The holography is part of diffraction optics, studying not only the beam, but also wave
aspects of the light. This is a long theoretical tradition in optics, having been established since
the 19 century with the works of Abbe, Lipmann, Breg, Wolfke, and Zehrnike. The father of
holography Denis Gabor (1947) was the first who theoretically proved the possibility of
recording not only the intensity of light - what our eyes, photography, cinema and TV are
doing, but also the phase or period of light. Holography achieves this by registering the spot
of interference between the two light beams - first coming from the object (called "objective"
and hence possessing the information about it) and the second one called "basic” or
"supporting", and which interfere with the objective one.
Insert Image 1 about here (Principle scheme of holographic recording)
The holography appeared as a result of high-tech development in physics after the WW II.
Gabor made his discovery when trying to increase the sensitivity of the first electron
microscopes. In 1955 Emmett Leith and Juris Upatnieks in US reinvented the principle of
holography working on improving the sensitivity of radars. Later their method became the
basic method in holographic research. Only the author of the third type of holography – Yuri
Denisyuk (1961), developed his method in former USSR working on a theoretical problem,
namely the development of the old Lipmann's method of recording and reproducing colour
images. These discoveries enlarged the scope of holographic methods and its possibilities.
However, they remained almost unnoticed and out of the main stream of physics until the
early 1960s.
There are two basic problems the holography has been confronted with since Gabor’s
discovery:
- The producing of coherent, i.e. with fixed length, light beams;
- The design of recording materials with very high discriminative characteristics in
order to register the interference strips.
The first was solved in 1963 was with the discovery of laser, which provided light with
specific qualities (constant longitude and phase) necessary to record a good picture of
interference between the beams. The second problem (if for irreversible, ‘write-once-only’
materials) was solved about the same period of time with the development of
photolithographic technology in electronic industry, using high-resolution materials. Their
properties were similar to those needed for holography. Soon after that the first good quality
3
holograms appeared, followed by various projects for holographic cinema, holographic TV
and video, holographic interferometers, holographic coding and security systems, etc. Not
surprisingly Denis Gabor received the Nobel Prize in 1971 - 24 years after he made his
discovery!
2. Holography and computer technology in the West in 1960s and early 1970s
This section summarised the main research efforts in developed Western countries, based on
our research in the literature and personal interviews with some of the leading scientists at the
time. It pays special attention to the commercial research done by major European companies
in the field. The next section will outline the research on holographic computer memory in
the former Soviet bloc.
The boost of holographic research in mid 1960s coincided with the period of relative
stagnation in computer technology. There were fears that the existing semiconductors and
magnetic recording devices (magnetic tapes and disks) would be unable to meet the growing
demands for faster computers with larger memory. So the superpowers and the major
multinational corporations have been investing heavily in research on alternative models of
computers and memory devices. It was in this field where the most attractive opportunities
for holography had emerged. The theoretical predictions showed that in some cases a
computer memory with the volume of about 10.12 Bytes (1 Gigabyte) might be designed by
using micro-holography and special recording devices, which was far above the possibilities
of magnetic types and disks, known at that time. The holographic storage possessed also
another crucial advantages – unlike classical von Neumann serial (byte by byte) processing of
information, it was based on the principles of the mass parallel input and output, which
promised much higher speed of processing data.
We will briefly outline the major alternative models, which participated in the "battle" for a
new, high volume computer memory:
1. The traditional magnetic memory (magnetic tapes and disks);
2. The memory of the semiconductors (so-called RAM and ROM memories);
3. The optical memory, with two sub-models:
- The holographic memory (HM), able to record not only digital information, but also
to assure massive (parallel) access to the stored data;
- The compact disk (CD), using the same technical principles as magnetic memory
(i.e. "bit by bit" technology, but information was stored at an optical media).
4
4. Magnetic memory using specific phenomena in semiconductors, called "bubble memory".
5. The model of Stan Ovshinsky, an US scientist, using the so-called "amorphous glasses";
6. The "magnetic domains memory", using newly discovered phenomena in semiconductors;
7. The "Josephson effect" (or Josephson junction) memory, using "tunnelling of the
electronic beams in very low temperature".2
Now, with the exception of CD-ROM, most of these alternative models have marginal
existence in the field of solid-state physics. However, they all bloomed in a period of about
ten years between the late 60-s and mid 70-s. Some of them had been developed to the
prototype-level, or even found limited application.
By 1975 in the specialized literature there appeared number of publications, presenting the
results of decade-long research on the holographic computer memory. (See in Appendix 1 the
scientometric analysis of publications in the field). The scope of research that had been
presented comprised predominantly theoretical analysis about feasibility of the holographic
memory, as well as the explorative experimental data about the information capabilities of
this new type of memory.
