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European Science Foundation publishes four year plan

The European Science Foundation is an association of 62 major national funding agencies devoted to scientific research in 21 countries. The ESF assists its member organizations in two main ways: by bringing scientists together in its scientific programmes; and through the joint study of issues of strategic importance in European science policy.

The plan splits the foundation’s activities into eight separate themes: the solid Earth; environmental processes; resources and sustainability; atoms, molecules and complex physical systems; the brain and cognitive sciences; genomes and genome products; health issues; culture and the European identity.

Physics research will be covered by the theme on atoms, molecules and complex physical systems. This will include research into: matter at extreme scales and conditions; the study and creation of novel materials and molecules; nonlinear dynamic systems; and advanced computing methods.

The report also discusses how the foundation could improve its network of workshops, programmes and conferences, and predicts the ESF budget over the next four years. During this time the foundation expects that its budget will only grow by 1 per cent as nearly all of the foundation’s member organizations are under tight financial constraints.

Sir Dai Rees, ESF president, and Peter Fricker, secretary general, said in a joint statement that they hoped that the report will help encourage science within Europe. “The ESF’s ‘science-driven’ actions are complementary to those of other agencies, such as the European Commission, which primarily focus on the benefits to be obtained from science, ” they said. “The ESF has an important role to play in spearheading scientific advances and in providing scientific strengths upon which other agencies’ actions can build.”

Under funding of UK research nears “crisis proportions”

The Implications of the Dearing Report for the Structure and Funding of University Research calls for the government to immediately invest £410 – £430 million in the UK’s research infrastructure, and contains some 37 recommendation and conclusions on the Dearing report.

The committee’s main concern is the effect that the Dearing report will have on UK university research, and the knock-on effect on the future long-term economic growth and quality of life. “Under funding in university research is nearing crisis proportions. In particular, under investment in laboratories and research equipment is undermining researchers’ ability to attract private sector research funding and to conduct research at the cutting edge, ” says Michael Clark, the Chairman of the Committee.

The committee also places some blame on the universities by suggesting that they do not include the true cost of research in their grant applications. It proposes that charities, private companies and public bodies, such as the research councils, should pay for the full indirect costs of research, excluding staff salaries, of all their university funded research. These costs would be based on a sliding scale that depended on the type of research funded.

Like Dearing, the committee also approves of universities conducting frequent reviews of their research activities. However, it disagrees with Dearing’s proposals to direct research funds into a small select group of research-based universities. The committee also claims that such an approach would not resolve the current crisis, nor guarantee the long-term future of UK research.

Astronomers focus on thefuture

The meeting, attended by 200 astronomers, discussed the future of more than 40 facilities and drew up a plan to provide a basis for budget discussions with the ministry for education and research. It strongly supports France’s continued participation in the European Southern Observatory and several other international projects.

However, cuts to the astronomy facilities budget are inevitable as the government directs money away from large facilities and towards shorter-term projects. The 1998 budget for large astronomical facilities will be cut from FFr 730m (about £71m) to FFr 700m. And the research ministry is seeking another FFr 20m in cuts, according to Jean-Pierre Gratin, who is responsible for astronomy at the ministry.

To save money, the research minister, Claude Allègre, last year proposed reducing France’s FFr 130m subscription to the European Southern Observatory (ESO) by FFr 30m. However, after tough discussions, Allègre agreed to a FFr 10m cut.

The astronomers at Arcachon also backed the Institute for Millimetre Radio Astronomy (IRAM) based in Grenoble. The facility is a collaboration between France, Germany and Spain.

Of the space programmes, the next-generation space telescope (a successor to the Hubble telescope that is due for launch in 2007) and Mars Express (a European Space Agency project due for launch in 2003) also won strong support.

Potential losers include the European incoherent scatter radar, a joint project to study the ionosphere that is financed by France and six other countries. The meeting discussed reducing France’s contribution to the facility – which cost FFr 194m to construct – from 23% to 15%.

Another potential loser is the solar telescope THEMIS, currently funded 80% by France and 20% by Italy. Participants praised the project – which cost FFr 87m to build – but recommended asking other European countries to help cover the FFr 6m annual running costs.

