NEWS AWARDS

ABOUTTHE 2009 IN PHYSICS

THE 2009 NOBELPRIZE IN PHYSICS I NOBEL COMMITTEE REWARDS RESEARCH IN TECHNOLOGY

/e Nobel Prizes in Physics of 2009 University of California at Berkeley, ged entirely his work. "/is has been have been awarded for two scientific and who joined aWer recei- the most important development in developments that have a profound ving his PhD and started work on the astronomy the last 30 years or so, if impact on both consumer techno- CCD. "My reaction was of absolute not more, for the simple reason that logy and scientific research. Charles delight, I found out that the work we the predecessor of all the electronic K. Kao of the Chinese University in did was actually worth the Nobel detectors was the photographic plate, Hong Kong was awarded the Nobel Prize," says Séquin. and the quantum efficiency of the Prize "for groundbreaking achieve- "I think it is great to give a prize for electronic plate was between 1 and 3 ments concerning the transmission something that is technology, cer- percent. Now, with the solid-state of light in fibres for optical commu- tainly for the science that it enabled," detector, the quantum efficiency nication. /e second half of the prize says Steve Howell, an astronomer at reaches almost 100 percent," says ᭢ Charles was awarded to two researchers from the Planetary Science Institute in Baade. Unlike photographic plates, Kao in his Bell Labs, Willard S. Boyle and Tucson,Arizona. CCDs allow the repeated exposure of laboratory at the Standard George E. Smith "for the invention of For astronomers, the invention of the the same area of the sky, making Telecommu- an imaging semiconductor circuit, CCD was indeed a revolution. For extremely faint objects visible. "/e nications the CCD sensor." Although the Dietrich Baade,the leader of the Opti- ultra-deep field images obtained with Laboratory in the U.K. in importance of the rewarded work is cal Detector Team of the European the Hubble Space Telescope are the the 1960s. evident,it came to many as a surprise. Organisation for Astronomical result of sixty hours of observations– (European Pressphoto It was a surprise to Carlo Séquin,now Research in the SouthernAtmosphere a tremendous number." says Baade. Agency) at the College of Engineering at the (ESO),in Garching,Germany,it chan- Howell still remembers how the ini- tial design of the Hubble Space Telescope incorporated photographic plates that would be parachuted to Earth or picked up by visiting crews. "/e study of distant supernovae, dark energy and dark matter, none of this would have been enabled without CCDs," says Howell. /e commercial impact of optical fibres is even more important than that of CCDs, but the impact on scientific research is definitely as great./e fast transmission of data in fibres not only allows the setting up of super-fast networks like "the grid" developed by CERN for the distribu- tion of data obtained with the LHC, but also of "virtual observatories" in astronomy and other areas of science.

08 EPN 40/6 AWARDS NEWS

Direct applications of optical fibres were working on a so-called "bubble the idea. "In this case they didn't do also abound, in photonics, memory" for computers, and not on that." he says.And he also comments research, and even in telescopes. an imaging device."If you are interes- on the fact that the 1966 paper by Baade explains how the spectrograph ted in the basic concept of the charge Kao [1], cited by the Nobel Commit- used in the search of exoplanets with transport, then I think it is absolutely tee, in which he outlines how optical HARPS (High Accuracy Radial Velo- reasonable to pick Boyle and Smith fibres can transport signals over long city Planet Searcher) is connected via because they had this crucial discus- distances, also has a co-author, optical fibres to ESO's 3.6-metre teles- sion in their office that lead to this George Hockham, who doesn’t share cope at the La Silla Paranal idea," says Séquin. "But if you read the Nobel Prize. Observatory in Chile. /e individual the report of the Nobel Committee,it It is clear that the researchers who feel fibres collect the light of a large num- is 90 percent about image sensors leW out are the victims of the rule of ber of stars,and carry the light to a and how to make image sensors of limiting the Nobel Prize to maximally spectrograph mounted in a vacuum high resolution," says Séquin. It was three recipients. Increasingly, vessel,making the extremely sensitive a colleague of Séquin at Bell labs, advances in technology and science instrument independent of telescope Michael Tompsett, who in fact built are the result of large teams.“Clearly motions and temperature changes. the first CCD, and who applied for a the development of a honest-to-God Unfortunately, the nomination of patent for the device. It was also viable CCD camera involved in the Boyle and Smith for the development Tompsett who devised the techno- order of 200 individuals,”comments of the CCD became the subject of a logy for reading out the information Séquin. Perhaps the Nobel Commit- controversy. During the days follo- stored on the CCD. "/is principle tee should relax its limitation on the wing the announcement of the Nobel was clearly invented by Tompsett," number of nominees. I laureates early October, several says Séquin. researchers questioned on a blog of According to Govind Agrawal, who III A. Hellemans IEEE Spectrum whether the duo leads the Nonlinear Fiber Optics really could be viewed as the inven- Group at the University of Rochester References tors of the CCD. "/e comments in Rochester, New York, the Nobel were flying back and forth,there is no Committee generally divided the [1] K.C. Kao and G.A. Hockham, Dielectric- Fibre Surface Waveguides for doubt that there is a controversy," prize between the team who got the optical frequencies, Proc. IEEE 113, says Séquin. In fact Boyle and Smith idea and the team who implemented 1151 (1966).

