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called the hologram, which may be defined as the recorded interference of two or more coherent wavefronts. When the hologram is illuminated by one of the original wavefronts used to form it, the remaining wavefronts are reconstructed . . . Observation of these reconstructed wavefronts is nearly equivalent to observing the objects from which they were originally derived." (Collier, 1966, p. 67).

"An optical hologram is a two-dimensional photographic plate which preserves information about the wavefront of coherent light which is diffracted from an object and is incident upon the plate. A properly illuminated hologram yields a threedimensional wavefront identical to that from the original object, and thus the observed image is an exact reconstruction of the object. The observed image has all of the usual optical properties associated with real three-dimensional objects; e.g., parallax and perspective." (Lesem et al., 1967, p. 41).

6.60 "Holography is the science of producing images by wavefront reconstruction. In general no lenses are involved. The reconstructed image may be either magnified or demagnified compared to the object. Three-dimensional objects can be reconstructed as three-dimensional images." (Armstrong, 1965, p. 171).

6.61 "Are Holograms Already Outdated? Holography is one of the most exciting developments of today's technology. Holograms make use of a high-energy laser beam to store or display threedimensional images for such applications as readonly storage; packing densities and device speeds are extremely impressive. However, at today's pace of innovation, holography may be outmoded before it approaches being practical. One of the latest competitors for 3-D display, storage, and wave conversion applications is the kinoform, a new wavefront reconstruction device which also projects a 3-D image, but requires one-fourth of the computer time to generate and creates images roughly three times as bright.

"A computer program is used to produce a coded description of light being scattered from a particular object. The resultant computations are used to produce a 32-grey-level plot which is photoreduced and bleached. Then, when subjected to even a very small light source, such as the girl's earring in the photo above, the 3-D image is formed. A kinoform image can be produced of any object which can be computer-described. Examples might include proposed buildings, auto designs, relief maps, or two-dimensional alphanumeric data." (Datamation 15, No. 5, 131 (May 1969)).

6.62 "The kinoform is a new, computer-generated, wavefront reconstruction device which, like the hologram, provides the display of a threedimensional image. In contrast, however, the illuminated kinoform yields a single diffraction. order and, ideally, all the incident light is used to reconstruct this one image. Similarly, all the

spatial frequency content or bandwidth of the device is available for the single image. Computationally, kinoform construction is faster than hologram construction because reference beam and image separation calculations are unnecessary. "A kinoform operates only on the phase of an incident wave, being based on the assumption that only the phase information in a scattered wavefront is required for the construction of an image of the scattering object. The amplitude of the wavefront in the kinoform plane is assumed constant. The kinoform may therefore be thought of as a complex lens which transforms the known. wavefront incident on it into the wavefront needed to form the desired image. Although it was first conceived as an optical focusing element, the kinoform can be used as a focusing element for any physical waveform, e.g., ultrasound or microwaves." (Lesem et al., 1969, p. 150).

6.63 "A new hologram made at Bell Telephone Laboratories now allows the viewer to see a 3D image rotate through a full 360 degrees as he moves his head from side to side . . . To make a flat hologram with a 360-degree view, vertical strips of the photographic plate are exposed sequentially from left to right across the plate. A narrow slit in a mask in front of the plate allows only one strip to be exposed at a time, each strip becoming a complete hologram of one view of the object.' (Data Proc. Mag. 10, No. 4, 16 (Apr. 1968)).

6.64 "Holography provides an alternative description of pictures, which might be more amenable to bandwidth compression. To investigate this possibility, it is desirable to measure various statistics of the hologram, and to try various operations on it to see what their effects would be on the reconstructed pictures. . . . Holography and other coherent optical processing . . . techniques have made possible relatively simple ways of obtaining the Fourier transforms of two-dimensional functions and operating on them in the frequency domain." (Quarterly Progress Report No. 81, Research Laboratory for Electronics, M.I.T., 199 (1966)).

6.65 "Gabor and others have proposed the use of the wavefront reconstruction method to produce a highly magnified image, using either a change in wavelength between recording of the hologram and its reconstruction, or by using diverging light for one or both steps of the process. The two-beam process is readily amenable to such magnification . . ." (Leith et al., 1965, p. 155).

6.66 "Color reconstructions should be attainable from black and white holograms if suitable temporal coherence conditions are ensured." (Stroke, 1965, p. 60).

"Holography is another field for which the laser has opened many possibilities. Perhaps it will find useful applications in pattern recognition and in storage of three-dimensional information as a Fourier transform. . .

