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Why does Africa need the Square Kilometre Array? August 16, 2011

Posted by admin in : Astronomy and Astrophysics (ASTRO), Cosmology, Gravitation, and Relativity (CGR), History, Policy and Education (HPE), Technology Transfer, Business Development and Entrepreneurism (TBE) , 2comments

2009 Address by Dr Adrian Tiplady, Manager, Site Characterization, SKA Africa Project Office

Honourable Minister, distinguished guests, ladies and gentleman

Why does Africa need the Square Kilometre Array? It is a question often posed by a public that is cognisant of the many high priorities that South Africa, and Africa as a whole, faces. We are currently engaged in an international race, competing to host a multi‐billion dollar, cutting edge astronomical facility that, in my view, may very well be mankind’s last great astronomical adventure still bound on earth. Do we, as South Africans, have the skills and expertise to compete within the world’s scientific community, to produce scientists and engineers of the highest calibre that will compete in the global knowledge economy? (answer at the end)

Today, during the International Year of Astronomy, the world faces economic recession and a financial crisis like never before. Uncertainties in food, water and energy supply loom, whilst climate change has become an ever present maxim in the implementation of global policies. Africa suffers from the unrelenting scourge of preventable diseases such as Aids and malaria. Why, then, has South Africa, and Africa, announced to the international community that “we have the desire to become the international hub for astronomy”?

In the US, President Barak Obama has committed to significantly increasing investment into science, as one of the most important parts of stimulating the economy. In his address to the US National Academy of Science, President Obama said:

“At such a difficult moment, there are those who say we cannot afford to invest in science, that support for research is somehow a luxury at moments defined by necessities. I fundamentally disagree. Science is more important for our prosperity, our security, our health, our environment and our quality of life than ever before”.

He went on to say:

“The pursuit of discovery half a century ago fueled our prosperity … in the half century that followed. The commitment I am making today will fuel our success for another fifty years. That’s how we will ensure that our children and their children will look back on this generation’s work as that which defined the progress and delivered the prosperity of the 21st century. …. The fact is that an investigation into a particular physical, chemical or biological process may not pay off for a year or two, or a decade, or not at all. But when it does, the rewards are often broadly shared……..And that’s why …… the public sector must invest in this kind of research – because while the risks may be large, so are the rewards for our economy and our society. ….. It was basic research in … the photoelectric effect that would one day lead to solar panels. It was basic research in physics that would eventually produce the CAT scan. The calculations of today’s GPS satellites are based on the equations that Einstein put on paper more than a century ago”.

Even with the wealth disparity between the USA and South Africa, science and technology on the African continent is still seen as key to our ability to solve the problems of development that will determine the future of Africa and South Africa. Investment in mega‐science facilities has never been as important as it is today, where the brain drain, ill equipped school leavers and the lack of funding for higher education facilities to pursue areas of basic research have a directly detrimental effect on our ability to participate in the global knowledge economy, where we become innovators as opposed to consumers of technology.. And to retain these people, to stem the flow of skilled people leaving these shores, we need to provide flagship projects, such as those in astronomy that places cutting edge development in a variety of scientific and engineering disciplines at its core competency.

In 2003, the Department of Science and Technology and the National Research Foundation decided to enter into a race with four competing countries to host the world’s largest radio telescope. The Square Kilometre Array, as it is known, began as an international project in 1991, and currently involves 55 institutions across 19 countries. At a capital cost of more than $2 billion USD, the international consortium aims to have the SKA up and running by 2022, spending a further $150 million USD per year for the next 50 years in running costs. Much of this expenditure will be spent in the host country. The instrument is projected to be between 50 and 100 times more powerful than any radio astronomy facility ever built, an array of some 4,500 radio telescopes distributed over an area 3,000 km in extent. Combining the signals from each of these telescopes using a supercomputer 100 times more powerful than anything that exists today will create a virtual telescope, spanning 3000km in diameter, with a total collecting area of 1 square kilometre ‐ the equivalent of over 1,000,000 DSTV satellite dishes. This will result in an instrument with unparalleled sensitivity and resolution.

