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6.1.2. Photochromic Media and Techniques




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and at RCA,6.23 an IBM system designed for and now in operation at the Army Electronics Command as well as IBM developments in variable frequency lasers, 6.24 and a recording system from Kodak that uses fine-grained photographic media, diffraction grating patterns, and laser light sources. 6.25 Holographic techniques may also be applied to the development of associative memories with possible analogies to human memory-recall systems.6.2

Kump and Chang (1966) describe a thermostrictive recording mechanism effected on uniaxial Permalloy films by the application of a local stress induced by either a laser or an electron beam, promising large capacity memories of better than 106 bits per square inch storage efficiency.6.27 Then there are combined optical and film techniques for digital as well as image or analog recording and storage. Specific examples include IBM photo-chip developments, 6.28 thermal recording developments at the NCR research laboratories,6.29 Precision Instrument's UNICON System,6.30 and, in general, the area of photochromic storage technology. Areas of continuing R & D concern with respect

laser communications possibilities include questions of modulation and transmission,6 acquisition and tracking problems,6.32 isolation from atmospheric interferrence conditions, and possibilities for controlled atmosphere systems.6.34

Vollmer (1967) notes that an experimental shortrange laser communication system has narrow beam width with significant advantages for privacy, In particular, “operation at 9020 Å enhances this privacy by virtue of its invisibility.” (p. 67.) Some examples of the experimental use of lasers for communications purposes were given in an earlier report in this series,6

6.35 and it was noted that the most successful ventures to date have been at opposite ends of the distance spectrum.6.36 However, laser scanning techniques combined with other means of communication may offer important gains in high-resolution facsimile transmission. For example, a system developed by CBS Laboratories uses a laser beam to scan photographic film, convert to video signals, and transmit, via satellite, military reconnaissance pictures from Viet Nam to Washington.6.37

Continuing requirements for further developments in the application of lasers in display systems involve, for example, efforts directed toward less expensive high quality semiconductor lasers 6.38 and toward solving problems of deflection, modulation, and focusing.6.39 Kesselman suggests that results to date in terms of laser displays are inconclusive and that practical applications are not likely in the near future (1967, p. 167). As in the case of laser versus electron beam display,6.40 the absence of requirements for vacuum techniques favors the eventual use of laser rather than electron beam techniques in many high density data storage recording applications.6.41

By definition, photochromic (or phototropic) compounds exhibit reversible effects or color changes, resulting from exposure to radiant energy in the visible or near visible portions of the spec. trum.6.42 Such media give excellent resolution and reduction characteristics, and because of the reversibility property, they can theoretically be erased and rewritten repeatedly,6.43 although a continuing area of R & D concern is that of problems of fatigue.6.44 They also enable storage of images with a wide range of gray scale.6.45 Such materials have been known for at least a hundred years or more (Smith, 1966). In fact, as Smith suggests, they may have provided the means for achieving the world's first “wrist-watch.” 6.46

Tauber and Myers (1962) and Hanlon et al. (1965) offer summaries of NCR efforts to provide commercial applicability to photochromic recording techniques for large-capacity micro-image storage files.6.47 A British example of application is the Technical Information on Microfilm Service.6.48

A less favorable characteristic of the photochromic material appears in the case of storage files - the permanency of recording depends on ambient temperature, ranging from only a few

at normal room temperatures to perhaps several years under rigid temperature controls.6.49 Therefore, for mass and archival storage, the NCR system involves transfer from the photochromic images to a high-resolution photographic emulsion for permanent files.6.50 The remaining advantages are two-fold. First, the reduction is impressive: 1,400 pages of the text of the Bible on an approximately 2" x 2" film chip is the widely demonstrated example (Fig. 2). Secondly, 'spot? erasure and rewriting provides an important in. spection and error correction capability. It is claimed that: “Instantaneous imagery followed by immediate inspection permits the production of essentially 'errorless' masters for the first time". (Hanlon et al., 1965, p. 10).