Insert Image 2 about here (Titles of research papers on holographic storage in late
1960s - early 1970s)
The leading French researcher in the field J.P. Huignard (principle researchers at the
Thomson CSF holographic memory team) adequately summarizes events from the
culmination period of early 1970s. According to him after almost ten years intensive work,
the laboratories have completed one main stage of research and needed a kind of mapping of
what have been done world wide, in order to evaluate their achievements. In the Western
world the final line of the balance sheet was drown at 1974 conference in US:
2 The last two models also seemed promising during a certain period of time. The domain memory was
experimentally used in satellites, being very stable in the environment with high radiation. As far as Josephson
memory is concerned, this is maybe one of the most secret projects, with lot of rumors around it. One of the
scientists I interviewed remembers: "When I visited IBM I was told that if this model proved successful, the
entire knowledge of humanity might be collected in a volume of a glass of water." According to the another
scientist "... In fact the project was completed at prototype level, but its capacity was so high, that it was
estimated that it would hardly be one or two user of this technology. So IBM made everything to stop and to
keep secret this technology. One of the authors of the project told me about that, when I met him in 1985 at a
conference in Novosibirsk, former Soviet Union." I have conducted an explorative scientometric search on these
models and found them very well represented in Science Citation Index. In the data base INSPEC (physics) one
can find the headings 'magnetic bubble devices', 'domain storage', 'Josephson effect' and 'junction devices' as a
part of more general heading of 'superconductivity tunneling'; 'amorphous magnetic materials' and 'amorphous
glasses.
5
“… Ah this meeting only the Japanese had presented a completed prototype – a kind of box
where the main components of holographic memory have been assembled. All the others
reported experimental setups or laboratory models only. It became clear that in spite of the
achievements made we all are still far away from the industrial production.” (From the
interview with the author, 1995)
A good illustration of what was going on in (Western) Europe during this period provides the
letter I got in 1994 from Dr. S. Stork, then deputy director on research at Siemens research lab
in Munich, Germany. It was this lab where in 1970s one of the intensive HM research in
Europe have been carried out. In response to my inquiry for establishing contacts with
researchers working on Siemens’ HM project, he wrote:
“…The scientists, which have been working at SIEMENS on holographic memory, have been
dispersed in many different directions: Dr. Horst Kiemle and Dr. Peter Graff, heads of the
research group at that time, have been retired... Prof. Dr. Manfred Lang, another head, has
gotten a professorial chair on “Human-Machine Communication” at Technical University in
Munich. Dr. Hartwig Rüll, who also worked on holographic storage in time-dependent signal,
is engaged with Business Planning department at Siemens’ headquarter in Munich.” (From
the letter to the author, 1994)
When it became clear that commercial applications of holographic memory would not come
soon, that they will require new investments and new years of research, Siemens simply
closed down its team. Phillips, Thomson CSF and other big European computer companies
soon followed it. After the 1974 conference in US most of these companies gradually
withdraw from HM research, at best redirecting their teams to the neighbour areas with better
chances for commercial success, for example in the field of pattern recognition. However,
military oriented research has continued all over the Could War, although a few of them went
public. Only after 1990 there appeared publications about holographic archive with high-
resolution geographical maps, which have been in operation for many years at US strategic
aviation commandment; about holographic memory devices working on satellites; about
Optical Holographic Missile Seeker at the guiding head of US missile MICON, etc. The
firms’ research on commercial holographic memory, however, had practically stopped.
3. Holographic storage in the Soviet Bloc. The Bulgarian ‘connection’
This section traces briefly the main research centres on holographic computer memory in
former COMECON to focus on the case of Bulgaria as one of the latecomers in the field. It
analyses the particular political and economic circumstances that allowed the investments in
this type of research and the crucial role of few holographic memory enthusiasts in the
community of Bulgarian physicists.
6
Like in the Western countries, since mid 1960s on the other side of Iron Curtain there were
also intensive researches in holographic computer memory going on. In the former USSR
several research groups existed, each working on its own version of memory devices. There
were two groups in the region of Moscow, one in Kiev, one in Novosibirsk, and one in
Leningrad (now Saint Petersburg). Researches on holographic memory have been carried out
also in Poland, former GDR, Czechoslovakia, and Bulgaria.
During this period the Soviet holographic research community was engaged in heated
discussions, the main forum being the All-Soviet (Summer) School on Holography. Initially it
was closed for the foreigners, but since early 1970s some researchers from the other socialist
countries, including Bulgaria, have been admitted. Unlike the situation in the West, where in
the second half of 1970s a sharp decline of holographic memory research could be found, in
the former socialist countries the mass research efforts have continued till the beginning of
1980s, while in some laboratories they continued till the early 1990s! Once recognized as
strategic field of research, administrative system was able to provide long-term investments,
independently of the prospects of their return. In this respect the Bulgarian case was
especially revealing.