In this International Year of Astronomy, we believe we understand just 4% of all the matter and energy in the universe. The world’s astronomical community are striving to answer some of the great fundamental questions that face the world’s scientific community, and also raise new questions ‐ not just in astronomy but indeed in fundamental physics. Instruments such as the recently launched Herschel and Planck telescopes are being put into orbit 1.5 million km away from earth, collecting the kind of data that is possible now because of technological innovations in the last 10 years. Data that could help us answer the very mysteries of the universe. Plans are afoot to venture outside of the earth, and even place telescopes onto the dark side of the moon.

The SKA is part of this frontier of new instruments. Some of the many questions to be answered are :

What is the nature of dark energy – a mysterious force that acts in opposition to gravity on very large distances, repelling massive objects from each other with ever increasing force?

How did the universe and all that is contained within it evolve – radio signals have been travelling through the universe for 13 billion years, and we are only receiving some of them today as we take “pictures” of the big bang and the first stars and galaxies. We will be able to make snapshots of the universe through time.

Mankind has long striven to answer the question of whether there is life on other planets? The detection of biomolecules, or even artificial radio transmissions, may answer this. These questions and more, however, probably do not approach the rich rewards that will come from not what we plan to investigate, but rather what we haven’t planned for. Radio telescopes today are not remembered for what they were built, but instead for what they serendipitously discovered.

When South Africa, with a rather small human capital base in radio astronomy at the time, submitted its bid in 2005, we took the international community by surprise. Any degree of afro‐pessimism was dismissed, however, when South Africa was shortlisted along with radio astronomy international heavyweight ‐ Australia. Why? Because we have something that no amount of financial investment could ever buy. We have one of the best locations in the world to build and operate astronomical facilities, and a very committed Department of Science and Technology and National Treasury.

The Southern African Large Telescope in Sutherland has some of the darkest skies in the world – and the proposed SKA core site, just 80km northwest of the town of Carnarvon in the Northern Cape, has one of the best radio frequency environments in the world, free from a majority of the interfering radio signals that plague most of the world’s radio astronomy facilities. Furthermore, because of our geographic location on the planet, the very best astronomical sources to observe pass right overhead – we literally have the best window on the planet out of which to gaze upon the universe, and explore the centre of the Milky Way Galaxy.

Protection of this site is of the utmost importance – not only to protect South Africa’s geographical advantage, but to preserve the site for the world’s astronomical community. To meet this requirement, the Department of Science and Technology has promulgated the Astronomy Geographic Advantage Act, which allows for the establishment of an astronomy reserve in the Northern Cape Province. A reserve in which astronomy facilities are protected from sources of optical and radio interference.

The Australian Minister of Science has described winning the SKA bid as being like winning the Olympic site bid every day for 50 years. If the right to host the SKA were to be awarded to South Africa, and its 7 African partner countries, we would become a premier centre for research in astronomy and fundamental physics – going hand in hand with cutting edge development in the engineering technologies that co‐exist with this field of research.

As many of the technologies do not yet exist, to build the SKA will require a significant international effort in the fields of information and communication technology, supercomputing, mechanical, radio frequency, software and electronic engineering, physics, mathematics and, of course, astronomy. All fields that provide a basis for a strong knowledge economy. In 2004 the DST, together with the NRF, decided that simply competing to host the SKA would not meet the aims of building a knowledge economy – what was needed was a flagship project that would provide an opportunity to increase the skills base of our young scientists and engineers. We needed to participate in the technology development for the SKA, to grow a substantial base of scientists and engineers in South Africa that would be able to use, operate and maintain the SKA. And so was born the Karoo Array Telescope – an SKA science and technology pathfinder.