"Three-dimensional displays of airfield approaches in the cockpit of a jet liner with the correct viewing angle from the position of the aircraft would be a more interesting application [of laserholographic recordings]." (Bloembergen, 1967, p. 86).

"We read about images having three-dimensional properties, magnification obtained by reconstructing with a wavelength greater than that used in forming the hologram, diffuse holograms which, even when broken, produce whole images, multicolor images obtaining from emulsions which normally produce only black and whites." (Collier, 1966, p. 67).

"The recording of surface deformations in engineering components demonstrated here shows how these techniques may be applied at low cost and in a short time. For teaching purposes it has been shown that interference holography of the distortions of a rajor blade can be demonstrated adequately to a large group of people in only a few minutes." (Bennett and Gates, 1969, p. 1235).

"With practical applications for holograms still in the few-and-far-between stage, the Office of Naval Research and IBM believe they have a holographic application that is both practical and unique: in a head-up, all-weather landing system.

"The system - now at the laboratory model stage-employs a hologram of an aircraft carrier. The hologram is picked up by an infrared vidicon and projected on a crt cockpit display . .

"The achievement is one of application in which a two-dimensional representation with the socalled six degrees of freedom encountered in a carrier landing, and full ranging capability, is produced without employing a computer. The demonstration model simulates an approach window two miles wide and a half-mile high and offers a 3.5-degree glide slope. The six degrees (glide-slope deviation, localized deviation, depression angle, bearing angle, roll, and slant angle) are achieved mechanically, electronically, and optically. For example, roll is achieved as the vidicon itself is rolled; glide-slope deviation is simulated by manipulating the hologram. In the model, the generated image allows a view which includes magnification of the holographic image of the carrier up to 16-to-1 and permits views including one below the deck of the carrier." (Electronics 42, No. 13, 46 (June 23, 1969).)

"General Electric has also examined the hologram for potential in character recognition. One method suggested by GE is to create a spatial filter using a hologram. This filter can be used to detect, or recognize, specific shapes from among a random


"This general scheme is the basis for a personnel identification system being developed by National Cash Register Co., Dayton, Ohio.

"According to NCR, two of the most important aspects of identification are signatures and photo

graphs. In the NCR system, a hologram containing signatures and numbers randomly located is placed in the optical path of a laser.

"If matching occurs when a signature card is inserted into a receiving device, the system locates the picture [which] is projected for comparison.' (Serchuk, 1967, p. 34).

6.67 "The wavefront reconstruction method offers the possibility of extending the highly developed imagery methods of visible-light optics to regions of the electromagnetic spectrum where high-quality imagery has not yet been achieved . . . (Leith et al., 1965, p. 157).

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6.68 "A Megabit digital memory using an array of holograms has been investigated by Bell Laboratory scientists. The memory is semipermanent, with information being stored in the form of an array of holograms, each hologram containing a page of information. A page is read . . . by deflecting a laser beam to the desired element of the array, so as to obtain reconstruction of the image stored in the element-the digital information on a read-out plane which is common to all elements of the array. Photosensitive semiconductors arrayed on the read-out plane then sense the stored information . .

"In the Bell Labs experimental system, the light source is a continuous-wave helium-neon laser operating in the lowest order transverse mode. Two-dimensional deflection is accomplished by cascaded water-cell deflectors, using Bragg diffraction from ultrasonic waves in water, and capable of deflecting the beam to any of 300 addresses in less than 15μsec...

"The present system comprises 6 k bits per page, and a 16×16 matrix of pages, for a total capacity of 1.5 M bits access time is 20 μsec. Total optical insertion loss is 75 db, resulting in 70 k photons impinging on each bit detector. . . and Bell Labs scientists project that, by straightforward extensions of the present system, 25 M bits with an access time of 7 μsec is a feasible system. This system would have 65 × 65 matrix of 6 k bit pages, a faster deflection system, and a reduced insertion loss of 65 db, resulting in 0.5 M photons per bit at the detectors.

"Ultimately, it is predicted that a memory can be built having greater than 100 million bits of storage, with an access time in the one microsecond range." (Modern Data Systems 1, No. 2, 66 (Apr. 1968).)

"Bell Labs has already constructed a 'breadboard' hologram memory system. . . that may eventually be able to display any one of 100 million units of information upon one millionth of a second's notice.

"It is based on using a number of closely spaced holograms on a single photographic plate. Bell Labs had in mind switching operations as one fundamental application . . .