The meeting at Communist Party Central Committee
In a late autumn morning of 1974, a group of people, bewildered, was waiting in front of the
office of Todor Zhivkov - First Secretary of the Bulgarian Communist Party and President of
the country. Among them were highly ranked functionaries, ministers, and professors from
the Bulgarian Academy of Sciences. Including a 33 years old physicist, who had just
surrendered at the entrance checkpoint a briefcase with research equipment and files with
drawings and formulae. Methodius, the physicist, remembered:
"When we came in and those present were introduced, I realized that everything had been
prepared in advance. Zhivkov explained the object of the meeting and gave me the floor. I
reported our findings and their possible applications. I took out a small helium-neon laser and
plate patterns from the briefcase, and reproduced the holograms on the spot. Out of each of
them, with an area of less than one square millimetre, an entire page of text appeared on the
screen. Then, out of the other plate I showed them the red-and-black three-dimensional image
of Bulgarian national hero… It was 1974 - most of those present saw a laser in action for the
first time! When the demonstrations were over, Zhivkov said: "That was it. Now, what are we
going to do?" No one wanted to say what was to be done. Zhivkov even got a little angry,
pounded on the table and exclaimed: "This man, these people must be given an opportunity to
work!” and he started dictating: the Council of Ministers was to issue a directive for the
establishment of a laboratory... Then a few found the courage to object that it was premature.
Rather harshly, the First Secretary replied that they were short-sighted and could not see the
strategic importance of this area of research." (From the interview with the author, 1994)
7
Thus, six months later, in the spring of 1975 the Central Laboratory for Optical Storage and
Processing of Information (CLOSPI) was established with the official aim of “conducting
fundamental and applied research in the area”. It was clear to everyone, however, that the
strategic task was the holographic storage that was to make a real revolution in computer
industry. More than $1 million were allocated, the Council of Ministers met and issued
ordinances, laboratories and personnel were moved, overseas representative offices made the
utmost efforts to break through the Western embargo and to equip the laboratory. Specialized
construction work had begun on a new vibration-insulated building for the laboratory.
What made the meeting at Zhivkov’s office possible?
Bulgaria has joined the race in building commercial holographic computer memory with
some 7-8 years delay. The establishment of CLOSPI was not just voluntary act of Communist
party leader, but it marked a specific stage in development of country’s electronic industry.
In the early 1960s, faced with the development in USA and other Western countries,
COMECOM prepared a plan for development of electronic industry. And there appeared a
man in the highest level of Bulgarian hierarchy – Prof. Ivan Popov, who voiced his
conclusion that this new industry gives real chance the country to take more advantageous
position in COMECOM.3 For it was for the first time after WW II when Bulgarian industry
was in an equal ground with its partners - none of socialist countries them possessed enough
experience in commercial computer technology.
How was the Popov’s plan carried out? - First he went to Japan and initiated negotiations
with Japanese firm Fujitsu Co. to buy a license for their FACOM magnetic tape memory
device. At the same time he organized several research and engineering teams at home, which
begin intensive reverse engineering of FACOM device. After careful planning in 1968 he
initiated simultaneous the construction of seven plants, which created the skeleton of the
electronic industry in the country. These activities were in the eve of the eager competition in
3 One of his collaborators remember: "... Ivan Popov was an engineer with very high qualification and knew
perfectly several languages. He was capable to work 16 hours per day, and he does not hesitated to take risks.
He originated from relatively wealthy family, but already in high school he joined communist movements. In
1930s he graduated engineering in France, then he worked few years for AEG in Germany, and later in GANZ
Electrical Works. After WW II he came back in Bulgaria at first as director of the Sofia electro-technical plant,
to became later president of the new ELPROM State Combine, comprising all electro-technical works in the
country. In 1960s Popov was appointed the head of the Bulgarian ministry of research (the so-called State
Committee for Science and Technical Progress - SCSTP), then he became minister of machine-building
industry, and later member of Communist Party Politburo. In political gambits at the top of communist
hierarchy his political career halted suddenly in mid 1970s, when he was blamed for authoritarian (!) approach,
lack of discipline, managerial failures, etc., and dismissed.
8
Soviet bloc about who will be the first to start the production of magnetic memory devices.
Poland, Hungary, Czechoslovakia and USSR had already developed their prototypes, while
Bulgaria was still at the beginning. In the fall of 1968 the COMECOM commission on new
technologies had planed a workshop, where a decision was to be taken who will be principal
producer of these devices. The unbreakable condition was more than 95% of the components
in-build in these devices to be produced inside the COMECOM.