MeerKAT, as it is now known, will be the first radio interferometer built for astronomical purposes in South Africa. It will consist of 80 dishes, and once completed in 2013 will be one of the world’s premier radio astronomy facilities that will have not only South Africa scientists, but the world’s astronomical community, clamouring to use – 9 years before the SKA is scheduled to be commissioned.

Over the course of the last 5 years, we have built up a team of some 60 young scientists and engineers who are working on the technologies and algorithms required for the MeerKAT, which will in turn test the technologies for the SKA. Many of these people would have most probably left these shores already, looking for more exciting projects to work on in Silicon Valley, or other technology clusters. However, the lure and attraction of such a project as MeerKAT, and the larger SKA, has kept them here. Although none had any radio astronomy training, the team has quickly become an international leader in the development of technologies for radio astronomy facilities, which in fact are the generic technologies upon which the digital age depends, and are highly likely over many years to generate spin‐off technologies, innovations and patents. They have managed to do this through international collaboration with institutions such as Oxford, Cambridge, Manchester, Caltech, Cornell and Berkeley, as well as the national radio astronomy observatories in the USA, India, Italy and The Netherlands. We are also working closely with several South African universities and companies.

Amongst other things, the team has developed the first every radio telescope made from composite materials, and is playing a leading role in the international development of digital hardware for real time data processing. The first 7 MeerKAT dishes are being constructed as I speak.

In a recent editorial in the local WattNow magazine, Paddy Hartdegen says the following of the SKA and MeerKAT projects : “In my view, gee whiz projects such as the SKA and the MeerKAT go a long way to encouraging youngsters to take science and engineering disciplines more seriously. And if there is some thrill attached to science, astronomy or mathematics, then the students will apply themselves more diligently at primary and secondary schools, to ensure that they will have the necessary qualification to enter a university”. He goes on to say “I believe that projects such as the SKA can actually foster the sort of compelling interest that is reserved for sports stars and pop musicians“

So, is Paddy Hartdegen right? Do the SKA and MeerKAT projects have the qualities that will attract students into science, engineering and technology? In 2005, we initiated a Youth into Science and Engineering program, to rapidly grow the human capital base in astronomy and engineering in South Africa. To date, we have awarded 142 post‐doctoral fellowships, PhD, masters degree, honours degree and undergraduate degree bursaries. We are currently awarding approximately 45 bursaries per year. We are assisting universities to increase their astronomy research capacity, and to develop additional capacity to supervise students through international supervisory programs. The question is, can these students stand on their own two feet within the international astronomical community?

For the last 3 years, we have held a post‐graduate student conference for our bursary holders, where each student presents the results of his or her research. We invite a number of international experts to attend. To date, none have declined the invitation – not due to the opportunity for a holiday in Cape Town, but instead because of the astounding reputation this conference has grown internationally due to the quality of students and research. Professor Steve Rawlings, Head of Astrophysics at Oxford University, said on his departure “I am awfully impressed by what I have seen at this conference and how things have exploded on the science and engineering side on such a short timescale. South Africa is doing all the right things for the SKA”.

So, what has the establishment of a flagship project resulted in? People. Skilled people. The new measure of financial prosperity. Skilled people who are helping to change South Africa’s reputation as a place of high technology investment, research and development. These students, who cross the race and gender lines, may never stay within the field. However, they will carry the skills they have learnt into new areas, and their impact will be felt through a variety of socio‐economic lines.

The SKA, and the MeerKAT, has matured into a project of which we, as the South African scientific community, can be proud. It is a project that should capture the South African public’s imagination, young and old alike.

Do we, as South Africans, have the skills and expertise to compete within the world’s scientific community, to produce scientists and engineers of the highest calibre that will compete in the global knowledge economy?

We have in the past, and we will continue to do so. The answer, therefore, is a resounding yes.