THE 2009 NOBELPRIZE IN PHYSICS II CHARLES KAO, PIONEER IN OPTICAL FIBRES

/e world is pending on a tiny and the coaxial cable CATV lines and Cables (STC) in Harlow,UK,and thread, a thread of glass. Optical connecting the users’ homes. Electri- there he developed his groundbrea- fibre is vastly deployed all over the cal signals get attenuated on the lossy king ideas of how to carry light with world,to carry our telephone conver- copper lines, necessitating lots of extremely low losses through glass sations, computer data, TV signals, amplifiers all over in the networks. fibre. He first presented his results in the internet with its exploding /e bandwidth of these lines is quite January 1966 in London to the Insti- gamma of services, etc. Our econo- limited, and is running out of steam tute of Electrical Engineers (IEE). mic, social and cultural activities in view of the fast growing capacity would come to a standstill without needs of the internet. Moreover, as Low-loss light guiding the huge communication streams the world’s resources are expiring, /e guiding of light in curved media which the tiny silica glass fibre is able copper gets ever more expensive. was already observed much earlier, to carry.When Samuel Morse intro- Charles Kao, who was born in 1933 e.g. by noticing that in illuminated duced the telegraph and Alexander in Shanghai, and got his PhD degree fountains light was guided by the Graham Bell the telephone,the world in Electrical Engineering in the curved water beams. /e light gui- was dependent on copper wires.And Imperial College London in 1965, ding is actually realized by‘total still large parts of the communication recognized these shortcomings internal reflection’: light propagating networks are using copper, in parti- already in the mid 60’s. He worked as in a material with a high refractive cular the twisted-pair telephone lines an engineer in Standard Telephones index is reflected at the interface with III

EPN 40/6 09 NEWS AWARDS

III a medium with lower refractive index, provided that the incidence angle on this interface is larger than the critical angle. As this reflection is very efficient and causes negligible losses, light can be confined and gui- ded through the water beam. Obviously more stable solutions than water beams are needed, so similar experiments were done with homo- geneous threads of glass. Endoscopy could be done with many of these glass threads united in a single cable. However, small scratches and other ᭡ FIG. 1: Silica optical fibres (diameter 125μm each) irregularities at the surface of the glass destruct the total internal reflec- Glass in the US indeed demonstrated Hence this modal dispersion pheno- tion process, and light leaks out. light guiding in such optical fibre menon limits the rate at which Hence the losses of such homoge- with less than 20 dB/km loss. pulses can be transmitted, so the neous threads were too high for Modern optical fibre has a standar- bandwidth of the fibre. /e modal guiding light over larger distances. dized outer diameter of only 125 dispersion can be reduced by accele- Moreover, impurities in the glass micrometer, within 1 μm. /is is rating the light rays which are itself contributed to the losses. about the thickness of a human hair making the larger excursions when Charles Kao came up with fused (see Fig. 1). Regarding attenuation, it travelling through the core, so by silica (silicon dioxide) as the perfect has made a huge progress since its reducing the refractive index of the material for very low loss light gui- invention, while still following Kao’s core towards the cladding, see Fig. 2. ding. And the fibre structure itself principles. It now conveys more than Such ‘graded-index multimode fibre’ should not be a homogeneous 95% of the light through 1 kilometer shows a clearly larger bandwidth thread, but should have an inner of fibre, i.e. it has a loss of less than than its step-index counterpart. core having a high refractive index, 0.2 dB/km. /is has only been possi- Obviously,a single-mode fibre shows ᭢ Professor surrounded by a glass cladding with ble by bringing the purity of the silica hardly any pulse broadening, and Charles Kao (third from a lower index. /us the boundary glass to the extreme, using precisely thus has the ultimate bandwidth. right) poses was nicely protected and could serve controlled environmental conditions, Single-mode fibre is by far the most shoulder-to- as a reliable close-to-perfect mirro- very sophisticated chemical vapour wide-spread fibre type. Multimode shoulder with stu- ring surface for guiding the light deposition techniques for building a fibre is only applied for shorter links, dents from beam. Kao’s claim which he presen- structured perform, excluding every such as in in-building networks. the Chinese ted in 1966 was that, with fused silica tiny amount of water, and drawing /anks to its larger core,it is easier to University in Hong Kong glass and the core-cladding structure, the preform into a very tightly connect than single-mode fibre. on the first losses of less than 20 decibels per controlled fibre. day of the kilometer should be feasible,i.e. more /e diameter of the fibre’s core has a Dispersion and losses 1994-95 aca- demic year. than 1% of the light power should major impact on the light guiding /e bandwidth of single-mode fibre is Copyright © still remain aWer propagation properties: when it is on the order of mainly limited by material dispersion The Chinese University of through 1 kilometer of fibre. In 1970, the wavelength, it can be shown that (since the refractive index of the silica Hong Kong Keck and co-workers at Corning the fibre is able to guide light only in glass is slightly dependent on the a single mode: hence it is called a wavelength) and by waveguide disper- single-mode optical fibre (see Fig. sion (since the electrical field spreads 2).When it is much thicker, many out from the core into the cladding, more modes can be guided: a multi- and this spreading becomes larger at mode fibre. Each mode has a increasing wavelength). Material dis- different propagation time; thus an persion and waveguide dispersion optical pulse, which is guided by have opposite signs, and can cancel these modes, will get dispersed and each other. For silica glass, this hap- is broadened when it arrives at the pens at a wavelength of about 1.31 fibre’s end.When pulses broaden, μm, the so-called ‘zero-dispersion they cannot be put closely together wavelength’.At this wavelength, the anymore without serious overlap. fibre reaches its ultimate bandwidth,