Once the reverse engineering work was completed, Ivan Popov invited the president of
Fujitsu Co. in one of the newly built plants to see the assembly line with first five Bulgarian
clones of FACOM device, and he proposed instead of buying a license to sign a long-term
contract for purchase of determinate number of electronic components in exchange of the
right to produce and sell the copied devices in COMECOM. After long and difficult
negotiations Fujitsu Co. accepted collaboration, and even proposed to train Bulgarian
engineers in debugging. When few months later the workshop of COMECOM committee
was held and each socialist country presented its prototype, the Bulgarian (Fujitsu) machine
demonstrated the best parameters and the country gained the specialization. After this
success, Ivan Popov applied the same strategy in developing disk memory devices, this time
copying the relevant IBM technology. The country soon became the main producer of tape
and disk memory devices for mainframe computers in the former socialist bloc, and took part
in the production of the COMECOM replica of IBM mainframe computers and DEC
minicomputers.4
It was clear enough for Ivan Popov and some of his collaborators, that this imitative strategy
will not be successful in long term if not assisted by in-house fundamental and applied
research, helping the industry to develop original products. With growing income from the
export, the electronic industry begun to provide significant part of the budget of relevant
institutes at the Academy of Sciences and started developing its own R&D facilities. Prof. M.
Borisov, the head of Sofia Institute of Solid State Physics in early 1970s remembered:
"The strategy of Ivan Popov was to integrate the research work in the Physical institute, and
the work of Bulgarian physicists as whole, with the development of electronics. In 1970 the
new R&D Institute of semiconductors proposed to my Institute to prepare an analysis of the
latest achievements in field, which bear on the further development of electronics. So we
4 Since the early 1970s the electronic industry provided about 28% of Bulgarian industrial output and 40% of
the output of electronics in the former COMECOM. The main part came from eight large vertically integrated
production organizations, served by five big R&D institutes and an interdisciplinary coordinating center in the
Bulgarian Academy of Sciences (BAS). A total of 130 000 people had been working in the sector, 8 000 of
whom were highly qualified engineers. (See Run and Utt 1990, pp.22-1).
9
signed a contract and in a year time we prepared the report. They paid good money for this
overview, because they had no enough qualified personnel." (From the interview with the
author, 1993)
The report analyzed the latest discoveries in physics - new materials, semiconductors, lasers,
optical fibres, coherent optics, etc., and their possible technological applications. There was a
special chapter on "optical memory devices", where on could read that "...the development of
laser, the advances in guidance of light beams, and the development of holography opened
possibility for the development of optical computers with higher speed of processing and
enormous density of recording of information, which can not be achieved with the existing
magnetic electronic technology." In the paragraph on “holographic memory devices” some
additional advantages were pointed out - "new associative type of memory", "parallel
computing", increased stability and low signal-to-noise ratio, etc. This report has never been
published officially, but it was largely distributed among the managers of electronic industry
and the high level Communist Party and state officials.
In another evidence comes from the interview with one of leading engineers of the first
magnetic tape memory device. He remembered about a conference on the perspectives
electronic industry, organized by Bulgarian Ministry of electronics in 1972:
"... In my report I stressed the fact that during the last few years publications on optical
memories practically disappeared. I said this is a sign of transition from fundamental to
applied research and semi-industrial prototypes. Now the firms are protecting their results and
are preparing for large-scale production. If we want to be close after the leaders, we were to
develop research potential in this area, too." (From the interview with the author, 1994)
This report also raised significant interest and later was published in a booklet. Hence in early
1970s the ideas of holographic storage (and optoelectronics in general) as near future of
contemporary electronics was spread enough in high level of Bulgarian political and
industrial decision-making. The National Program for development in the field of laser
technology was established aiming at production of various types of lasers together with their
technological applications. It was structured on the simple typology: 1) collecting of
information, i.e. laser-location, laser sensors, etc.; 2) communication via laser beam in free
space and/or optical fibres; 3) information processing and storage. The main task in the later
was holographic computer memory. Typically for the style of management at that period, the
creation of a large Institute of laser technology was planned, which was supposed to unite the
efforts of several different research groups working in the field. One of the authors of the
Program stated in the interview:
"...We have almost completed the Programme and it was discussed with the Ruling Board of
the Academy of sciences. Academician Djakov, one of the highly estimated Bulgarian
10
physicists, gave its approval. Almost everything necessary was done. Then suddenly came the
Government’s decision for establishing CLOSPI. That is how Methodius destroyed our
Program. He came with some direct channels to the Central Committee." (From the interview
with the author, 1995)
The failures and successes of holographic memory research in the East
When CLOSPI was founded, its staff began researching in several inter-related directions
following the theoretical scheme of holographic storage - photosensitive materials, special
micro-optical elements, systems for in-put and out-put of information, etc. After several years
of work it became evident that the initially formulated objective would hardly be obtained:
despite the efforts the characteristics of the reversible storage media (photo-refractive
crystals) improved very slowly; the designed electromechanical deflection device guiding the
laser beams also proved unreliable; there were problems with the input and output systems,
etc. When in 1978 Methodius as director of the lab was summoned to report the progress of
holographic memory research to the Ministry of Industry, he showed the plates for art
holograms, diffraction gratings, some micro-lenses for the yet not ready input device, etc.