Southern Africa’s SKA Bid: A Worthwhile Investment June 14, 2011

Posted by admin in : Astronomy and Astrophysics (ASTRO), History, Policy and Education (HPE), Technology Transfer, Business Development and Entrepreneurism (TBE) , add a comment

By Congressman Bobby Rush

Southern Africa is quickly establishing itself as a hub for astronomy, scientific expertise and in doing so, is creating an unrivalled opportunity for the development of skills and expertise that will allow Africa and its people to be significant contributors to the global knowledge economy.

In 2012, a consortium of major international science funding agencies will select a location to house the world’s most powerful radio telescope, The Square Kilometre Array (SKA). The SKA promises to revolutionize science by answering some of the most fundamental questions that remain about the origin, nature and evolution of the universe. With about 3 000 receptors linked together and a total collecting area of one square kilometre, the SKA will have 50 times the sensitivity and 10,000 times the survey speed of the best current-day radio telescopes. The SKA will enable scientists to gain insight into the origins of the universe and provide answers to fundamental questions in astronomy and physics.

Currently, two locations are under consideration: Africa, under the leadership of South Africa, and Australia/New Zealand, under the leadership of Australia. South Africa’s SKA bid proposes that the core of the telescope be located in the Northern Cape Province, with additional antenna stations in Namibia, Botswana, Kenya, Mozambique, Madagascar, Mauritius, Ghana and Zambia.

South Africa has already demonstrated its excellent science and engineering skills by designing and starting to build the MeerKAT telescope, an SKA precursor telescope. Five years before MeerKAT becomes operational, more than 43,000 hours of observing time have already been allocated to radio astronomers from Africa and around the world, who have applied for time to do research with this unique and world-leading instrument. US astronomers are leading some of these research teams.

There is already active collaboration between the South Africans and UC Berkeley, the National Radio Astronomy Observatory and Caltech on the PAPER and CBASS telescopes respectively, which are currently hosted on the South African radio astronomy reserve. Collaboration is also taking place between these US research institutions and the MeerKAT team on the development of technologies for the MeerKAT and US telescopes.

The SKA in Southern Africa represents an unrivalled opportunity to transform Africa through science and technology by driving the world’s best and brightest to the region, and providing the continent’s youth with a world-class incentive to study science and provide the world answers to the planet’s oldest questions.

The SKA in Southern Africa will create a critical mass of young people in Africa with world-class expertise in technologies that will be paramount in the global economy in the coming years. New technologies, scientific discoveries and infrastructure development taking place in Africa will contribute to the creation of entirely new industries and spur development in many fields of human endeavor, while transforming Africa as a major hub for science in the world and creating a new continent of opportunity for American business to cultivate and develop partnerships throughout Africa.

The construction of major science infrastructure in Southern Africa, such as the $2 billion SKA project, will also represents an important opportunity for U.S. business to cultivate and develop partnerships in the region that can lead to new technologies, new industries and economic development both here in the USA and throughout Africa.

The SKA represents a unique opportunity to accelerate the development of skills and expertise that will allow Africa and its people to be significant contributors to the global knowledge economy. We should support southern Africa in its quest to become contributors to global science and equal partners in the knowledge economy.

Bobby Rush is the U.S. Representative for Illinois’s 1st congressional district, serving since 1993. He is a member of the Democratic Party. A long-time advocate of increased trade with Africa, he has introduced H.R. 656, the African Investment and Diaspora Act, to advance the mutual interests of the United States and Africa with respect to the promotion of trade and investment and the advancement of socioeconomic development and opportunity.

The US remains supportive of the Square Kilometer Array project April 7, 2011

Posted by admin in : Astronomy and Astrophysics (ASTRO), History, Policy and Education (HPE), Technology Transfer, Business Development and Entrepreneurism (TBE) , 1 comment so far

Though the United States did not officially join the Founding Board of the Square Kilometer Array (SKA), the US does remain supportive of the project. In large part, the decision not to join the Founding Board is based on the recommendations of the most recent astronomy decadal survey performed by the National Research Council, “New Worlds, New Horizons in Astronomy and Astrophysics,” released in August 2010. This report concluded that the combination of technical readiness and high cost risk made it unfeasible for the National Science Foundation (NSF) to invest in SKA construction during the 2010-2020 decade. NSF has accepted that conclusion and is setting a priority for SKA construction that is consistent with this conclusion and the other recommendations of the decadal survey.