France’s many small national telescopes may also lose funding. There are plans to move them under the partial control of their user communities, with the users picking up much of the bill for their maintenance. And the Canada-France-Hawaii 4 m optical telescope in Hawaii looks set to end operation in 2005.

Students face hard choices

The University and College Admissions Service says that applications for undergraduate physics courses have fallen by just 1.2%, compared with a drop of 4.2% in all subjects. It has received 17 377 applications for physics entry later this year, with each student making an average of 5.2 applications.

UK physics students can either do a three-year BSc course or one of the new four-year MPhys degrees. When the MPhys degree was launched, the intention was that most students who wanted to do a PhD would choose to do the four-year course, but it is not clear if this is happening.

John Edgington, a particle physicist from Queen Mary and Westfield College, London, is surveying all of the UK physics departments to find out. He points out that as long as the research councils continue to award PhD studentships to those who have completed three-year courses, “many able students will prefer not to take four years over their undergraduate studies”.

Money is also an important factor. From next autumn, all undergraduate students whose parents earn more than £16 000 will have to pay tuition fees of up to £1000 a year, while grants to pay for living costs will be replaced entirely by loans. This could put potential students off the longer degrees and have a knock-on effect on PhDs.

Peter Main, who runs the MPhys programme at Nottingham University, is well aware of the problem. “What incentive is there for a student in debt to stay on a subsistence income for a three further years doing a PhD, when they could be earning a starting salary of £19-20 000?” he asks.

EU investment falls behind

The report, which analyses data ranging from global trends in R&D expenditure to patterns of research mobility, was published by the European Commission last month. It aims to inform and guide future policy-making.

The EU’s share of global R&D expenditure was 26.9% in 1995, representing a fall of about 1% since 1980. The EU now spends 1.8% of its gross domestic product (GDP) on R&D, a lower proportion than the US (2.2%), the developed Asian economies (2.7%) and countries such as Iceland, Norway and Switzerland (2.1%). But the EU lags furthest behind in the percentage of GDP spent on industrial R&D (1.1%) compared with the US (1.77%) and Japan (1.95%).

The EU does well, however, in the number of scientific papers published and between 1980 and 1995, it overtook the US. However, the average number of citations per paper was lower in the EU (1.05) than in the US (1.4). South-east Asia lags behind with a citation index of 0.84.

The EU has not done so well with patents, although by 1992 the decline of the previous three years had halted. Japan has overtaken the US in the number of patents filed per employee, and has maintained that lead despite a setback in the early 1990s. The EU is strongest in patents related to the aerospace, chemical, pharmaceutical and motor vehicle industries, and weakest in computers, electronics and instruments. The number of patents filed in the latter three areas actually declined between 1993 and 1995.

The increase in the volume of high-tech products in exports indicates the extent to which technological advance has boosted economic growth. The EU’s exports of high-tech products grew rapidly in the 1990s, says the report, although there was wide variation in this growth between member states. Ireland leads the way with 40% of its exports being high-tech; the UK is second with 20%. Despite this growth, however, the EU share of global exports of high-tech products slipped from 28% to 21% between 1990 and 1995. The US share of this market also decreased over the same period, indicating a rise in the strength of Japan and the developed Asian economies. Nonetheless, the US market share remained higher than either the EU or Japan.

The report also documents the growing role of European collaboration. One of the tangible benefits of collaboration is that internationally authored papers are significantly more cited than nationally authored ones. In some countries with a weak science and technology base, having a foreign author doubles the chance of being cited, according to the report.

Europe’s aerospace firms stick to their guns

Officials from all three countries are concerned at the rapid spate of mergers in the US defence and aerospace industry, and hope that a European equivalent can be created to compete against the Americans. Ideally they would like such a European defence giant to be created by this time next year.

The report was issued by members of the Airbus consortium: British Aerospace (UK), Aerospatiale (France), CASA (Spain) and Daimler-Benz Aerospace (Germany). However, the report has ignored the governments’ request to set a timetable for restructuring the industry.

One of the largest stumbling blocks appears to be the state ownership of Aerospatiale. British Aerospace and Daimler-Benz are unenthusiastic about merging with a state-controlled company. They believe that the French government would try to implement French industrial policy through such a merger. The French meanwhile fear that the merger could lead to competitive tendering for the supply of components to the merged company and that this might lead to job losses in French aerospace companies, which are generally less efficient than their German and British counterparts.