The head of the Ministry Ognian Doinov told him: “Fine, but it is far more important to have
this memory!”
Next year the laboratory was again visited by high-ranking state and Communist Party
officials, as well as by a delegation of the Soviet Academy of Sciences headed by
academician Alexander Prohorov (1971 Nobel Prize winner). After these visits a special
meeting was held where a general analysis of the execution of the project was made. The
assessment was generally positive, but the conclusion said that the desired optical memory
couldn’t be created in a short period of time. Soon after that the cheer funding vanished. The
dream of holographic storage, the "great computer memory" to make a real revolution in
computer industry, had slowly faded away…
The holographic “island of haven” in the East
The destiny of Bulgarian lab was typical for the similar labs in other East-European countries
and former Soviet Union. Facing the need of continuous investment without certainty for near
commercial success, the communist leader – much like the presidents of Western
corporations, cut the funding.5 Yet like in the West, there were exceptions – these are most of
laboratories, whose researches were closely related with military or similar type of priorities.
5 It can’t be said, however, that communist leaders steering electronic industry had the same economic motives
like managers of Western corporations. As Janos Kornai has pointed out, in the socialist administrative economy
11
One such unit was the Institute of Automation and Electrometry (IAE) at the Siberian Branch
of Russian Academy of Sciences (RAS) in Novosibirsk, established in early 1970s. The IAE
managed to design a working memory device for write only (archive) storage. This
remarkable achievement was the result of more than twenty years continuous research, due to
the efforts of IAE director Prof. Petr Tverdokhleb and his colleagues. The team worked in
close collaboration with the research labs and engineering design bureaus at military-
industrial complex in Novosibirsk region. The history of this lab merit separate book. What
backed their efforts was the task to provide reliable computer archive for the Soviet space
program, which had accumulated a bulk of telemetric and other data. Being stored in
magnetic tapes and disks, it needed renovating every 10 to 15 years due to the degradation of
the magnetic media. Holographic memory proved to be one of the best solutions, because of
its high reliability and the long life of the recording media (50 and more years). It was found
also, that due to the specific properties of this media (dichromated gelatine plates), the quality
of holographic recording even improves over the time of storage.
The Novosibirsk team had successfully passed through the number of technological
bottlenecks, and had gained unique research and engineering experience, which made them
one of the tope experts in the field. It is not at random that in the 1995 volume on holographic
memory research worldwide, published in 1995 in US (Sincerbox 1995), this team was
among the few groups represented with several publications (the other were Huignard from
Thomson CSF lab and Hesselink from US). When we visited IAE in 1995, we have found a
completely developed technology for write-only holographic computer memory. During the
twenty years of research the team had solved number of extremely difficult problems of the
input of computer information and its formatting into binary coded ‘pages’, their precise
recording at microscopic areas on the holographic plate, its subsequent addressing, reading,
and transferring again into electronic output, etc. They have designed also coding and error
correction algorithms, specific for the holographic recording system. But maybe their most
important achievement was the miniaturization of the device, so that they were able to show
us a working 1.2 Gigabyte holographic memory plate designed already in late 1980s, with the
size of standard 1.44 MB floppy diskette. I was pleased to learn that first successful
the industrial success possessed not only commercial value in narrow sense, but also equally important
ideological value – as yet another prove about the supremacy of the socialist economic system. (See Kornai
1992, chapter 9- “Investments and Growth”). That is why in the political games inside the communist
nomenclature, the long-term investments in new technologies having uncertain success have often been avoided.
(See Tchalakov 2004)
12
prototypes have worked with high-resolution holographic plates created by their Bulgarian
colleagues in CLOSPI.