NSF has invested in SKA technology development and in several radio telescopes that serve as scientific and technical pathfinders for the SKA, as well as pursuing some of the science goals envisioned for the international SKA, and will continue to make such investments as funds and independent reviews permit.

The SKA is an exciting project for astronomy. It was originally conceived as a focused project to study the end of the “Dark Ages” – the time when the first stars, black holes, quasars, and other high energy objects formed, ionizing the almost 100% neutral hydrogen gas left around from the Big Bang. You can imagine the universe at say z=20 being dark and transparent. But as the ultraviolet light begins to come from the first sources, the light ionizes larger and larger regions of the Universe – sort of like Swiss Cheese until redshift around z=6 where most of the hydrogen is ionized as it is today.

The SKA will slice through this redshift range giving us an accurate tomographic image of the Universe as it begins to form the elements of the periodic table, and begins to form the seeds of what we now see are galaxies and massive black holes. Its science case has expanded since then, but the main focus of the science is the tomography of the early Universe.

But the final SKA design is far from certain. Technology is still in development, and the final cost of the SKA is quite unknown. It may turn out actually that the SKA evolves to be three very large telescope arrays that are not co-located. A major factor of the SKA to site in a region free from FM carrier frequencies, and there are remarkably few in the world. Among them are sites selected in Africa and in Australia.

No definitive scientific rationale has emerged to favor the African site over the Australian or vice versa. Each project is pursuing pathfinder telescopes as pre-cursors to the SKA, and each is molded better to different capabilities.

But there may be international policy issues that would motivate the US to help fund the project now. The US presently supports, and will build, new major telescopes in Chile, including the LSST, CCAT, and ALMA the latter being an international collaboration. Chile has benefited greatly by hosting these telescopes, not only in building astronomy programs, but through other spill-over effects, e.g., broadband connectivity, service sector jobs and growth in the knowledge-based innovation economy. During President Obama’s recent trip to Chile, he and President Pinera issued a joint communique that they recognized the close historical collaboration in astronomy between the two countries and looked forward to future projects.

There are scientists and policy makers that would like to see an astronomy-catalyzed economic transformation in Africa. South Africa already has a long and distinguished history in astronomy research. Astronomers are developing academic programs and research telescopes in Botswana, Burkina Faso, Ethiopia, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia, Nigeria, Zambia, and others. Last December African astronomers organized the African Astronomical Society to be the voice of the astronomy profession on the continent and to be the continental interlocutor with other astronomy professional societies around the world. The SKA is a tremendous opportunity to help develop astronomy in Africa. If the Chilean example is a guide, the SKA would help develop high-tech industry and build a larger community of African astronomers, physicists, and engineers.

But the results of the decadal survey stunts the rationale for large-scale US investment (and for the US that means NSF funding) in the SKA, at least for this decade. This is probably the right choice. There are other projects, e.g., WFIRST, LSST, where the technology is more mature and thus closer to fruition. As the US faces limited fiscal options the decadal survey is the accepted process for the field to make hard decisions. Without a determined technology for SKA there is no way to make any firm cost determinations. So the question of whether to support the SKA long-term remains open.

But all is not lost for this decade. The South African MeerKAT and Australian ASKAP, both of which will be completed in this decade, will be extremely powerful telescopes. The MeerKAT in particular will be well-suited for pulsar timing studies that can reveal much about relativity, gravitational lensing, and nuclear physics.