Smaller areas such as missiles and electronics companies may merge before any large scale restructuring in the industry.

Response from the various governments to the report have so far been muted. France’s defence minister, Alain Richard, has called for the French company Dassault Aviation and British Aerospace to work more closely on combat aircraft. Dassault Aviation is shortly to merge with Aerospatiale.

George Robinson, UK defence minister, and Margaret Beckett, UK minister for trade and industry, issued a joint statement that welcomed the report, but raised a number of concerns at the pace of change. “The UK government remains convinced that urgent restructuring of Europe’s aerospace industry is essential, ” they said. In Germany, Chancellor Kohl said that he hoped that the report meant there was now ‘a serious will’ for the companies to create a strong European aerospace defence company.

The European Union cautioned that time was running out for Europe to remain a major player in the aerospace defence market.

New agendas need new visions

“Physicists are doing very, very well, ” says Richard Brook, sitting in the chief executive’s office at the Engineering and Physical Sciences Research Council. “We put more of our finance into physics departments than into any other. That’s an indication of the priority that we give to the subject.”

His statements will come as a surprise to many physicists. The EPSRC has cut the budget of its physics programme twice in the past three years and, although physicists receive almost as much money again from other EPSRC programmes, the overall trend is downwards.

Brook has been in charge of the council since it was set up four years ago and now controls a budget of more than £380m. He has made some notable reforms, particularly to the peer-review system, but to outsiders the EPSRC seems secretive, and the reasons behind the cuts to the physics programme remain mysterious.

Brook says that there are many justifications for the cuts. The one he mentions is that more than 50% of grant applications in physics are funded, compared with a success rate of only one in three in chemistry. Look elsewhere, however, and other reasons appear. An EPSRC newsletter says that the latest 3% cut was made because the physics programme “was not focused on new and burgeoning areas”. And in a letter to university vice-chancellors in February, Brook wrote that “concern for the physics programme has continued to centre on the extent to which former strengths can be sustained across a broad front without compromising opportunities to engage new fields”.

Stuart Ward, manager of the physics programme, is more direct. “There is a feeling that physicists generally are not as imaginative [as they could be]. They are not stretching the boundary of the field, and are not as innovative in their research [as they could be], ” he says.

In many ways the confusion over why the physics budget has been cut reflects a concern that the EPSRC is remote from most physicists. Individual researchers are occasionally asked to referee a research proposal, or to sit on one of the prioritization panels that decide which proposals should be funded, but senior researchers in particular feel that they can play little part in setting and formulating policy. There is, nevertheless, widespread praise among the physics community for Ward, and most physicists agree that he is doing the best possible job in the circumstances.

TOP, UP and physics

The EPSRC funds research in UK universities in eight programme areas that range from mathematics to engineering. It supports postdocs and postgraduate students, funds equipment, provides access to large facilities and runs various fellowship schemes. The council’s mission is to contribute to the UK’s economic competitiveness and to improve the quality of life. The physics programme is confined to mainstream areas of the subject, such as condensed matter, nuclear physics, and atomic, molecular, optical and plasma physics. Particle physicists and astronomers have their own research council.

Every autumn the EPSRC carries out a balance of programmes exercise, in which two high-level panels vote on whether the funding for each programme should go up, go down or stay the same. The Technical Opportunities Panel (TOP) looks at developments in individual research disciplines, while the Users’ Panel (UP) looks at the skills and expertise that the UK needs from the programmes. The EPSRC’s council then uses the votes and the panels’ comments to decide how much money each programme will receive. In 1996/7 the physics programme was given £24.4m to spend on grants and studentships (about 8.6% of the funds available), although physicists secured another £22.8m from other programmes, particularly from materials and information technology. An additional £17.7m went to facilities used by researchers who are funded by the physics programme (Physics World February pp22-23).

A great deal of power is vested in TOP and UP, and the way that these panels view different subjects can have long-term consequences for funding. The panels discuss each programme in turn but, in the end, the discussion boils down to a simple vote. Since the exercise began, physics and materials have regularly come in the bottom half of the voting, and funding for these programmes has suffered accordingly.