10 EPN 40/6 AWARDS NEWS

and the bandwidth of the whole fibre doped optical fibre can amplify optical link is then only limited by the spec- signals directly without converting tral purity of the laser transmitter. them first into electrical signals.Many /e fibre’slosses depend on the wave- wavelength channels can be amplified length of the light, and reach their all-optically and simultaneously, lowest value around 1.55 μm,which is which makes such an optical amplifier in the near infra-red. As Fig. 3 shows, an essential component in long-haul the low-loss wavelength region of the wavelength-multiplexed systems. fibre represents a huge optical fre- quency range, and thus an extremely Fibre-to-the-home and large capacity for guiding telecommu- fibre-in-the-home nication signals. A , which Whereas silica fibre has conquered is another crucial element in an opti- telecommunication networks in the cal fibre communication link, can long-haul parts, spanning oceans, send light pulses at a very high repeti- continents, but also countries and tion rate, at tens of giga-Hertz, but cities, the final drop to the user’s only occupies a tiny part of this optical home is in most places still on twis- frequency range. But many of these ted-pair copper lines and/or coaxial laser diodes, each operating at a copper cables. /is final access drop slightly different optical frequency,can is more and more becoming the bot- be put in parallel and thus together tleneck in offering high capacity to convey massive amounts of data. the user. Hence fibre is now increa- Using this so-called ‘wavelength divi- singly being installed all the way to sion multiplexing’,in the laboratory the homes in access networks, repla- transmission has been achieved with cing the copper lines,and by virtue of speeds exceeding 21 terabits per its tremendous capacity hosting all second. Such a capacity would allow the services offered by the copper that one half of the world’s popula- media (triple play: video, voice, and tion can have a phone conversation data) and any service yet to come! In made much thicker, and is ductile. ᭡ FIG. 2: Light with the other half, just through one Japan, fibre-to-the-home has already /is makes it much easier to handle guiding by optical fibres tiny silica optical fibre as thick as a outnumbered the copper twisted pair and to install, even by unskilled per- ©istockphoto human hair! connections (the digital subscriber sons. Its losses are by far not as low as Nowadays optical fibre is installed all line, DSL).And the US and many those of silica fibre, but as in-home over the world. /e total length European countries are progressing link lengths are short, that is not a amounts to some 1 billion kilometers, in the same direction. Connection show-stopper. Like the silica fibre 25000 times the circumference of the speeds to the home are typically 100 proposed by Kao, also the POF has a earth! Many fibre links are connecting Mbit/s both to and from the home; in core-cladding structure. Its large dia- the continents together; e.g.,the trans- Japan, even 1 Gbit/s is introduced. meter causes a high modal atlantic links bridge the ocean But Fibre to the Home is not the end dispersion, and thus severely limits between Europe and North America, game yet in the quest of bringing the its bandwidth for longer lengths. But ca.6000 km,and the transpacific links ultimate communication highway to again, lengths are short, and thus this ᭢ FIG. 3: Attenuation of between the west coast of the US and the user.AWer having reached the is not lethal. Special techniques are silica single- Japan, ca. 9000 km, with an interme- doorstep, the highway needs to be being developed to convey Gbit/s mode fibre . diate landing point in Hawaii. extended into the home, up to the Although the fibre has very low losses, devices of the user himself. /us such distances cannot be bridged research is now being directed to without amplification. /e advent of optical fibre systems for in-home, the optical fibre amplifier,in particular where it becomes crucially important the erbium-doped fibre amplifier to make the system robust, and easy (EDFA) was another landmark in the to install, preferably in a do-it- evolution history of optical communi- yourself fashion. Silica fibre is brittle cation systems.When doped with the and has to be installed with preci- rare earth material erbium which is sion tools and by skilled personnel. brought into an excited state by opti- As an alternative, plastic optical fibre cal pumping with another laser, the (POF) is coming up,which can be