Maybe this decade will see investments from other functions of the federal budget, e.g., foreign assistance through the State Department. Maybe the foreign assistance budgets of other donor countries can be brought to bear on the SKA project. After all, the total budget for the SKA construction is actually quite small compared to the total amount pledged by the G20 nations for development in Africa. Maybe the US Commerce Department, other nations’ ministries of industry, and private corporations will view the SKA as a technology incubator and thus find funds to help with technology development. And maybe philanthropists will find the SKA worthy of their donor dollars.

What remains true is that in Africa the SKA project has a full head of steam. South African science minister, Naledi Pandor, has said, “I am intent on ensuring that South Africa wins the bid to host the Square Kilometer Array radio telescope” and “…[I am] …not going to entertain any matter that might distract me from achieving that goal.” The Heads of State of the African Union have endorsed the African bid for the SKA telescope, signaling multilateral cooperation at the highest levels for this project.

The African SKA project team has already achieved impressive results with their KAT-7 precursor telescope, as well as in electronic design, manufacturing and logistics. And the SKA Project Office has conceived and developed the extremely clever idea of an African VLBI network that would use decommissioned communications dishes across the continent. Five years before South Africa’s MeerKAT telescope becomes operational, more than 43,000 hours of observing time (adding up to about five years) have already been allocated to radio astronomers from Africa and around the world.

The SKA human capacity development program is already an unqualified success. The challenge is to keep the steam chest full and to build on all these successes. The National Society of Black Physicists will of course maintain its collaborations with the African astronomy community. In addition to producing outstanding astronomy research results, we believe the African SKA will lead to the creation of an African scientific technological base that will in turn act as the engine of African economic development and will transform the African economy to one that is more based on knowledge, connectivity, technology and innovation. As an international research center located in Africa, the SKA will help unbridle the imaginations of young Africans and inspire them to pursue math and science at school, and to follow careers in science and engineering. This would create a critical mass of problem solving thinkers, able to find solutions to the water, food, health, energy and environmental challenges of the continent.

Industrial Masters and Internship Program at University of Oregon February 26, 2011

Posted by admin in : Chemical and Biological Physics (CBP), Condensed Matter and Materials Physics (CMMP), History, Policy and Education (HPE), Photonics and Optics (POP), Technology Transfer, Business Development and Entrepreneurism (TBE) , add a comment

You can earn a Masters degree and a salary one year through the University of Oregon’s Masters Industrial Internship Program. This program provides students with the real-world knowledge and skills necessary to be successful in an industrial environment.

The best way to judge the success of the Industrial Masters Program may be its history and its list of corporate partners. Over the last 13 years, approximately 90% of the students that have completed internships through this program have received offers for regular employment from their host company. We also have an impressive group of corporate partners such as Nike, Intel, IBM, Fairchild Semiconductor, Hewlett Packard, the Army Research Lab, ESI, Nanometrics, FEI Company, nLight, DataLogic and SolarWorld.

Through this program students have the opportunity to earn a degree from a leading research university and also learn what is required to be successful after graduation. We focus on the science and help you develop professional business skills that will allow you to be successful throughout your career.

The course work and labs are designed to help students become more effective problem solvers and will assist in developing your communication, collaboration and leadership skills. The labs are built to give students an opportunity to have experiences that closely mirror those they’ll find in industry.

The UO’s Masters Industrial Internship Program awards MS degrees in Chemistry or Applied Physics. Students entering the program typically have bachelor degrees in one of the following areas: Chemistry, Biochemistry, Physics, Chemical Engineering, Mechanical Engineering, or Electrical Engineering.

You can choose to focus in one of four core areas:

• Photovoltaic & Semiconductor Device Processing

• Optical Materials & Devices

• Polymers & Coatings

• Organic Synthesis & Organometallics

Internships/co-ops typically pay from $2,400 – $5,400 per month. Though internships are not guaranteed, the program has historically placed 98% of its students in internships and the program staff assists in every way to ensure you are a very competitive candidate for available opportunities.

