MICROELECTRONIC INTERCONNECTIONS AND MICROASSEMBL Y WORKSHOP 18-21 May 1996, Prague, Czech Republic Conference Organizers: George Harman, NIST (USA) and Pavel Mach (Czech Republic) Summary of the Technical Program Thirty two presentations were given in eight technical sessions at the Workshop. A list of these sessions and their chairpersons is attached below. The Workshop was devoted to the technical aspects of advanced interconnections and microassembly, but also included papers on the education issues required to prepare students to work in these areas. In addition to new technical developments, several papers presented overviews predicting the future directions of these technologies. The basic issue is that electronic systems will continue to be miniaturized and at the same time performance must continue to improve. Various industry roadmaps were discussed as well as new smaller packaging and interconnection concepts. The newest chip packages are often based on the selection of an appropriate interconnection method. An example is the chip-scale package, which has horizontal (x-y) dimensions,;; 20% larger than the actual silicon chip itself. The chip is often flip-chip connected to a micro ball-grid-array, but direct chip attach was described also. Several papers described advances in the manufacture of such packages.

Micro Electro Mechanical Systems (MEMS) is already about a billion dollars a year industry and is growing rapidly. So far major emphasis has been placed on the fabrication processes for various devices. There are serious issues related to tribology, mechanics, surfacechemistry and materials science in the operationand manufacturingof many MEMS devices and these issues are preventing an even faster commercialization. Very little is understood about tribology and mechanical properties on micro- to nanoscales of the materials used in the construction of MEMS devices. The MEMS community needs to be exposed to the state-of-the-artoftribology and vice versa. Fundamental understanding of friction/stiction, wear and the role of surface contamination and environmental debris in micro devices is required. There are significantadhesion, friction and wear issues in manufacturing and actual use, facing the MEMS industry. Very little is understood about the tribology of bulk silicon and polysilicon films used in the construction ofthese microdevices. These issues are based on surface phenomenaand cannotbe scaled down linearly and these become increasingly important with the small size of the devices. Continuum theory breaks down in the analyses, e. g. in fluid flow of micro-scale devices. Mechanical properties ofpolysilicon and other films are not well characterized. Roughness optimization can help in tribological improvements. Monolayers of lubricants and other materials need to be developed for ultra-low friction and near zero wear. Hard coatings and ion implantation techniques hold promise.

Polymer science is a technology-driven science. More often than not, technological breakthroughs opened the gates to rapid fundamental and theoretical advances, dramatically broadening the understanding of experimental observations, and expanding the science itself. Some of the breakthroughs involved the creation of new materials. Among these one may enumerate the vulcanization of natural rubber, the derivatization of cellulose, the giant advances right before and during World War II in the preparation and characterization of synthetic elastomers and semi crystalline polymers such as polyesters and polyamides, the subsequent creation of aromatic high-temperature resistant amorphous and semi-crystal line polymers, and the more recent development of liquid-crystalline polymers mostly with n~in-chain mesogenicity. other breakthroughs involve the development of powerful characterization techniques. Among the recent ones, the photon correlation spectroscopy owes its success to the advent of laser technology, small angle neutron scattering evolved from n~clear reactors technology, and modern solid-state nuclear magnetic resonance spectroscopy exists because of advances in superconductivity. The growing need for high modulus, high-temperature resistant polymers is opening at present a new technology, that of more or less rigid networks. The use of such networks is rapidly growing in applications where they are used as such or where they serve as matrices for fibers or other load bearing elements. The rigid networks are largely aromatic. Many of them are prepared from multifunctional wholly or almost-wholly aromatic kernels, while others contain large amount of stiff difunctional residus leading to the presence of many main-chain "liquid-crystalline" segments in the "infinite" network.

A variety of ceramic materials has been recently shown to exhibit nonlinear stress strain behavior. These materials include transformation-toughened zirconia which undergoes a stress-induced crystallographic transformation in the vicinity of a propagating crack, microcracking ceramics, and ceramic-fiber reinforced ceramic matrices. Since many of these materials are under consideration for structural applications, understanding fracture in these quasi-brittle materials is essential. Portland cement concrete is a relatively brittle material. As a result mechanical behavior of concrete, conventionally reinforced concrete, prestressed concrete and fiber reinforced concrete is critically influenced by crack propagation. Crack propagation in concrete is characterized by a fracture process zone, microcracking, and aggregate bridging. Such phenomena give concrete toughening mechanisms, and as a result, the macroscopic response of concrete can be characterized as that of a quasi-brittle material. To design super high performance cement composites, it is essential to understand the complex fracture processes in concrete. A wide range of concern in design involves fracture in rock masses and rock structures. For example, prediction of the extension or initiation of fracture is important in: 1) the design of caverns (such as underground nuclear waste isolation) subjected to earthquake shaking or explosions, 2) the production of geothermal and petroleum energy, and 3) predicting and monitoring earthquakes. Depending upon the grain size and mineralogical composition, rock may also exhibit characteristics of quasi-brittle materials."