In the area of internal memory and switching design, Reich and Dorion (1965) report of the photochromic techniques that: “The photochromic medium has extremely large storage capacity latently available in physically small dimensions. The basic photochromic switches are the molecules themselves Photochromic media can be employed for many write-erase-rewrite cycles and give almost nondestructive read ... Appropriate photochromic systems can retain stored data without power consumption : The memory can probably be designed to be stored for quite a long time." (p. 572) 6.51

A photochromic medium in the form of transparent silicate glass containing silver halide particles has been suggested for such applications as erasable memories, displays for air traffic control operations, and optical transmission systems. 6.52

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In addition, it is to be noted that photochromic needs for truly long-range R & D planning in many films may be activated by CRT phosphors for use in areas of computer and information sciences and information display systems (Dorion et al., 1966)6.53 technology, since it is by no means a recent area of and may also be used for real-time target tracking.6.54 investigation, the principles having been announced Recent developments suggest the use of photo- by Gabor as early as 1948.6.57 The basic holographic chromics for digital data storage.6.55

phenomena are described by Cutrona (1965, p. 89) Finally, the properties of photochromic materials as follows: “A hologram is produced by recording on might be used for improved performance of holo- photographic film the interference pattern resulting graphic recording, reconstruction and display from the illumination of some object with a wavesystems.6.56 Thus, “the use of self-developing photo- front from the same source”.6.58 chromic devices in the place of the photographic plate would enhance the value of wavefront recon

Leith et al. (1965, p. 151) point out further that

"by combining conventional wavefront reconstrucstruction microscope by permitting nearly real-time operation and eliminating the chemical develop.

tion techniques with interferometry, it has been ment process." (Leith et al., 1965, p. 156).

possible to produce holograms from which high

quality reconstructions can be obtained. These 6.1.3. Holographic Techniques

reconstructions bear close likeness to the original

object, complete with three-dimensional characHolography is a new information processing teristics ... The object can be a transparency, or technique, but it is, in fact, highly illustrative of it can be a solid, three-dimensional object". 6.59



Electronics Command, Fort Monmouth. In particular, “it is intended that a hologram of a binary data array would constitute the card-like removable media. Upon insertion into the memory read unit, the hologram would continuously focus a real image on the data onto a photodetector matrix. Such an arrangement can permit electronic random access to the information within the array while eliminating the stringent optical requirements on the detectors involved.” (Chapman and Fisher, 1967, p. 372).6.72 Other R & D possibilities of interest include experimentation with acoustic 6.73 and computer-generated holograms.6.74 The computer generation of holographic or kinoform recordings is thus another development in this area of advanced technology. For example, digital holograms may be generated by computer simulation of wave fronts that would emanate from particular optical elements arranged in specific geometrical relationships (Hirsch et al., 1968).6.75 An interesting area of investigation is that of computer synthesis of holograms of three-dimensional objects which do not, in fact, physically


6.1.4. Other Optoelectronic Considerations

Armstrong (1965) emphasizes that, in general, no lenses are required and the reconstructed image can be magnified or demagnified as desired.6.60

As of early 1969, however, the question has been raised that holograms may be already outdated.6.61 A new wavefront reconstruction device - the kinoform-is a computer-generated device intended to provide a reconstructed three-dimensional image of various objects with greater efficiency than is available with holographic procedures (Lesem et al., 1969).6.62

In addition to the use of holographic techniques for three-dimensional image storage and recall (including rotation 6.63), these techniques are also being explored for bandwidth compression in pictorial data storage 6.64 the production of highly magnified images, 6.65 and other novel applications.6.66 In particular, it has been claimed that holographic techniques offer a new potential for high-quality-image capture in regions of the electromagnetic spectrum extending beyond those that have been achieved by optical recording techniques in the the region of visible light.6.67

Then it has been reported that “General Electric's Advanced Development Laboratories, Schenectady, build a laser holograph reader-a device capable of reading characters in several ways. It can detect a single object out of many without scanning, or if scanning is used, can recognize up to 100 different characters. The holographic reader is said to show wide tolerance for variations in type font and is expected to find applications in the computer field.” (Veaner, 1966, p. 208.)