EPN 40/6 11 NEWS AWARDS

III data streams over POF networks. III Ton Koonen, Telecommunication Industry, as Also techniques are being investiga- COBRA Institute, Eindhoven Uni- technical manager with Bell Labora- ted to carry microwave radio signals versity of Technology,Eindhoven, tories in AT&T Network Systems and over the fibre in order to meet the /e Netherlands in Lucent Technologies. His current user’s needs for broadband wireless research interests include broadband communication without having to About the author communication technologies and put comprehensive microwave radio Ton (A.M.J.) Koonen is a Full Pro- networks, in particular fiber access equipment everywhere. fessor at Eindhoven University of and in-building networks, radio- So by pioneering optical fibre, Technology, in the Electro-optical over-fiber networks, and optical Charles Kao has opened the road Communication Systems Group, packet-switched networks.Prof.Koo- towards real broadband communi- being Chairman of this group since nen is a Bell Laboratories Fellow cation, where the sky is the limit,and 2004. He worked for over 20 years in since 1998, an IEEE Fellow since light is shining into a bright future applied research in broadband tele- 2007, and an elected member of the where we can communicate with communication systems: as a IEEE LEOS Board of Governors each other without any borders! I member of technical staff at Philips since 2007.

THE 2009 NOBELPRIZE IN PHYSICS III W.BOYLE AND G.SMITH FORTHE CCD

October 6th, 2009 was a great day for tured by means of CCD cameras; Kodak, Philips, E2V, Fairchild, the solid-state imaging community. many medical diagnoses are relying DALSA, LG, /omson, Sarnoff, /e went to on CCD images as well. Other SITe, Ford Aerospace. Willard Boyle and George Smith,two application fields are security,astro- • on the imaging technology: aWer the Bell Labs co-workers who invented nomy and scientific cameras. In introduction of the CCDs, the classi- the Charge-Coupled Device (CCD). many applications these days CCDs cal imaging tube quickly disappeared /e CCD has created a revolution in are being challenged by CMOS from the scene.CCDs are more com- Science and technology as well as in (Complementary Metal Oxide pact, lighter in weight, less power ᭢ The two society at large. Semiconductors) image sensors,but hungry, lower supply voltage, no inventors of I am wondering whether W.Boyle and it can easily be understood that burn-in effects, no image lag, no the CCD with one of the G.Smith ever realized that their inven- CCDs paved the way in solid-state maintenance and immune to electro- very first tion would have such a great impact: imaging, for CMOS as well; magnetic fields. CCDs only had CCD cam- eras, • on society : these days everyone has • on the semiconductor business: advantages over the imaging tubes, developed a digital still camera, many have a many companies made quite a pro- even a lower price. /e CCDs ope- by Bell Labs, camcorder all provided with a CCD, fitable consumer business out of ned a great new field of imaging illustrating their great some even with three CCDs.All TV CCDs. Examples are Sony, Panaso- applications that were never possible invention. images we see today are being cap- nic, Sharp, Toshiba, NEC, FujiFilm, without solid-state image sensors, • on the scientific and technical com- munity: the basic CCD invention of Boyle and Smith was a great ins- piration for many other great engineers: Walden invented the buried channel CCD, Esser inven- ted the peristaltic CCD, Kosonocky the floating diffusion and White added the correlated-double sam- pling. But the CCD performance improved quite a lot aWer the intro- duction of the pinned photodiode by Teranishi. From that moment, the CCD business really started to boom. Many other important inventions were inspired by the work of W.Boyle and G. Smith.