Insert Image 3 about here (Holographic archive memory device designed at IAE,
Novosibirsk in late 1980s)
Insert Image 4 about here (Holographic cassette containing 1.2 Gigabytes of data)
My visit in the Novosibirsk, however, coincided with period when the lab gradually
recovered after the shocks it had experienced few years earlier. The replacement of the IAE
director, together with the severe financial and economic crisis in Russia in the beginning of
1990s had halted the research for several years.Most of the members of the team had been
dispersed, and part of the hardware was destroyed. The unique technological skills and know-
how were on the eve of dissipation. Prof. Tverdokhleb barely survived it – he got a heart
attack and it took him several years until he returned to work. At the time of our visit in 1995
the hope was in the revival of the interest on holographic memory in mid 1990s, and the
readiness of Western and Chinese colleagues to collaborate with the team. The years that
followed conferment the hopes were not groundless.
4. The difficulties that prevented holographic computer memory revolution
from 1970s to happen
The holographic archive designed at Novosibirsk was completed in the late 1980s. In the mid
1970s, however, most of their achievements were yet to come. This section summarises the
main problems holographic computer memory research had faced in 1970s, which prevented
its commercial realisation. Using the language of the holographic scientists themselves, it
defines these problems in two groups, which could be roughly named ‘technical’ and ‘social’,
although the analysis of Bulgarian case above clearly demonstrated that this distinction
cannot endure a closer look of what was going on in the laboratories and their environments.
The ‘technical’ problems of holographic storage
Let us consider the principle model of holographic optical memory, as it gradually emerged
in the course of earlier research both at the East and West. Our point of departure is the
model, describe in 1977 by the leading Soviet researchers Akaev and Majorov, and which
summarized the world achievements at the time. (See Akaev and Majorov 1977). According
to this model the holographic memory device included the following main elements: laser,
spatial modulator, deflector, recording media, photo-detectors, and optical elements.
13
Insert Image 5 about here (Holographic Storage System).
As seen from the account of Dr. Huignard we cited in the second section, the key unsolved
technical problems of holographic storage were defined in early 1970. Most of them are
related with the level of miniaturization. This issue did not seem so important at the
beginning, but it had gradually come to the fore with the course of research. The essence of
this problem is adequately given in a piece from my 1994 interview with Prof. Juergen Jahns,
a leading German optical scientists, who had been working for many years in ATT Bell Labs
in New Jersey:
" The conventional three space optical systems... It is a totally different world of what the
electronic industry is used to! In the electronic industry they are using two-dimensional chips;
they use computer-aided design... This is a miniaturized world, while if you look at the
conventional opto-mechanics - you have a big optical table, you have a very specialized
knowledge that is necessary to build such a system. When people were talking about optical
computer until recently they basically were talking about using a 19-century technology for
building the computer of 21 century!" (From the interview with the author, 1994)
In spite of the technological development the 1970s’, the lasers - as one of the main
components of the designed holographic memory – remained big enough and not easily built
into a compact and reliable device. They consumed also lot of energy and dissipated heat,
which added cooling problems to the design. The breakthrough happened only in the second
part of 1980s, after many years of intensive research that had led to some key discoveries,
such as the mid-1980s discovery of David Miller and his colleagues at ATT Bell Labs about
the vertical cavity surface emitting laser (VCSEL) based on self-electro-optic effect (SEED).
This discovery made possible the design of chips with thousands of micro-lasers in a surface
of squired centimetre.
Working with single lasers, the holographic storage designed in 1960s and 1970s required the
deflection of the beam. The existing electro-mechanical, acousto-optic and magneto-optic
deflectors were far away from the needed accuracy and speed. All scientists and engineers I
had interviewed univocally claimed that in 1970s the lack of appropriate deflectors was one
of the major obstacles in the development of the new technology. No one succeeded to design
a device that was compact, fast, reliable and economic enough, and which was able to address
the laser beam simultaneously at x and y coordinates of the plane (not to think about x, y and
z space). In fact the problem have been solved decades later using VCSEL technology – the
so-called smart pixel arrays integrating thousands, now even millions individually guided
microscopic lasers, working at speed of nanoseconds.
14
On the material side the lack of reversible recording media, compatible with magnetic
materials used by conventional electronics, was considered as another major obstacle.
Practically all publications from that period discussed the problem of the lack of reversible
recording media. The best recording materials – silver-halide plates, were very robust and
lasted for many decades permitting practically unlimited reading of the stored data. However,
they had the major disadvantage of being write-once materials, i.e. their properties changes
irreversibly after the initial recording. They were excellent for data archives, which saved the
research program of Novosibirsk laboratory, but the mass introduction of holographic storage
in computer industry required reversible media. During the 1970s the most promising
candidates for such reversible media were photorefractive crystals (like Bi12SiO20), which
were very expensive and difficult to master, while the ‘life’ of the stored data remained
relatively short – weeks, rarely months. It was at that period when the work on organic
reversible media had begin, the so-called photo-polymers. Eventually such materials did
appeared at the end of 1980s, when Dupont in USA patented the first photo-polymer
permitting reversible high-quality recording of holograms and which ‘remembered’ the data
for many months and even years. In addition, the new materials were much cheaper than
photorefractive crystals.