It is not good to have zeal without knowledge * . . . Book of Proverbs This volume constitutes the proceedings of the Third International Workshop on Materials Processing at High Gravity. It offers the latest results in a new field with immense potential for commercialization, making this book a vital resource for research and development professionals in industry, academia and government. We have titled the proceedings Centrifugal Materials Processing to emphasize that centrifugation causes more than an increase in acceleration. It also introduces the Coriolis force and a gradient of acceleration, both of which have been discovered to play important roles in materials processing. The workshop was held June 2-8, 1996 on the campus of Clarkson University in Potsdam, New York, under the sponsorship of Corning Corporation and the International Center for Gravity Materials Science and Applications. The meeting was very productive and exciting, with energetic discussions of the latest discoveries in centrifugal materials processing, continuing the atmosphere of the first workshop held in 1991 at Dubna (Russia) and the second workshop held in 1993 in Potsdam, New York. Results and research plans were presented for a wide variety of centrifugal materials processing, including directional solidification of semiconductors, crystallization of high Tc superconductors, growth of diamond thin films, welding, alloy casting, solution behavior and growth, protein crystal growth, polymerization, and flow behavior. Also described were several centrifuge facilities that have been constructed for research, with costs beginning at below $1000.

Materials Chemistry is rapidly emerging as a key component of contemporary science. The strongly interdisciplinary nature of the field requires input from all branches of chemistry, from crystallography, from solid state physics and from computational and theoretical techniques. This book aims to give a coherent survey of the field by considering all the major aspects of the current study of the chemistry of materials. Early chapters emphasise basic principles and techniques. Strong emphasis is given to new techniques and technologies, for example, the opportunities opened up by new synchrotron sources in crystallography, and new computational techniques in simulation studies of complex materials. Characterisation techniques including crystallographic, microscopic and spectroscopic techniques are then described. Key contemporary themes such as atomic transport, reactivity and catalysis are reviewed. Later chapters focus on specific dasses of material, induding solid state ionics, ceramics (induding giant magneto-resistance and high temperature superconducting solids), microporous and molecular materials. We hope that the book provides a snapshot of the scientific and technological challenges in this fast developing field. The editors would like to thank the NATO Scientific Affairs Division for funding the School on which this volume is basedj financial contribution from Johnson Matthey Technology Centre is also gratefully acknowledged. We are most grateful to Mrs Jean Conisbee for all her efforts in preparing the manuscript.

This book represents the proceedings of the First International Conference on Frontiers of Polymer Research held in New Delhi, India during January 20-25, 1991. Polymers have usually been perceived as substances to be used in insulations, coatings, fabrics, and structural materials. Defying this classical view, polymers are emerging as a new class of materials with potential applications in many new technologies. They also offer challenging opportunities for fundamental research. Recognizing a tremendous growth in world wide interest in polymer research and technology, a truly global "1st International Conference on Frontiers of Polymer Research" was organized by P. N. Prasad (SUNY at Buffalo), F. E. Karasz (University of Massachusetts) and J. K. Nigam (Shriram Institute for Industrial Research, India). The 225 participants represented 25 countries and a wide variety of academic, industrial and government groups. The conference was inaugurated by the Prime Minister of India, Mr. Chandra Shekhar and had a high level media coverage. The focus of the conference was on three frontier areas of polymer research: (i) Polymers for photonics, where nonlinear optical properties of polymers show great promise, (ii) Polymers for electronics, where new conduction mechanisms and photophysics have generated considerable enthusiasm and (iii) High performance polymers as new advanced polymers have exhibited exceptionally high mechanical strength coupled with light weight.