12 EPN 40/6 AWARDS NEWS

Fabricationandperformance see examples in Figs. 2 and 3). /eir /e design, lay-out and fabrication of image quality is better and the cost these capacitors needs to be done in advantage of CMOS technology is such a way that it allows a smooth much less or even non-existing. transfer of the charge packets./is Although the CCD is celebrating its transport is not perfect. If its efficiency 40th anniversary, it still deserves its is not 100 %, some electrons from the place in the digital imaging business. I charge packets will get lost. In the very earlydaysof theCCDs,thetransfereffi- III Albert euwissen, ciency was about 99 %, but in modern DelW University of Technology (the CCDs the transfer efficiency can be as Netherlands) and Harvest Imaging high as 99.99999 %. (Bree, Belgium) ᭡ FIG. 1: Shown here is a 48 Mpixel CCD Ononehand,theindustrytriestomake imager with a size of 48 mm x 36 mm, used in highest-end thepixelsassmallaspossible,butonthe About the author (courtesy DALSA, Eindhoven). otherhand,thenumberof pixelsputon Prof. Albert J.P.-euwissen (1954) asingleCCD chip isincreasing.Consu- received his PhD in electrical enginee- Principle of CCD mer devices have pixel counts up to 14 ring from the Catholic University of A Charge-Coupled Device essen- Mpixels, but imagers for professional Leuven (Belgium).As of 2001 he is tially consists of a 2-D array of tiny use (e.g. astronomy,video-grammetry) part-time professor at DelW University pixels which convert light into electri- have pixel counts ranging to over 150 of Technology (DelW, Netherlands) cal charge (see Fig. 1). Each pixel may Mpixels. Taking into account the 4 where he teaches courses in solid-state be considered as a small group of capacitors per pixel, this gives rise to imaging and coaches PhD students in capacitors carrying a charge./e wor- over 600,000,000 individual capacitors their research on CMOS image sensors. king principle of a CCD is based on on a single chip! He is presently running his own com- the transfer of charge packets from With respect to the performance of the pany “Harvest Imaging”,focusing on one capacitor to the next one./e CCDs,inmanyaspectstheyperformas training,teaching and coaching of peo- charge is thus transported across the well as the human eye (e.g. sensitivity, ple active in the field of digital imaging. array, and read out at one corner. low-light level imaging,speed).In some Pixels located close to the output aspects the CCDs do even better than amplifier have to undergo just a few the human eye (noise performance, transport cycles, while the charge of radiation hardness), but in others, the pixels located at the far side of the CCDs still can learn from the human output stage has to move over quite a eye (power dissipation, parallel proces- long distance towards the output. sing of the information). /e image captured by the CCD can be easily reconstructed based on the Future perspectives fact that the pixels become available at CCDs do need a dedicated produc- the CCD output in a serial way,and in tion process to fabricate the image a similar sequence they are displayed sensors, and unfortunately, these pro- on a monitor. cesses are not available on every ᭡ FIG. 2: HDTV camera containing 3 CCD imagers. The pixels of the imagers are designed in such a way that the camera /e transport takes place in the sili- corner of the street. /is observation can be used according to different HDTV standards (courtesy con material, and is driven by digital makes the CCD rather expensive Grass Valley, Breda). pulses. In its simplest form, every compared to its competing techno- ᭢ FIG. 3: CCD cameras intended for industrial vision applica- CCD pixel is composed out of 4 of logy, being the CMOS . tions.The imagers have pixel counts in the range of 1 Mpixels - 8 Mpixels and can produce monochrome and colour images at such capacitors.With 4 capacitors per Especially for consumer devices (e.g. higher frame rates (courtesy of Adimec, Eindhoven). pixel, the charge packets can be shif- mobile phones), the outstanding ima- ted from one pixel to the next one ging performance of the CCD cannot without being mixed up. Every capa- compensate for the cost difference citor can be extremely small, for a between CCDs and CMOS image classical consumer imager, the pixels sensors. But on the other hand, for go down to 2.0 μm or even less. /at very specific market segments as well means that the individual CCD capa- as for professional applications, the citor is less than 0.5 μm.Note that CCDs are superior over CMOS image this is just about the wavelength of sensors (e.g., broadcast applications, visible light. astronomy, medical instrumentation;

EPN 40/6 13