The next important problem the 1960s and 1970s research had to deal with was the low
capacity of the existing electronic input and output devices. The difficulties stemmed from
the fact that holographic storage is inherently parallel, i.e. it store simultaneously (in single
‘flash’) massive data of thousand and tens of thousands bites, while computers are working
up until recently in serial way – by steps of limited number of bits. Hence the needs of
temporary ‘storage rooms’ in order to accumulate the serial information coming from the
computers and to transform it into parallel one. This incompatibility of underlying principles
of data processing in holographic devices and (then) electronic computers had greatly
reduced the theoretically proven higher speed of holographic storage.
The ‘social’ difficulties holographic storage had faced with: human resources and
investment problems.
While holographic memory research were dealing with these ‘technical’ problems, already in
mid 1970s it gradually became evident that traditional magnetic memory technologies were
again gaining momentum and threatened to erode the (theoretically predicted) advantages of
holographic storage. Due to the enormous investments, the technical parameters of the
existing magnetic memory devices had been gradually improved. Below we provide a
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comparison of the development of magnetic disk memory technology in the world-leading
producer IBM and the leading producer of magnetic memory in former COMECOM, the
Bulgarian state combine IZOT:
Chart 1 Relative development delay of magnetic disk technology in Bulgaria
0
50
100
150
200
250
1955 1960 1965 1970 1975 1980 1985year of production
Disk volume
in MBIBM
IZOT
The table show that the time lag between the products of the two companies remained
practically the same, i.e. the IZOT’s strategy in copying the latest IBM devices did not
allowed an originally technology to emerge. But it also clearly demonstrates the speed of
development of the magnetic disk technology, which in less than 10 years improved almost
30 times - from the first 7 megabytes disk IBM released in 1964 to its 200 MB disk produced
in 1973! Not to mention the fact that the latest disks were much smaller and reliable than the
first models. This process continues till the present days, but already in mid-1970s it softened
the previous urgent necessity of new computer memory technology, which in turn diminished
the generous investments in alternative researches like holographic memory.
There was, however, another barrier to the introduction of holographic memory, which
remained almost unnoticed for quite along time. Prof. Kraftzig from the Osnabruek
University in Germany, who had been working in the Phillips optical laboratories during the
1970-s, said in the interview:
“…The compact disks, the videodisks were completely ready in the research laboratories at
the end of 1960-s. But it took 10 to 15 years until these very simple systems came on the
market! Because it was discovered that optics is not so simple to handle and all engineers they
are used to work with electronic systems, but not with optical systems. Well, and this is not
the real coherent light. If you want to build the system with coherent light [like holographic
memories – I.Tch.] the difficulties will be much larger.” (From the interview with the author,
1994)
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What doest it means that “optics is not so simple to handle and all engineers they are used to
work with electronic systems”? - Prof. Adolph Lohmann, one of the founding fathers of
modern holography6, provided the clue to understand this problem:
"…The optical computer did not succeed until now not only because of the lack of
sufficiently enough investments, but also due to the fact that the number of the electronic
engineers is perhaps hundred times higher than that of optics engineers and scientists working
in the field of optics. So you cannot say: "By next year I want some 10 000 optics people
trained". No one is able to accomplish something provided there is no manpower.
- Why is it so difficult for scientists and engineers educated in electronics to switch to optics?
- For one thing, the electronic engineers usually deal with temporal signals, which are one-
dimensional. While the optics engineers deal with two coordinates, sometimes even with
three coordinates. And this is not so easy to change... Electronics people usually say: "Every
electron is completely supervised!” - just like every person in a dictatorship is. Whereas with
the photons moving in free space there are some steps where no one can supervise them,
where they are left free. The photons are much more "democratic" than the electrons. That is
why electronics people are afraid: If you let photons go out will you be able to catch them
again? - They want to have the photons controlled, to keep the central power in their hands.
So whenever optics and electronics people work together, the electronics people usually say:
"Let's take central control!" while the optical men always object saying: "No, let's take self-
rooting!” The optic people prefer very loose government whereas electronics people have
very strong government. Electrons are not as free as photons..." (From the interview with the
author, 1995)
Prof. Lohmann thought it needed generational change in order such a radical shift in
production technologies to take place. Comparing with electronics, the optics was a rather
different culture, different ‘form of life’, and he did not considered this simply as
‘knowledge’ processes: in 1960s and 1970s, he said, the electronic people have been on
power; they had the command positions in the industry. So when they had to decide on
investments and when technological choices had to be maid, they followed their own way,
the way they knew the best. And to this added the miniaturization, which had already became
essential part of the culture of electronics and to which optics people had long way to go.7
Conclusion
Our analysis of the development of holographic memory research demonstrated that although
in different institutional, economic and political setting, the holographic memory research at
the both side of the Iron Curtain followed the fairly similar patterns.