Subjective opinion also plays a big part. As Brook says, “[Physicists] have to persuade a group of scientists of high eminence who sit on our panels that physics justifies a substantial fraction of our budget.” However, it is not clear how they should do this. Brook rejected a proposal from the Institute of Physics, which publishes Physics World, that the EPSRC should set up a panel of physicists to help to draw up the information that is supplied to TOP and UP. He suggests that the physics programme should instead be reviewed by just one or two leading physicists, who should then propose a new direction for it. However, the reasons why TOP and UP voted in the way they did are shrouded in secrecy. The EPSRC refused to show Physics World a memo from TOP and UP to the council that summarized the panels’ views on physics. Brook admits that the EPSRC could improve the way it tells the community what the panels thought about each programme, but says that it is difficult to take a complex discussion from the panel meetings and encapsulate it in words. That cuts little ice with Mike Springford, head of physics at Bristol University. “To try to tell us that the arguments are so diffuse and subtle that they cannot be properly communicated is not acceptable, ” he says. Other physicists complain that the criticisms of the physics programme appear to change from year to year. In 1995 the programme was deemed to be poorly connected with industry. The following year it was said that physics was not exciting enough. Last year it was claimed that the programme lacked focus. Ring-fenced funding for nuclear physics was also identified as a problem (see ). Another inconsistency is that the programme received a positive report from an evaluation panel appointed by the EPSRC last year (Physics World October 1997 p57).

There are also concerns about the membership of TOP and UP. Of the 13 members of TOP, three are vice-chancellors and four are from just one institution: Cambridge University. “TOP is supposed to be made up of active researchers, but in my opinion it contains too many senior figures who are no longer at the cutting edge of research, ” says Mike Gunn, a condensed matter theorist from Birmingham University. He would prefer a greater number of younger researchers on the panel, who could spot exciting new areas as they emerge.

Other members of the physics community believe that it is the ex-physicists on the panels who are responsible for TOP and UP’s poor perceptions about the physics programme. However, David Wallace, a former theoretical physicist who is now vice-chancellor of Loughborough University and chairman of TOP, calls the balance of programmes exercise a “pretty impressive development”. He is proud of the way that the panel has worked and feels that the advice that it gives is not based on individuals pushing their own corner.

Peer review: reforming the system

One theme of Brook’s term of office has been his desire to reform the peer-review system. He is genuinely concerned that peer review should allow the most adventurous and speculative research to be funded. However, he is well aware that changing old procedures can alienate the research community. As he says: “We have to keep the community with us on this, because if it loses confidence in our peer-review system, our legitimacy is gone.”

In its early days the council abolished closing dates for grant applications, reducing the pressure on researchers to submit proposals that have not been fully thought through. Then it allowed researchers to suggest up to three potential referees for their grant applications. The EPSRC selects one of these referees, along with two experts from a college of about 120 physicists, to review the application. And recently, all of the young researchers who hold advanced fellowships have been appointed to the college to ensure that, as Brook puts it, “the doors are open to people at the beginning of their careers”.

Although a recent survey by the Institute of Physics found that there was no widespread dissatisfaction with the quality of the EPSRC’s refereeing, there is still room for improvement. One problem is that just 2% of proposals to the physics programme are rejected by referees. Many physicists therefore receive a positive referee’s report, only to find that their application is then turned down by the prioritization panel. Ward says that one of his most difficult tasks is explaining to unhappy physicists why their application has not been funded.

The prioritization panel consists of about 12 physicists drawn from all areas of the subject, and meets about four times a year. It orders the proposals on a scale of one to five, based on the quality of the research proposed and the referees’ comments. Ward and the panel chairman then decide how many proposals on the list can be funded, starting from the top. Funds for the seven different themes of the physics programme are not earmarked – the aim is that the best applications should get funded, whatever field of physics they are from.

However, some physicists say that there is a danger in this approach: without guaranteed funding for different areas of physics, valuable parts of the subject could simply wither away through neglect. Another problem is that the physicists on the panel have to judge proposals from all areas of physics. As Mike Gunn from Birmingham says, this may be unfair on applicants who are less well known or who are working in new fields. Having served on the physics panel, he wonders if it should be split up into subdisciplines, each of which would be able to judge applications more carefully.

However, Julian Jones, an optical physicist from Heriot-Watt University who has sat on many prioritization panels, disagrees. Jones, who is also a member of TOP, points out that a single panel has the advantage that a single quality standard can be applied across the whole programme.

