlled with the operator interface through a CRT, keyboard, and menu type software. Scanning and plotting are done in daylight with automatic roll film loading and processing.
Industrial application of Lasers in the graphic industry is undoubtedly increasing. Examples are typesetting, colour separation and laser dot generating, laser printing, laser gravure, laser plate making, etc. Application of laser technology in the area of security printers had a rather slow start but is speeding up rapidly. Encoding credit cards by laser and holography are examples of the application of lasers in this field. In this paper we shall shortly summarize the known industrial applications of lasers in the graphic industries and report about the applications of lasers in the detection of a coded watermark. A step and repeat holographic laser camera for the production of holograms in dichromatic gelatine will be described.
A raster scanning laser pattern generation system for imaging printed circuit board (PCB) master artwork has been developed. The system can generate a master artwork image up to 600 mm (fast scanning direction) by 650 mm (slow scanning direction) in size at a 370 cm2/min. imaging speed, guaranteeing ±20 pm feature location accuracy in the whole imaging area. Introduction of this system to the master artwork imaging process is expected to result in a dramatic effect realizing an imaging time reduction by a factor of ten on the average and by a factor of more than thirty on large scale and high circuit density master artwork, even when time for data handling is taken into account.
Design of a scanned laser display system is described. The equipment presents a full-colour large screen TV display of 525 and 625 line standard using off-air or recorded video signals. It has two lasers as light sources, an Argon laser providing green and blue primary colours, and a dye laser pumped by excess power from the Argon laser, providing the red primary. The design stresses efficiency in the use of laser power to achieve a bright image. The advantages of scanned laser display systems, including inherently good colour and resolution, are discussed in compari-son with light valves and CRT-based displays. Present and future applications of laser displays are noted.
This paper describes the design of a system that scans an array of GaAs laser beams over a thermally-addressed smectic liquid crystal cell. The cell is projected onto a 1 m square screen to create a very-high-resolution storage display (8000x8000 pels). The scanning system chosen to achieve this high resolution image uses optical fibers to couple the output of 32 GaAs lasers into a two-column array. The array is imaged onto the LC cell by a small plastic lens which, along with the fiber array, is scanned over the area of the cell by a linear X-Y mechanism. The performance and limitations of this addressing method will be discussed and compared with those of alternate multi-beam systems.
Scanning techniques in optical microscopy up to now were employed in the rather limited field of microscope photometry. The use of lasers as a light source offers new possibilities because of the high intensity and good collimation of the laser beam. Modern electronic and scanning techniques make - in addition to the photometric possibilities - the build-up of high quality microscopic images possible.
Holographic optical elements or systems of holographic elements may replace glass optical imaging systems or may be used for the correction of glass optics. The main advantages of such systems are their low weight, small and compact construction, and their simple and inexpensive manufacture. The disadvantages to be overcome are mainly the low light through-put and chromatic aberrations. In the special case of optics for video discs we present an optical imaging system which is capable of giving the required high resolution for illumination with polychromatic radiation of limited bandwidth in the case of semiconductor laser diodes. Optimization programs based on ray tracing yield highly corrected imaging systems by comparably simple holographic means. The use of only two surfaces gives very compact and lightweight systems, the image quality of which is described for monochromatic and polychro-matic irradiance by means of optical transfer functions. The holograms are recorded on photo-resist material with short wavelength laser radiation. Such holograms have almost no scatter light and do not alter their properties with time or under radiation. These holograms generate wavefronts for the correction of aberrations which, in the case of glass optics, could only be achieved by aspherical surfaces.
We report on high density recording experiments of digital information in Te alloys on pregrooved discs. The recording and reading of information is done on a recorder fitted with an AlGaAs laser. We describe experiments with modulation systems using pit-length modulation based on runlength-limited codes. Runlength-limited sequences were adopted as a modulator output because of the fact that this class of restricted sequences has a great impact in magnetic and optical recording. State-of-the-art high power solid-state lasers can emit a light pulse of sufficient energy for only a limited time and can therefore only be used in a pulsed mode. Pit-length modulation is achieved by adjusting the rotational velocity of the disc and laser pulse write frequency in such a way that oblong pits of overlapping monoholes result. We demonstrate the feasibility of recording densities of up to 1 Mbit/mm2 with the application of pit-length modulation schemes.