The Workshop on Physics and Application of Non-crystalline Semiconductors in Optoelectronics was held from 15 to 17 October 1996 in Chisinau. republic of Moldova and was devoted to the problems of non-crystalline semiconducting materials. The reports covered two mjlin topics: theoretical basis of physics of non -crystalline materials and experimental results. In the framework of these major topics there were treated many subjects. concerning the physics of non-crystalline semiconductors and their specific application: -optical properties of non-crystalline semiconductors; -doping of glassy semiconductors and photoinduced effects in chalcogenide glasses and their application for practical purposes; -methods for investigation of the structure in non-crystalline semiconductors -new glassy materials for IR trasmittance and optoelectronics. Reports and communications were presented on various aspects of the theory. new physical principles. studies of the atomic structure. search and development of optoelectronics devices. Special attention was paid to the actual subject of photoinduced transformations and its applications. Experimental investigations covered a rather wide spectrum of materials and physical phenomena. As a novel item it is worth to mention the study of nonlinear optical effects in amorphous semiconducting films. The third order optical non linearities. fast photoinduced optical absorption and refraction. acusto-optic effects recently discovered in non-crystalline semiconductors could potentially be utilised for optical signal processing. The important problems of photoinduced structural transformations and related phenomena. which are very attractive and actual both from the scientific and practical points of view. received much attention in discussions at the conference."

Microwave Physics and Techniques discusses the modelling and application of nonlinear microwave circuits and the problems of microwave electrodynamics and applications of magnetic and high Tc superconductor structures. Aspects of advanced methods for the structural investigation of materials and of MW remote sensing are also considered. The dual focus on both HTSC MW device physics and MW excitation in ferrites and magnetic films will foster the interaction of specialists in these different fields.

Conventional materials, such as nickel based alloys, will not be able to match the required performance specifications for the future generation of high temperature materials. This book reviews the characteristics and potential of a wide range of candidate superalloy replacements, such as ceramics, intermetallics, and their composites. Particular attention is devoted to the problems of processing and design with these materials.

The phenomenonofspontaneous ordering in semiconductoralloys, which can be categorized as a self-organized process, is observed to occur sponta neously during epitaxial growth of certain ternary alloy semiconductors and results in a modification of their structural, electronic, and optical properties. There has been a great dealofinterest in learning how to control this phenome non so that it may be used for tailoring desirable electronic and optical properties. There has been even greater interest in exploiting the phenomenon for its unique ability in providing an experimental environment of controlled alloy statistical fluctuations. As such, itimpacts areasofsemiconductorscience and technology related to the materials science ofepitaxial growth, statistical mechanics, and electronic structure of alloys and electronic and photonic devices. During the past two decades, significant progress has been made toward understanding the mechanisms that drive this phenomenon and the changes in physical properties that result from it. A variety of experimental techniques have been used to probe the phenomenon and several attempts made atproviding theoretical models both for the ordering mechanisms as well as electronic structure changes. The various chapters of this book provide a detailed account of these efforts during the past decade. The first chapter provides an elaborate account of the phenomenon, with an excellent perspective of the structural and elec tronic modifications itinduces.

This book is devoted to a nontraditional class of materials which are manufactured by the melt-blowing process. The text examines the structure and main properties of melt-blown materials as conditioned by peculiarities of overheated polymer melt spraying in oxidizing medium. Information is given about filtering mechanisms and the main types of polymer fibrous filtering materials.

The study of phase transformations in substitutional alloys, including order disorder phenomena and structural transformations, plays a crucial role in understanding the physical and mechanical properties of materials, and in designing alloys with desired technologically important characteristics. Indeed, most of the physical properties, including equilibrium properties, transport, magnetic, vibrational as well as mechanical properties of alloys are often controlled by and are highly sensitive to the existence of ordered compounds and to the occurrence of structural transformations. Correspondingly, the alloy designer facing the task of processing new high-performance materials with properties that meet specific industrial applications must answer the following question: What is the crystalline structure and the atomic configuration that an alloy may exhibit at given temperature and concentration? Usually the answer is sought in the phase-diagram of a relevant system that is often determined experimentally and does not provide insight to the underlying mechanisms driving phase stability. Because of the rather tedious and highly risky nature of developing new materials through conventional metallurgical techniques, a great deal of effort has been expended in devising methods for understanding the mechanisms contrOlling phase transformations at the microscopic level. These efforts have been bolstered through the development of fully ab initio, accurate theoretical models, coupled with the advent of new experimental methods and of powerful supercomputer capabilities.