Other physicists criticize the EPSRC’s peer-review system for forcing researchers to specify who will benefit from their work. For physicists doing basic research, the beneficiaries are often other academics. But Gordon Davis, head of physics at King’s College London, feels that physicists can find it hard to specify how their work will benefit industry, particularly in the long term. He says that many physicists end up trying to use a lot of buzz words in proposals, even when they feel they shouldn’t. “It’s perhaps easier for other scientists to talk about research that industry might take up, ” he says. “Maybe physicists should just be more extrovert.” So what should physicists do? “I think the answer is obvious, ” says Ward. “They should be putting forward proposals that are more speculative, addressing broader questions in physics and taking steps to ensure that others who could benefit from knowledge that they are developing are informed about it.” He argues that having a working relationship with industry is no impediment to performing leading-edge research, and says that incremental proposals will in future have to compete hard to be funded. “At the moment [the physics programme] has a mass of research in the middle, with not enough at the highly innovative end and not enough at the industrial end.”

However, one physicist, who does not want to be named for fear of jeopardizing the chance of being funded, feels that programme managers have too much influence. “If you don’t have their support, you won’t get funded. I’m absolutely unequivocal about that, ” he says. This researcher also claims that grant proposals from physicists working in the more applied areas that Ward refers to are often sent out to other programmes, such as materials, IT and engineering, which evaluate proposals using different criteria.

Jean-Patrick Connerade, an atomic physicist at Imperial College, London, also criticizes programme managers for not being experts in their subject. He feels that it would be better if expert programme managers were seconded from the research community, as happens in the US.

Be bold and brave

So what is the EPSRC’s message to the physics community? Brook says that the vital importance of physics needs to be encapsulated in such a way that those who work outside the field find it to be compelling. However, he is open to persuasion. “Where [physicists] have concerns, they should advise us, and they’ll find that we are very willing to enter into full debate about it to make sure that we get the best programmes in the future, ” he says. Physicists will get their first chance at a number of discussion meetings between the community and the EPSRC later this month. A meeting is also being organized to gather the views of younger researchers on the physics programme. As for Ward, he would like leading researchers to have the courage to change field or to address new topics within their own field. “Don’t focus on the EPSRC but on what physics can offer, on what challenges it can address and what solutions it can offer society. Get that right and everything else will follow. The challenge [for physicists] is to reinvent themselves and ensure that physics is addressing the really important questions. The people who have the vision, the invention and the skills are the physicists.”

Researching the Web

On page 98 of the April 3 issue of Science Steve Lawrence and Lee Giles of the NEC Research Institute in Princeton, New Jersey, report that no search engine covers more that one third of the 320 million indexable pages on the Web. The pair studied six search engines and found that HotBot covered the highest number of indexed pages (34% of the total), while Lycos covered the least (3%). However, HotBot also had the highest per centage of ‘dead links’ with 5.3% of the links not leading to the correct page. The average number of dead links on all engines was 3.1%.

Lawrence and Giles suggest that the best way to search the Internet is to use a search engine that combines output from a number of engines, such as Metacrawler. However, to look for a individual’s homepage, a ‘softbot’ – a program such as AHOY that can intelligently sort search data into a more meaningful structure – was recommended.

On page 95 of the same issue Bernardo Huberman and colleagues at the Xerox Palo Alto Research Center in Palo Alto, California, found that users follow common patterns of behaviour when looking at Web sites. The team constructed a model that matched an ‘interest’ threshold to the number of pages a user would look at, and tested it by studying the Web behaviour of 23, 692 America Online users over a total of five different days. They discovered – just as their model predicted – that on average a user only looks at three pages on a Web site, with most users looking at only one page. Part of the reason for this low number could be the slow access speeds available to most American Online members. The model does not work (yet) to predict the behaviour of individual communities such as physicists.