6 Prof. Adolph Lohmann was the man who invented the computer-generated holograms and who after working
for many years in IBM labs in California, had returned in 1967s in Germany to establish the Applied Optics
Department in University Erlangen-Nürnberg, today one of the center of optoelectronic research in this country. 7 Another evidence in this direction from the interview with A. Lohmann: “ In the beginning the optical
laboratories were large. Electronic engineers when visited us they said: "This large system can work with 10 bits
per second? We do 10 bit per second in our micro..." So if one wants the marriage between two technologies,
then there the size should be somewhat compatible. Hence the optics people have to learn to do things smaller.”
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Firsts, there were equally heavy investments in research with government funding playing an
important role at the initial stage. The prospects for possible military application of the new
technology had been important incentive both at the East and the West. At first glance the
Western companies seemed to be much more flexible than their Eastern counterparts. They
switched to another options or simply cut off the funding when it became clear that results
would come longer than expected. In the Eastern block the rigidity of administrative system
and (declared) strategic importance of the field helped some research teams to continue their
work long enough. Yet this claim is uncertain, because many holographic memory teams in
Eastern Europe did closed their work (as was the case in Bulgaria), while rumours says,
although we did not managed to check it in place, that some US and Japanese companies like
Matsushita had continued their research long after the decisive conference in USA in 1974.
Second, we have clearly identified the ‘reverse salient’ phenomenon discovered by Tomas
Hughes, where the clearly defined and widely recognized technical difficulties have focused
the efforts of many research groups. However, the story of the first wave of holographic
memory research has demonstrated that often the long searched solution came from
seemingly occasional breakthroughs in relatively independent areas, which opened new
research possibilities and modified the previous design schemes. This was clearly the case
with Miller’s VCSEL devices or Dupont’s photopolymers.
Third, behind the technical difficulties, investment problems, etc., the new optic technology
in computing was calling for a radical technological shift and inspired a new way of
designing the computing systems. The direct clash between the two storage technologies
(magnetic and optic) that took place in 1970s was to be resolved not in direct assault, but by
mutual tuning in of the two ‘people’ and by slow incremental steps. A few suspected the gap
between ‘electronics’ and ‘optics’ people was so big.
However, there were two important differences between holographic computer memory
researches at the two sides of Iron Curtain. One was the level of secrecy – holographic
research in the Soviet bloc had been carried out in much greater secrecy and an evidence for
that is the time lag in scientific publications, which followed those in the West journals with
few years delay. The Soviet holographic community was initially closed even for the
researchers from former socialist countries! The second difference concerns the location of
major R&D efforts – in the former Soviet bloc the researches were carried out mostly in the
Academies of Sciences’ institutes, while in the Western countries (at least in Europe) they
were company-based - Siemens, Phillips, Thomson-CSF, Matsushita, etc.
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Finally, our study confirmed the well know fact in the history of technology about the
importance of keeping research teams long enough working on specific problems. This made
possible the accumulation of unique experience to handle specific type of non-human entities
and made these teams prepared to catch the ‘occasionally’ emerged possibilities in other
fields of research. Also, the cross-fertilisation between electronic and optic technology
community seemed very important for the eventual success of the later – the IAE holographic
archive in Novosibirsk clearly demonstrate this. The much stronger evidence in this direction
is the work of Prof. Juergen Jahns. After his graduation in Erlangen as Prof. Lohmann PhD
student, he spend eight years at ATT Bell Labs in New Jersey to became together with Alan
Huang one of the inventors of planar optics - one of the most promising avenue for
integration of optics into computer systems (see Jahns and Huang 1989). But this is an event
from the ongoing ‘second wave’ of optical research in computers, which merit another
discussion.
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List of images
Image 1 Principle scheme of holographic recording
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Image 2 Some titles from the research papers on holographic storage from late 1960s
and early 1970s
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Image 3 Holographic archive memory device designed at IAE, Novosibirsk in late
1980s. (Pictures courtesy P. Tverdokhleb and E. Pen, IAE – RAS, Novosibirsk)
The round containers on the top hold the 1.2 GB holographic cassettes, which a small robot
in the centre put in and out of the reading set-up. At the bottom of the image one sees two
working place with computer terminals.
Image 4 Holographic cassette containing 1.2 Gigabytes of data. (See the one-cent coin
sized at the bottom right)
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Image 5 Holographic Storage System (principle scheme)
The elements of holographic memory: 1) Laser, 2) Spatial modulator, 3) Deflector,