Semiconductor lasers are used to an increasing extent in electro-optical systems. The highly divergent emission of the laser is usually collimated into a parallel beam. The properties of the collimated beam are directly related to the properties of emission. The physical origin of far-field distribution, wave aberration, astigmatism and polarization are discussed and related to the properties of the collimated beam. Refractive-index guided and gain-guided lasers are compared with regard to maximum output power, coupling efficiency, wave aberrations, and feedback-induced noise.
A high resolution laser scanner or recorder, used in the printing industry, will address a large number of pixels on a page, typically 108 - 101° pixels. The data rate will generally be about 10 Mbit/s. Processing, transmitting and storing such quantities of data gives emphasis on data compression techniques. Further, in many instances the compacted data can be more conveniently processed than the original pixel or run length format data. An example of this is the scaling of outline coded fonts and logotypes, and gray level coded photographs. We discuss in this paper the requirements imposed on codes useful in compacting laser scanned images. Primary features of interest are: compression ratio and its dependence on the type of image, processing capacity and speed required in coding and decoding, possibility of processing the coded data, and effects on the quality of the image. Some further points concern noise reduction, unfaithful coding techniques, origin of the coded images, and merging of data of different code structure. The problems created by the lack of standardization of graphics industry image coding are commented on and a comparison is made to telefacsimile codes. The coding problem is also addressed from the point of view of the extensive research carried out in the fields of image processing and image analysis. The research in high resolution image coding is seen to be at an early stage compared to the level of research in the fields of coding of television pictures, photograph images or low resolution facsimile.
In rotating polygon line scanners for non-impact printing on a moving photoreceptor, placement accuracy of the image data on the photoreceptor is a key determinant of print quality. This is achieved through the use of a PEL (picture element) clocking signal operating at a frequency equal to the number of "dots" to be written per second. By controlling both phase and frequency of this PEL clock, compensation can be made for several systemic characteristics that would otherwise produce image data distortion. Some of the principal contributors to such distortion are:
1. Variations in spinner motor speed.
2. Asynchronous relationship between scan rate and PEL clock.
3. Variation in photoreceptor speed.
4. Non-linearity of the optical scan system.
Although it is possible to design and build opto-mechanical systems in which photoreceptor feed rate and scan velocity are made linear and stable, it is more economical to use the system electronics to make the image data rate (PEL clock) accommodate the system characteristics. Photoreceptor feed rate variations alter the image aspect ratio and are typically very low frequency changes (<.05 Hz). These can be corrected by "slaving" the spinner motor speed to the photoreceptor feed rate. The spinner motor itself has speed variations (typically <2 Hz) which in turn, can be corrected by "slaving" the PEL clock to spinner motor speed. None of these variations or corrections produce any appreciable scan velocity change within a single scan. This paper will describe techniques in which electronics is used to control both the frequency and the phase of the PEL clock to correct for all of these dynamic characteristics to produce fixed spatial frequency on the photoreceptor in both scan and feed directions. Optical distortion or scan system geometry may produce variations in spot velocity within the scan line. This static distortion is identical in each sweep and is not affected by the factors discussed in this paper.
A conventional intra-cavity Pockels cell was used to achieve tunable operation of a Rh 6G dye laser. Wavelength tuning over a broad spectral band (500 PO with driving voltages of some hundreds volts was achieved. This system is suitable for simulating broadband illumination in optical processors working with spatially coherent but temporally incoherent sources. Applications dealing with the measurement of optical path-differences through the channelled spectrum technique, surface testing by chromatic speckle phenomenon and optical transmission by spectral modulation of light are reported.