The Microsystems Series has as its goal the creation of an outstanding set of textbooks, references, and monographs on subjects that span the broad field of microsystems. Exceptional PhD dissertations provide a good starting point for such a series, because, unlike monographs by more senior authors, which must compete with other professional duties for attention, the dissertation becomes the sole focus of the author until it is completed. Conversion to book form is then a streamlined process, with final editing and book production completed within a few months. Thus we are able to bring important and timely material into book form at a pace which tracks this rapidly developing field. Our first four books in the series were drawn from the more physics-oriented side of the microsystems field, including such diverse subjects as computer-aided design, atomic-force microscopy, and ultrasonic motion detection. Now, with Sangeeta Bhatia's work, we enter the realm of biology. Her use of artifically structured substrates to encourage the liver cells to form orderly assemblies is a fine example of how microfabrication technology can contribute to cell biology and medicine. I am pleased to be able to add this very new and very interesting work to the Microsystems Series. Stephen D. Senturia Cambridge MA Microfabrication in Tissue Engineering and Bioartificial Organs Foreword One of the emerging applications of microsystems technology in biology and medicine is in the field of tissue engineering and artificial organs. In order to function, cells need to receive proper signals from their environment.

Organic solids exhibit a wide range of electrical and related properties. They occur as crystals, glasses, polymers and thin films; they may be insulators, semiconductors, conductors or superconductors; and they may show luminescence, nonlinear optical response, and complex dynamical behaviour. The book provides a broad survey of this area, written by international experts, one third being drawn from Eastern Europe. Electrical, optical, spectroscopic and structural aspects are all treated in a way that gives an excellent introduction to current themes in this highly interdisciplinary and practically important area. The coverage is especially strong in the areas where electrical and optical properties overlap, such as photoconductivity, electroluminescence, electroabsorption, electro-optics and photorefraction.

Composite materials are increasingly used in many applications because they offer the engineer a range of advantages over traditional materials. They are often used in situations where a specified level of performance is required, but where the cost of testing the materials under the extremes of those specifications is very high. In order to solve this problem, engineers are turning to computer Modelling to evaluate the materials under the range of conditions they are likely to encounter. Many of these analyses are carried out in isolation, and yet the evaluation of a range of composites can be carried out using the same basic principles. In this new book the editor has brought together an international panel of authors, each of whom is working on the analysis and Modelling of composite materials. The overage of the book is deliberately wide; to illustrate that similar principles and methods can be used to model and evaluate a wide range of materials. It is also hoped that, by bringing together this range of topics, the insight gained in the study of one composite can be recognized and utilized in the study of others. Professional engineers involved in the specification and testing of composite material structures will find this book an invaluable resource in the course of their work. It will also be of interest to those industrial and academic engineers involved in the design, development, manufacture and applications of composite materials.

Despite the significant progress, which has been made in developing of ceramic materials desired for engineering applications, their mass production is still not on expected level. Among the key factors hindering higher exploitation of these materials the problems in processing were identified. The processing comprises powder production, mixing techniques, forming, and sintering. All of them are equally important and all of them can introduce defects into the material. Besides improvement in processing, the properties of ceramic materials can be considerably improved by the creation of composites. Composites formed at micro or macro level are able to form more flaw-tolerant material. Considerable research activities, working on above mentioned phenomena are in progress at industrial laboratories as well as other research centres. This volume presents the contributions to the Advanced Research Workshop "Engineering Ceramics '96" with 65 participants from 21 countries held on 12th - 15th May 1996 at Smolenice Castle, Slovakia, the conference site of Slovak Academy of Sciences. The book covers research activities on engineering ceramic materials and gives an overview with respect to recent developments.

Intensive research on zeolites, during the past thirty years, has resulted in a deep understanding of their chemistry and in a true zeolite science, including synthesis, structure, chemical and physical properties, and catalysis. These studies are the basis for the development and growth of several industrial processes applying zeolites for selective sorption, separation, and catalysis. In 1983, a NATO Advanced Study Institute was organized in Alcabideche (portugal) to establish the State-of-the-Art in Zeolite Science and Technology and to contribute to a better understanding of the structural properties of zeolites, the configurational constraints they may exert, and their effects in adsorption, diffusion, and catalysis. Since then, zeolite science has witnessed an almost exponential growth in published papers and patents, dealing with both fundamentals issues and original applications. The proposal of new procedures for zeolite synthesis, the development of novel and sophisticated physical techniques for zeolite characterization, the discovery of new zeolitic and related microporous materials, progresses in quantum chemistry and molecular modeling of zeolites, and the application of zeolites as catalysts for organic reactions have prompted increasing interest among the scientific community. An important and harmonious interaction between various domains of Physics, Chemistry, and Engineering resulted therefrom.