Laser and holographic techniques in combination are also being investigated for high density digital data storage, for example, at the Bell Telephone Laboratories,6.68 at Carson Laboratories, 6.69 and at IBM.6.70

Some special areas where advanced optoelectronic techniques and improved materials or storage media continue to be needed include "certain operations, such as two-dimensional spatial filtering (that) can be readily accomplished, in principle, with coherent light optics. Problems under consideration include: the effect of film-grain noise on the performance of a coherent optical system; the relation of film thickness and exposure; techniques for the making of spatial filters; and the effect on the reconstructed picture of various operations (such as sampling, quantization, noise addition) upon the hologram. (Quarterly Progress Report No. 80, Research Laboratory for Electronics, M.I.T., 221 (1966).)

McCamy (1967) reports recent extension of previous R & D investigations into fading and aging blemishes in conventional microforms to the effect of formation of such blemishes on information stored by means of holograms. It is to be noted further that certain types of holograms have an important immunity to dust and scratches.6.71

Possibilities for a holographic read-only store are under investigation at IBM (Gamblin, 1968), RCA (Viklomerson et al., 1968), and at the U.S. Army

In general, it is emphasized that increasing interest has been evident in the use of optoelectronic techniques for both computer and memory design for a wide variety of reasons. Scarrott (1965) and Chapman and Fisher (1967) point to the high densities achievable with photographic

with photographic media.6.77 Reich and Dorion (1965) suggests a photochromic film memory plane, 2" x 2", with 645 subarrays individually accessible and a total capacity, assuming only 50 percent utilization of the film area, of better than 12 million bits.6.78 Potentially, then, many of these techniques promise significant advances in data storage, in logic and processing circuitry, in alternative communications means, in computing or access speed, and in data collection with respect to two- and three-dimensional object representation, including spatial filtering. 6.79

Bonin and Baird (1965, p. 100) list other applications of optoelectronic techniques for tape and card readers, position indicators, and recognition equipment. In addition, important new areas will include use in communication and transmission systems. Here it is noted that optical techniques as applied to advanced communication systems planning relate also to continuing theoretical investigations. Thus, “preliminary studies of communication systems employing optical frequencies have indicated three topics to which the concepts and techniques of modern communication theory may most profitably by addressed. They are (i) the import of quantum electrodynamics for the characteristics of efficient communication systems, (ii) the relevant description of device noise as it affects the performance of communication systems, and (iii) the statistical characterization of the atmosphere as a propagation channel at optical frequencies." (Quarterly Progress

Report No. 80, Research Laboratory for Electronics, overcome present-day deficiencies of processing M.I.T. 178 (1966).)

systems in such applications as pattern recogniFor use as computer logical elements, somewhat

tion.6.87 less attention has been paid to date to the opto- In terms of relatively recent R & D literature, electronic techniques. However, Ring et al. (1965,

Minnick (1967) provides a review of microcellular p. 33) point out that “it well may be that optical

research, with emphasis upon techniques useful devices which do not appear at all suitable as binary

for batch-fabricated circuit design; Bilous et al. computer elements may be very effective computing

(1966) discuss IBM developments of large scale devices in the context of some other logic structure

integration techniques to form monolithic circuit (e.g., majority logic, multivalued logics)."

arrays, where on only nine chips it was possible to Reimann adds: "With the advent of the laser,

replicate a specific System/360 computer model, efficient light-emitting diodes, and high-speed

and, under RĀDC auspices, Savitt et al. (1967) have photodetectors, interest in the application of higher

explored both language development and advanced speed opto-electronic circuits to digital logic has

machine organization concepts in terms of large increased. ... We may in the future expect to scale integration (LSI) fabrication techniques. 6.88 see opto-electronic circuits which will combine

That is, in general, where integrated circuits based laser amplifiers with other high-speed semicon

on etched circuit board techniques had replaced ductor devices." (1965, p. 248).