To find out more please visit: internship.uoregon.edu

We are excited to talk to you about the program and life in Oregon–and to help you plan a visit to campus. The University of Oregon is located in Eugene in Oregon’s Willamette Valley. We’re a short drive from the Pacific Ocean, the Cascade Mountains and a two hour drive from Portland – the second largest city in the Pacific Northwest.

For more information:

Lynde Ritzow, Associate Director Masters Industrial Internship Program

T: (541) 346-6835

E: lynde@uoregon.edu

W: internship.uoregon.edu

Semiconductor laser diode produces stabilized optical frequency combs for telecommunications, metrology, signal processing and spectroscopy. October 22, 2010

Posted by POP Section Chair in : Photonics and Optics (POP), Technology Transfer, Business Development and Entrepreneurism (TBE) , add a comment

by Dr. Peter J. Delfyett, President, National Society of Black Physicists and University Trustee Chair Professor of Optics, ECE & Physics

A novel approach to generating a stabilized, phase-locked and coherent set of peri­odic optical frequency combs enables researchers to develop these sources at a frac­tion of the cost of conventional solid state and fiber based sources and thus facilitates their use in a broad range of information, sensing and measurement applications.

The use of lasers in communications, signal processing, test and measurement systems and spectroscopy has enabled many key advances over the past decades owing to the wide range of useful characteristics that accompany coherent laser radiation. Further advances are envisioned by using multiple lasers, each with differing wavelengths that allow parallel optical channels to increase the measure­ment and processing capability. Additional functionality is enabled if each op­tical frequency channel is phase-locked to the other optical channels, i.e., if the relative phase relation between each wavelength channel is well established and fixed and not drifting over long times [1]. To achieve a set of frequency combs with a fixed phase relation, one can use a single continuous wave (cw) laser and modulation techniques such as amplitude or phase modulation to create sidebands [2]. Further channels can be added through nonlinear optical interactions such as four wave mixing. In this approach, the characteristics of the optical frequen­cy comb, such as frequency stability and linewidth, is completely determined by the cw laser and the electronic signals applied to the modulators. Alternatively, one can use mode-locked lasers to generate a frequency comb with a phase co­herent relationship between each wavelength component. The drawback with a conventional mode-locked laser is that the frequency comb can drift owing to both environmental effects and background quantum effects, such as fluctua­tions in the background spontaneous emission in the gain medium of the laser [3].

Recently, Hansche and co-workers developed a technique that produces a stabilized optical frequency comb based on a technique that requires a mode-locked laser to possess an octave of optical spectra [4]. A salient feature of this approach is that the frequencies of optical comb can be generated on an absolute frequency grid, i.e., the optical frequencies are precisely known to exist at exact multiples of the pulse repetition rate of the laser. A drawback, however is that the laser must possess an octave of optical bandwidth, and generally, the pulse repetition frequency is suf­ficiently low that it is difficult to have access to the individual comb components, owing to their relative close spacing. This feature of the close optical frequency spacing then makes the optical source difficult to employ in commercial applica­tions, such as wavelength division multiplexed optical communication networks.

Our work has focused on developing an optical source that produces a set of widely spaced optical frequencies compared to the octave spanning ap­proach so it becomes suitable for a broad range of communication and signal pro­cessing applications without the need of an octave of bandwidth, and with higher spectral purity and stability of the cw modulated approach. The approach is also self-referencing in that the optical frequency comb is reference to a secondary optical standard, such as a high-Q etalon. To achieve the wide optical channel spacing and high spectral purity, we engineer the optical cavity so that the gen­erated optical frequency comb has wide channel spacing and simultaneously a very narrow linewidth for each “tooth” of the frequency comb. These charac­teristics allow the source to possess very low noise, and possess excellent spec­tral purity for each comb component. In addition, our approach can be performed using any gain medium, e.g., semiconductor, so that the produced comb can be placed anywhere within the optical spectrum, e.g., uv, visible, near infrared, etc.