"This memory system works by directing a laser


beam to one 'page' (location of a hologram) in an array. Initial goals are to make each hologram about a millimeter in diameter and to space them rather closely in a pattern of 100 rows by 100 rows. Each hologram will store, encoded in the form of an interference pattern, another 100 by 100 matrix. This will be coded in dots or blanks to represent information. The reconstructed hologram will be aligned precisely with an array of phototransistors (also under development at Bell Labs), which will 'report' to the electronic device which of the dots are present and which are absent. This roll call is the message. ." (Photo Methods for Industry 12, No. 3, 61-62 (Mar. 1969)).

6.69 "Carson Laboratories,

Bristol, Conn., for example is working on the development of potassium bromide and similar crystals as holographic materials.

"The laser is used to bleach the crystal in accordance with the holographic interference patterns. Such a memory device is said to have a capacity of 1 million bits per square half-inch of material." (Serchuk, 1967, p. 34).

6.70 "An experimental optical memory system that could lead to computer storage devices a thousand times faster than today's disk and drum storage units was reported . . . by three International Business Machines Corporation engineers.

"In the experimental system, blocks of information are accessed by a laser beam in just tenmillionths of a second. More than 100 million bits of computer information could be stored on a nine square inch holographic plate. . .

"The experimental memory system uses a laser beam to project blocks of information contained on the hologram onto a light-sensitive detector. The detector then converts the projected hologram into electronic signals which can be processed by a computer.

"In a feasibility model, assembled at IBM's Poughkeepsie, N.Y., Systems Development Division Laboratory, size, direction, and focus of the laser beam are determined by a series of lenses. The beam is positioned on the hologram by a crystal digital light deflector. By controlling the polarization of the light from the laser the deflector is used to select any block of information stored on a single plate.

"The hologram splits the laser beam into two separate rays: one non-functional and the other a first-order diffraction pattern which carries the holographic information. This first-order diffraction pattern is then focused on a light-sensitive detector array, which converts the optical information to electronic signals. The signals, representing data, are then sent to the computer's central processing unit at high speeds." (bema News Bull. 5, Nov. 18, 1968).

6.71 "An advantage of storing information in the form of a hologram rather than as a single real image is that the loss of data due to dust and film defects is minimized, since a single bit is

stored not on a microscopic spot on the film but as part of an optical interference pattern which is contained in the entire hologram." (Modern Data Systems 1, No. 2, 66 (Apr. 1968).)

"A bad spot in a photographic image will not spoil all bits of information completely; the Fourier transform of such a plate will still give a good image." (Bloembergen, 1967, p. 86).

"Since information from any one bit of the object is spread out over the whole hologram, it is stored there in a redundant form, and scratches or tears of the hologram make only a minor deterioration in the overall reconstructed image. In particular, no single bit is greatly marred by such damage to the hologram." (Smith, 1966, p. 1298).

"Leith reports that diffused illumination holograms have an immunity to dust and scratches and that particles have little effect in producing erroneous signals as in previous photographic memories." (Chapman and Fisher, 1967, p. 372).

"Since light from the point source is spread over the entire hologram's surface (thus ensuring interference patterns over the entire film surface), any part of the hologram will reproduce the same image as any other part of the hologram. It can be seen that the only effect of dust and scratches is to reduce the active area of the hologram." (Vilkomerson et al., 1968, p. 1199).

"Generally, the light projected into an image by a hologram is not associated with any specific point of the hologram, thus, if the hologram becomes marred by dust or scratches there is little degradation of any one point in the image. Dust and film imperfections can be a severe problem in nonholographic storage, because errors arise from the degradation of specific bits." (Gamblin, 1968, pp. 1-2).

6.72 Further, "the results of this study have indicated that holographic techniques are particularly suited to satisfy the functional requirements of read-only memory . . . Holography offers solutions to two key problems associated with the requirement for a single removable media storing up to 160,000 bits. First, the unique redundance inherent in holograms constructed with diffused illumination eliminates the loss of data due to such environmental effects as dust and scratches. Second, the potential freedom from registration effects which can be achieved by proper selection of construction techniques allows the manual insertion and removal of media with high bit packing densities and does not add a requirement for complicated mechanical positioning or complex electrical interconnection in the read unit." (Chapman and Fisher, 1967, p. 379).

6.73 "One can construct computer techniques which would take an acoustic hologram (the wavefront from a scattered sound wave) and transform it into an optical hologram, thereby allowing us to construct the three-dimensional image of the scatterer of the sound waves." (Lesem et al., 1967, p. 41).