discrete components, the LSI techniques of fabriThen we note that optoelectronic techniques may cation produce sheets of integrated logic compoalso be used to attack some of the problems that

nents as units.6.89 increasingly plague the circuit designer.6.80 Possi

To what extent do integrated fabrication techbilities for circumventing interconnection limitations which become more severe as physical area per

niques hold promise for future developments in

very large yet inexpensive memories? Rajchman component is reduced are also stressed by Reimann

suggests that "the dominance of non-integrated (1965, p. 247). He states: "The possibility of signal

memories is likely to be finally broken or at least connection between parts of the system without

seriously challenged by integrated memories, of electrical or actual physical contacts are very which the laminated-ferrite-diode and the superattractive for integrated circuit techniques. With conductive-thin-sheet-cryotron memories are promoptical signals, a totally new approach to the inter

ising examples.” (Rajchman, 1965, p. 128.) And, connection of digital devices is possible.”

further, that "it appears certain that energetic Optoelectronic techniques as applied to the prob- efforts will continue to be devoted towards intelems of large, inexpensive memories are not only

grated technologies for larger and less costly promising as such,6.81 they also may be used to

memories, as this is still the single most important attack the noise problems still posed by integrated

hardware improvement possible in the computer circuits.6.82 Thus Merryman savs “one attractive

art.” (Rajchman, 1965, p. 128.) Other advocates property of optoelectronic devices is their potential

include Gross 6.90 Hudson 6.91 Van Dam and for isolation; they can get rid of the noise that is

Michener,6.92 Pyke, 6. and Conway and generated when two subsystems are coupled. The

Spandorfer.6.94 noise problem is even tougher in integrated circuit

Hobbs says of silicon-on-sapphire circuits that systems, because the transformers used in tradi

their fabrication is suitable for large arrays and that tional methods of isolation are too bulky.” (1965, they are indeed "promising, but presently being p. 52).

pursued by only one company." (1966, p. 38.) Of

active thin-film circuits, he concludes: "Potentially 6.2. Batch Fabrication and Integrated

cheaper and easier to fabricate very large arrays. Circuits

Feasibility is not proven and utilization much further

away.” (Hobbs, 1966, p. 38.) The same reviewer In very recent years, it has been claimed that continues: "Costs are expected to range between 3 integrated circuitry is the most significant advance and 5 cents per circuit in large interconnected in computer hardware technology since the introduc- circuit arrays . . . However, the ability to achieve tion of the transistor; 6.83 that it will bring important these costs is dependent upon the use of large interchanges in the size, cost, reliability and speed of connected arrays of circuits and, hence, upon the system design components 6.84 and that advanced ,

computer industry's ability to develop logical design high-speed techniques paradoxically also indicate and machine organization techniques permitting eventual lower costs.6.85

and utilizing such arrays.” (Hobbs, 1966, p. 39.) Many potential advantages of increased usage of Continuing R & D problems in terms of LSI LSI techniques are cited in the literature. These technology include those of packaging design,6.95 include, for example, applications in improved error detection and correction with respect to central processor unit speed or capacity perform- malfunctioning components; 6.96 the proper balance ance, in system control and reliability, and in to be achieved between flexibility, redundancy, and content-addressable (associative) memory construc- maintenance or monitoring procedures, and ques. tion and operation.6.86 Wilkes suggests that parallel- tions of segmentation or differentiation of functional ism achieved by use of these techniques may logic types.6.97 One example of many special prob


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lems is reported by Kohn as follows: "In all batch storage and recall concern first of all the problems fabricated memories, the problem of unrepairable of “main memory” – that is, the preloaded, imelement failures is predominant . . . It is an open mediately accessible, information-recording space question how complex and expensive the additional allocated at any one time to necessary system electronic circuits will be, which will disconnect the supervision and control, to user(s) programs and defective elements and connect the spare ones. data, and to temporary work space requirements. (Kohn, 1965, p. 132.) On the other hand, special It is to be noted that “this ‘main' memory size is advantages of LSI techniques for self-diagnosis and related to the processing rate; the faster the arithself-repair have been claimed.6.98

metic and logic units, the faster and larger the memory must be to keep the machine busy, or to enable

it to solve problems without waiting for data." 6.3. Advanced Data Storage Developments (Hoagland, 1965, p. 53).