To achieve a stabilized comb of coherent, phase-locked optical fre­quencies, we engineer the optical cavity to possess wide mode spacing and nar­row linewidth. This is achieved by employing a nested cavity configuration that combines two cavities, where the main cavity has a finesse of 100 and a free spectral range of ~ 5.6 MHz, and a secondary internal cavity with a finesse of 1000 and a free spectral range of 10.287 GHz. The combined cavities gener­ate a frequency comb with a spacing determined by the internal cavity, and in­dividual narrow comb linewidths defined by the main cavity. The free spectral range of the secondary cavity also defines the laser’s pulse repetition frequency. The laser system schematic is shown in Fig. 1. The system may be regarded in two parts; the actively mod-locked laser cavity, and the Pound-Drever-Hall op­tical stabilization loop. A dispersion compensating fiber section of 3.5 meters is included to reduce the cavity dispersion. Active mode-locking is achieved via loss modulation using a Mach-Zehnder style modulator at 10.287 GHz. The driving signal to the modulator is obtained from an ultra low noise oscillator.

The purpose of the internal cavity Fabry Perot etalon (FPE) is two­fold. First, the inclusion of the etalon allows only a single phase locked mode group, or supermode, to lase. Without the inclusion of the etalon, ~1830 inter­leaved supermodes will compete, and the resulting random fluctuations in ampli­tude and phase will disturb the output pulse train. This noise manifests itself in the timing and amplitude noise spectra as a series of noise spurs, called super­mode noise, at multiples of the cavity fundamental frequency (5.6 MHz in this case). Also, the simultaneous lasing of different optical supermodes precludes the use of a single phase locked frequency comb with multigigahertz spacing. In the frequency domain, the FPE may be considered as a periodic bandpass filter that selects a single optical supermode. Without stabilization of the laser cav­ity, however, environmental influences will cause the optical frequencies to drift relative to the transmission peaks of the FPE. These frequency fluctuations will destabilize the mode-locking. The modes of the laser cavity are therefore stabi­lized to the FPE with the Pound-Drever-Hall (PDH) laser frequency stabilization method. The PDH stabilization loop uses the FPE to detect small changes to the optical frequencies of the laser to create an error signal that, after conditioning by a proportional gain-integration-differentiation (PID) controller, is fed back into a piezoelectric actuator to compensate for the frequency change. Thus supermode suppression and optical frequency stabilization are achieved simultaneously with a single intracavity FPE. The resulting performance of this laser produces a spectrally flat stabilized optical frequency comb of ~ 200 comb components on a 10.24 GHz grid. The individual comb linewidth is <500Hz with a stability of ~150 kHz, and has >50dB contrast. The generated periodic pulse train has an over­all timing jitter (1 Hz to 100 MHz) of ~ 3 femtoseconds, with an intensity noise of 0.023%. To our knowledge, this is the lowest jitter multi-gigahertz stabilized optical comb source. Owing to its well defined stable optical comb and low phase noise this laser has applications in photonic analog to digital conversion, coher­ent communication, arbitrary waveform generation and optical clock distribution.

To realize the potential processing speeds and accuracy that photonics promises, the use of stabilized phase coherent optical fre­quency combs is a step toward that vision. Our work shows that the gen­eration of stabilized optical frequency combs can be obtained with excel­lent stability without the need of octave spanning spectra with the cost effectiveness, electrical efficiency, and compactness of semiconductor diode lasers.

References

1. P. J. Delfyett, S. Gee, M. Choi, H. Izadpanah, W. Lee, S. Ozharar, F. Quinlan, T. Yilmaz, “Optical Frequency Combs from Semiconductor Lasers and Ap­plications in Ultra-wideband Signal Processing and Communications, IEEE Journal of Lightwave Technology, Vol. 24, No. 7, pp. 2701-2719, (2006).

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