A tale of two councils

Two of the acronyms most frequently used by physicists in the UK celebrate their fourth birthdays this month. Between them the EPSRC and PPARC fund most of the research projects performed by physicists in UK universities. The remit of the Particle Physics and Astronomy Research Council (PPARC) is self-explanatory, while the Engineering and Physical Sciences Research Council (EPSRC) supports most other areas of physics, with a few exceptions such as biophysics. The two councils have approached their tasks in very different ways and with varying degrees of success. In this month’s Physics World Ken Pounds, the outgoing chief executive of PPARC, describes how crisis management often had to take priority over scientific leadership. Sometimes this was caused by circumstances outside of his control, mainly fluctuations in subscriptions to international bodies such as CERN and the European Space Agency. A related problem was the fact that the council’s domestic budget – effectively the money it has to support experiments that use facilities it has already paid for – was falling in real terms, while the scientific opportunities open to particle physicists and astronomers were multiplying. This continues to be a problem.

After a sometimes torrid spell in office – the council supports the work of two vigorous, well organized and vocal communities – Pounds and PPARC have recently been able to devote more time to scientific leadership. A major challenge for Pound’s successor, Ian Halliday, will be to convince the government that the science in PPARC’s “road map” is just too exciting and too important not to be funded properly. Halliday has also identified two other priorities: career structure for postgrads and postdocs, and the need to take more risks in research.

What chance success? The UK’s new science minister, John Battle, has already visited CERN and the UK’s dark matter experiment, and seems to have been impressed by both. It is to be hoped that this, coupled with Battle’s enthusiasm for science that appeals to the public imagination – and PPARC’s certainly does – will bode well for particle physics and astronomy in the UK. The EPSRC is a very different beast. It currently funds researchers working on everything from the theory of Bose-Einstein condensates to engineering for manufacturing. In addition it is also expected to fund research that will lead to the creation of wealth, and to have closer links with industry than PPARC. Physicists still receive more from the council than their colleagues in other departments, but the gap is narrowing. And although many physicists are quick to criticize the council in private, they are reluctant to do so on the record.

There are contradictions at the council as well. Policy seems largely to be dictated by two panels – buoyantly called TOP and UP – but these panels seem to operate like black boxes, a process that is sure to intrigue and infuriate curious physicists. Moreover, it is obvious that these panels have a low opinion of the council’s physics programme. Yet when the EPSRC set up evaluation panels to look at the quality of the research that it funds, large parts of the physics programme were found to be world leading. There is no doubt, however, that the council wants to see the programme move in new directions, and physicists would be foolish to ignore strong hints about the need for more innovative ideas and better links with industry. Whether the best way to achieve this is the way suggested by the council’s chief executive – a new direction drawn up by one or two leading physicists – is less clear. Such an approach might serve a university department rethinking its priorities but is ill-suited to a community of hundreds of researchers across more than 40 universities.

The EPSRC also takes a dim view of the breadth of the current physics programme. But surely this breadth is a good thing. By all means cut those areas where there is only scope or hope of incremental progress, but given that the programme does not include particle physics, astronomy and many areas linked to electronics and optics, there is little need to focus further. Indeed, the message from both sides – the council and the researchers – seems to be that the other side could do better.

Chaos starts to communicate

Gregory VanWiggeren and Rajarshi Roy of the Georgia Institute of Technology in the US have now used chaotic lasers to generate the complex signals of the type needed in many of today’s communications systems (G D Van Wiggeren and R Roy 1998 Science 279 1198). The chaotic laser system can be used to synchronize a transmitter and receiver, and to transmit encrypted data.

So what made optical scientists decide to exploit, rather than prevent, chaos in lasers? To understand this goal, we must first recognize that chaos can be useful. Although the dynamics of chaotic systems are continually unstable, they are also bounded. This causes the variables in the system to oscillate in a noisy but deterministic way. It is therefore difficult – or in some cases impossible – to predict the future states of the system.

The result is that the signals produced by a chaotic system are highly complex and contain a broad range of frequencies. Such signals are similar to those used in “spread-spectrum” communications and related fields, in which information is hidden within noisy signals. Current methods for generating chaotic signals generally use simple electrical circuitry to create the background noise, but it is difficult to push the circuitry to the high frequencies needed for many communication channels. But a physical system, such as a laser, produces the noise automatically.

The potential of chaotic signals in communications was first investigated in 1990, when Thomas Carroll and I at the US Naval Research Laboratory used chaotic circuitry to synchronize transmitters and receivers, and to send hidden or encrypted messages. In 1993 Kevin Cuomo and Alan Oppenheim of the Massachusetts Institute of Technology published the first details of a successful transmitter-receiver circuit.