Further, “this incompatibility between logic and In the area of advanced hardware, the prospects for much larger, much faster, and more versatile

memory speeds has led to increased parallel opera

tion in processors and more complex instructions as storage systems must of course be a major R & D

an attempt to increase overall system capability." consideration. Current technological advances indi

(Pyke, 1967, p. 161). cate the desirability of increasing use of integrated construction methods using ferrite aperture plates,

As of current technology, main memories are still

usually magnetic core, with typical capacities of a thin films, laminated-diode combinations, field-effect

million bits and cycle times of about one microtransistors, and superconductive thin film systems,

second.6.100 One relatively recent exception is the among other recent developments.6.99 For another

NCR Rod Memory Computer, which is claimed to example, possible applications of echo resonance

have “about the fastest main memory cycle time of techniques for microwave pulse delay lines that would be suitable for high-speed memories are being

any commercial computer yet delivered - 800

nanoseconds.” (Data Processing Mag. 7, No. 11, explored at the Lockheed Palo Alto Research Labor

12 (Nov. 1965).) This is a thin-film memory, conatory. (Kaplan and Kooi, 1966).

structed from beryllion-copper wires plated with Advanced hardware developments for improved

magnetic coating.6.101 data storage emphasize both higher speeds of access

Petschauer lists the following trends which may and readout and larger capacities at higher densities

be expected in magnetic memory developments in of storage. There are the small capacity, ultra-high

the near future: speed, memories of the read-only, scratchpad, and associative type. These typically supplement signifi

“1. Trend toward simple cell structures - 2 or 3 cantly larger capacity and slower speed "main

wire arrays. memories”. Next, there are continuing prospects

“2. More automated assembly and conductor for high density, very large capacity stores.

termination or batch-fabricated arrays. There is finally the question of R & D require

"3. More fully automated plane testing. ments in the area where the development of

"4. More standardization. “artificial" memories are designed to replicate, so

“5. Extended use of integrated or hybrid circuits. far as possible, known neurophysiological phe- “6. Improved methods of packaging for stack and nomena. For example, Borsellino and his colleagues

stack interface circuits to reduce packaging at the University of Genoa are studying physical

and assembly costs. chemical simulation, such as collagen “memories”,

7. Reduced physical size.” (Petschauer, 1967, in terms of possible mechanisms of axon action, connectivity of pulses, and currents through membranes. (Stevens, 1968, p. 31).

With respect to current prospects for much larger,

much faster main memories, Rajchman (1965) We may thus conclude with Licklider that “insofar as memory media are concerned, current

reviews possibilities for integrated construction research and development present many possibil

methods using ferrite aperture plates, thin films, ities. The most immediate prospects advanced for

laminate-diode combinations, field-effect transistors,

and superconductive thin film cryotrons.6.102 It primary memories are thin magnetic films, coated wires, and cryogenic films. For the next echelons,

is noted further that “planar magnetic film memories there are magnetic disks and photographic films and

offer many advantages for applications as main plates. Farther distant are thermoplastics and

computer storage units in the capacity range of

200K to 5M bits." (Simkins, 1967, p. 593), and that photosensitive crystals. Still farther away - almost wholly speculative - are protein molecules and

“perhaps the most significant system advantage other quasi-living structures.” (Licklider, 1965,

available to users of plated magnetic cylindrical

thin film memory elements is a nondestructive pp. 63–64).

readout capability. For main memory use, NDRO 6.3.1. Main Memories

with equal Read-Write drive currents is most ad.

vantageous. It allows the greatest possible flexibility Questions of advanced tehcnological develop- of organization and operation. For maximum econments related to data and program information omy, many memory words (or bytes) may be ac

p. 599).

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