6.74 "In a paper presented at the International Symposium on Modern Optics, researchers at the IBM Scientific Centre at Houston, Texas, described how they have programmed a computeran IBM System/360 Model 50-to calculate the interference patterns that would be created if light waves were actually reflected from a real object. Neither the real object nor actual light waves are required to produce holograms with the computer technique. While the initial IBM computer hologram experiments have been restricted to two-dimensional objects for research simplicity, the authors said further work is expected to make possible digital holograms which can be reconconstructed into 3-D pictures. An engineer could then get a 3-D view of a bridge or car body design without actually building the physical object or even drawing it by hand." (The Computer Bull. 11, No. 2, 159 (Sept. 1967)).

"More recently, firms have experimented with computer-generated holograms for unique data display. NASA's Electronics Research Center in Boston, Mass., is said to be investigating making real-time holograms for such applications as airport display to approaching aircraft.

"A team at IBM's Houston Scientific Research Center has programmed a System/360 Model 50 to create hologram by calculating the necessary interference patterns.

"Thus it may soon be possible to use the computer to create a mathematical model of a device and then translate equations into a three-dimensional hologram of the mathematical model." (Serchuk, 1967, p. 34).

6.75 "Holograms of three dimensional images have been constructed with a computer and reconstructed optically. Digital holograms have been generated by simulating, with a computer, the wave fronts emanating from optical elements, taking into account their geometrical relationship. We have studied in particular the effects of various types of diffuse illumination. Economical calculations of high resolution images have been accomplished using the fast finite Fourier transform algorithm to evaluate the integrals in Kirchoff diffraction theory. We have obtained high resolution three dimensional images with all the holographic properties such as parallax, perspective and redundancy." (Hirsh et al., 1968, abstract, p. H 104). "Kinoforms serve for all of the applications of computer-generated holograms, e.g., three-dimensional display, wave conversion, read-only storage, etc. However, kinoforms give a more practical, computationally faster display construction that yields more economical use of the reconstructing energy and that yields only the desired image.

"The principal computational advantage of kinoforms as compared with digital holograms is embodied in the fact that all of the spatial frequency content of the device is used in the formation of the real image; none is required for the separation of the real and conjugate images. There is then at

least a factor of four reduction in the computer time needed to calculate the wavefront pattern necessary for equivalent image quality. Correspondingly there is a reduction in plotting time for the kinoform.

"A further economy is achieved in that no calculations involving a reference beam are necessary. Finally, in the cases of one- and two-dimensional objects only real-number additions are required, once the basic transform is calculated, to determine the wavefront phase for plotting. The corresponding quantity to be plotted for digital holograms is the wavefront intensity which requires multiplication of complex numbers." (Lesem et al., 1969, p. 155). 6.76 “A[n] . . . important reason for synthesizing holograms is to create optical wavefronts from objects that do not physically exist. A need to form such a wavefront from a numerically described object occurs whenever the results of a threedimensional investigation, for example, the analysis of an x-ray diffractogram must be displayed in three dimensions." (Brown and Lohmann, 1969, p. 160).

"Scientists, stock brokers, architects, statisticians and many others who use computers may soon have a practical, fast, and inexpensive way of converting memory data into three-dimensional pictures and graphs.

"With a process devised at Bell Telephone Laboratories, it takes only a few seconds of computer time to turn equations, formulas, statistical data and other information into a form suitable for the making of holograms. Viewed under ordinary light, the holograms produce three-dimensional pictures that can display a full 360-degree view of the object shown.

"Holography, which has been called 'lensless photography,' records a subject through the interference of two laser beams on a photographic plate. One beam is aimed directly at the plate, and the other reaches the plate after being transmitted through, or reflected by, the subject being 'photographed.

"In the BTL method, the original subject exists only as a group of numbers or coordinate points in three dimensions, for example, in the computer's memory. The hologram is made in two steps. First, the computer is programmed to construct a series of two-dimensional pictures, or projections, each showing the 3-D data from a precisely defined unique angle. A microfilm plotter, connected to the computer, produces a microfilm frame for each picture.

"In the second step, a holographic transparency is made. The frames of the microfilm are used as subjects to make very small holograms (1 to 3 mm across), which are positioned sequentially on holographic medium.'

"Thus, a composite hologram is made up of a series of small holograms, each of which is formed with a two-dimensional image. But the composite image appears three-dimensional, and shows a

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360-degree view of the object. With this type of hologram also invented at BTL-the viewer can see the object rotating through a full cycle by simply moving his head from side to side in front of the hologram." (Computer Design 8, No. 6, 28 (June 1969).)