There have been two main problems with this approach. First, most of the circuitry has been in the audio range or just above, which limits the rate at which messages can be transmitted to between 0 and 10 kHz. In principle, there is no reason why radio-frequency (rf) circuitry should not be used, with frequencies in the megahertz or even gigahertz range, but this would add an extra element of complexity.

Another problem is that almost all of the chaotic systems used so far have been low-dimensional. In other words, the number of variables needed to describe the system, such as currents and voltages, have been less than 10, and often less than 5. Many communications schemes require more complex signals with higher dimensions.

The chaotic laser system developed by VanWiggeren and Roy overcomes both of these problems. The chaotic signals from the system are around 100 MHz, which yields a data rate comparable with that used in rf communications. Perhaps more importantly, the method used to generate the chaos in the laser system can lead to high-dimension laser dynamics. The actual dimension is not yet accurately known, but it could be 50 or more. Mathew Kennel and Henry Abarbanel of the University of California at San Diego (UCSD), who originally showed that such a laser system could be used for synchronization, are now calculating the dimension of the system.

At the heart of the laser system is a transmitter consisting of a ring laser made from erbium-doped fibre. An optical signal is generated by an erbium-doped fibre amplifier (EDFA), and is reinjected into the EDFA after circling the ring once. This means that the laser is driven by its own output but at some time delay, which leads to chaotic and high-dimensional behaviour. This type of response is common to time-delayed dynamical systems of any kind.

The message to be transmitted is converted into an optical signal with another EDFA. This optical information is coupled into the fibre ring of the transmitter, and is injected into the laser together with the time-delayed laser signal. This means that the information signal also drives the laser and so becomes mixed with the dynamics of the whole transmitter. Such an information-dynamical mixing technique was first suggested by Alexander Volkovskii and Nikolai Rulkov at UCSD.

As the combined information/laser signal travels around the transmitter ring, part of it is extracted and transmitted to the receiver. At the receiver the signal is split into two. One part is fed into an EDFA almost identical to the one in the transmitter, which ensures that the signal is synchronized with the dynamics of the ring-fibre laser in the transmitter. It is then converted into an electrical signal by a photodiode, providing a duplicate of the pure laser signal at some time delay. The other part is fed directly into another photodiode, which provides a duplicate of the laser-plus-information signal. After taking account of the time delays, the chaotic laser signal can be subtracted from the signal containing the information, removing the chaos and leaving the initial message.

The information signal in this experiment was kept simple – a pure square wave with a period of about 100 ns. No structure is observed when the transmitted signal is plotted in three-dimensional phase space, consistent with the high-dimensional nature of the chaos. The signal recovered by the receiver matches the transmitted signal reasonably well. Although the extracted signal does not reproduce the fine structure, the receiver can easily detect the 1s or 0s in a typical digital signal.

Several issues need to be resolved before such laser systems can be engineered into communications systems. The first is the information rate. Although these experiments have proved that data rates in the rf range can be achieved, higher data rates will be needed to compete with current communication schemes. In more recent work, the researchers have increased the information rate to 150 MHz.

The main bottleneck seems to be the use of electro-optical components to convert optical signals to electrical ones. If all of the signal processing could be performed optically, with no limitation set by the detection electronics, the technique would only be constrained by the dynamics of the laser system. In principle, the method could be extended into at least the gigahertz range.

Another problem with simply adding a chaotic signal to the information is that it is possible to identify information signals with a distinctive frequency content. For example, the periodic square wave used in the experiments appears as a spike in the spectrum of the transmitted signal. An intruder would be able to filter this frequency and isolate the information signal, although some typical filters applied by VanWiggeren and Roy were unable to achieve this. This problem could be overcome by mixing the information and chaos in some nonlinear way, and the researchers say that some work with nonlinear mixing has been successful. This work is sure to continue.

Despite the remaining problems, the experiments show that physically chaotic systems, rather than chaotic circuits, could overcome the problems that have stymied researchers and engineers in this field. Indeed, this might be the best message of this new research. Many materials and optical systems are nonlinear and can display chaotic behaviour, suggesting that an abundance of chaotic sources are available. The only problem is finding suitable chaotic systems, and VanWiggeren and Roy have provided us with an impetus to do just that.

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