6.77 "By the use of photographic recording techniques a very high information density can be achieved to which rapid random access can be made by appropriate electronic and optical techniques. If, therefore, there are any classes of information which must be read frequently, but are not changed for at least a week, then such a storage technique would be appropriate. This is evidently the case for all system programmes including compilers and monitor programs . . ." (Scarrott, 1965, p. 141). "Photographic media are quite inexpensive, are capable of extremely high bit densities, and exhibit an inherent write-once, read-only storage capability. The optical read-out techniques, which are used, are nondestructive." (Chapman and Fisher, 1967, p. 372).

6.78 "To get an order of magnitude idea of the memory capacity, we will consider a memory plane of 2 in. square . . There will be approximately 645 subarrays [individually accessible]. Consider that only one-half the memory plane is composed of active film. The memory would then contain almost 13 million bits." (Reich and Dorion, 1965, p. 579).

6.79 "The inherent power of optical processing can be exploited without suffering the speed limitations usually associated with static spatial filters. The method consists of using an electron beamaddressed electro-optic light valve (EOLV) as the spatial filter. Thus the filter need no longer be a fixed transparency, but can instead be a dynamic device whose orientation is controlled electronically rather than mechanically. This opens the method of optical processing to the domain of real time and presents exciting possibilities for its use in a variety of applications." (Wieder et al., 1969, p. 169). 6.80 "In optical transmission lines, the wavelength of the signals will be shorter than any of the circuit dimensions; therefore, one could eliminate, for example, all the reactive effects in the interconnections." (Reimann, 1965, p. 247).

"High-speed electronic computer circuitry is becoming interconnection limited. The reactance associated with the mounting and interconnections of the devices, rather than the response of the active components, is becoming the main factor limiting the speed of operation of the circuits.

"A possible approach to computer development that might circumvent interconnection limitations is the use of optical digital devices rather than electronic devices as active components." (Reimann, 1965, p. 247).

"One factor of growing significance, as circuit size is reduced, is the increasing amount of surface area consumed by areas devoted to interconnections and pads for interconnections. There have been

marginal improvements over the past few years, but no startling improvements have been made in comparison to reductions in the basic device geometry.

"The consumption of real estate may be reduced by interconnecting the logic circuits with the narrow lines allowed by the masking technology, thus reducing to a minimum the area requirements for external lead pads. At this point, the semiconductor manufacturer relaxes and says in effect to the computer designer: Reduce your logic to a few standard configurations, and I will reduce costs by a large factor. Hence, we have a search for magic standard logic functions." (Howe, 1965, p. 507).

"Interconnections are already our problem for designing and building systems, and applying Large Scale Integration (LSI) to digital systems will inevitably force the realization that interconnections will be more important in determining performance than all other hardware factors. This is because the problems of physical size and bulk, DC Shift over long cables, reflections and stub lengths, crosstalk and RFI, and skin effect degradation are making computer systems interconnection limited." (Shah and Konnerth, 1968, p. 1).

6.81 "One example of these more exploratory attempts is the optically addressed memory with microsecond nondestructive read cycle and much longer write cycles. Chang, Dillon and Gianola propose such a changeable memory employing gadolinium iron garnets as storing elements." (Kohn, 1965, p. 133).

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6.82 "Maintaining low power supply and distribution impedances in the presence of nanosecond noise pulses is an increasingly difficult problem . . . As more circuits are placed on a chip, decoupling of power supply noise will be required on or in close proximity to the chip." (Henle and Hill, 1966, p. 1858).

6.83 "Integrated circuitry has been widely held to be the most significant advance in computer technology since the development of the transistor in the mid-fifties . . . Semiconductor integrated circuits are microminiature circuits with the active and passive microcomponents on or in active substrate terminals. In thin-film integrated circuitry, terminals, interconnections, resistors and capacitors are formed by depositing a thin film of various materials on an insulating substrate. Microsize active components are then inserted separately to complete the circuit. Micromodules are tiny ceramic wafers made from semiconductive and insulative materials. These then function either as transistors, resistors, capacitors, or other basic components." ("The Impact . . .", 1965, p. 9).

6.84 "Integrated circuit technology will bring revolutionary changes in the size, cost, and reliability of logical components. Lesser improvements will be realized in circuit speed.

"Advances in integrated circuit logic components

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