The Eighth Rochester Conference on Coherence and Quantum Optics was held on the campus of the University of Rochester during the period June 13-16,2001. This volume contains the proceedings of the meeting. The meeting was preceded by an affiliated conference, the International Conference on Quantum Information, with some overlapping sessions on June 13. The proceedings of the affiliated conference will be published separately by the Optical Society of America. A few papers that were presented in common plenary sessions of the two conferences will be published in both proceedings volumes. More than 268 scientists from 28 countries participated in the week long discussions and presentations. This Conference differed from the previous seven in the CQO series in several ways, the most important of which was the absence of Leonard Mandel. Professor Mandel died a few months before the conference. A special memorial symposium in his honor was held at the end of the conference. The presentations from that symposium are included in this proceedings volume. An innovation, that we believe made an important contribution to the conference, was the inclusion of a series of invited lectures chaired by CQO founder Emil Wolf, reviewing the history of the fields of coherence and quantum optics before about 1970. These were given by three prominent participants in the development of the field, C. Cohen-Tannoudji, 1. F. Clauser, and R. I. Glauber.

From 5 to 15 August 1984, a group of 79 physicists from 61 laboratories in 26 countries met in Erice for the 22nd Course of the International School of Subnuclear Physics. The countries represented were Austria, Belgium, Brazil, Bulgaria, Canada, People's Republic of China, Denmark, the Federal Republic of Germany, France, Greece, Hungary, Iran, Israel, Italy, Japan, Korea, Malaysia, Mexico, the Netherlands, Pakistan, Poland, Sweden, Switzerland, Turkey, the United Kingdom, the United States of America. The School was sponsored by the Italian Ministry of Public Education (MPI), the Italian Ministry of Scientific and Technologi cal Research (MRST), the Regional Sicilian Government (ERS), and the Weizmann Institute of Science. The programme of the School was devoted to a review of the most significant results in theoretical and experimental research work on the interactions between what we believe today are the point like constituents of the world: quarks and leptons. It should however not be forgotten that many problems are still to be understood: especially in the forefront of the correla tion between quarks and leptons. This game started in 1966 with the proposal for "leptonic quarks" and went on with "preons" and "rishons" just to quote the most famous attempts to unify these two worlds."

The authors of this contribution to the literature of resonance spectroscopy in paramagnetic systems are primarily concerned with the properties of the rare earth ions and, as such, the formal derivation of crystal field theory is set out in a manner which reflects this dominant interest. The ions of the 3d transition group are perhaps given too cursory a treatment in Chapter Two for those students of RF spectroscopy who have a somewhat less rare-earth oriented interest in the subject. Since the exam ples cited in the text do include some 3d transition ions, it is perhaps worthwhile in a preface of this sort to extend the broad theoretical concepts and group characteriza tion of Chapter Two to cover, in a somewhat more detailed manner, the derivation of the spin-Hamiltonian for this case. In Chapter Two, mention is made of the fact that for the 4f rare earth ions the spin orbit coupling energy is in general large compared to the crystal field influence of the surrounding ligand matrix. In such a case, the quantum number J is a good quantum number for the rare earth ion in question and the crystal field effects are taken into account within 1M, states. In this formulation, which is pursued in detail in this book, the effects of spin-orbit coupling have been taken care of at the very outset by the d "ining of the 1M, states."

This 6th International Symposium on Thermal Expansion, the first outside the USA, was held on August 29-31, 1977 at the Gull Harbour Resort on Hecla Island, Manitoba, Canada. Symposium Chairman was Ian D. Peggs, Atomic Energy of Canada Limited, and our continuing sponsor was CINDAS/Purdue University. We made considerable efforts to broaden the base this year to include more users of expansion data but with little success. We were successful, however, in establishing a session on liquids, an area which is receiving more attention as a logical extension to the high-speed thermophysical property measurements on materials at temperatures close to their melting points. The Symposium had good international representation but the overall attendance was, disappointingly, relatively low. Neverthe less, this enhanced the informal atmosphere throughout the meeting with a resultant frank exchange of information and ideas which all attendees appreciated. A totally new item this year was the presentation of a bursary to assist an outstanding research student to attend the Symposium. We were delighted to welcome Mr. Benedick Fraass from the Univer sity of Illinois to the Symposium, and he responded by making an informal presentation on the topic of his research. We hope this feature will continue. Previous Symposia in the series were: DATE SPONSOR LOCATION CHAIRMEN September 18-20 Gaithersburg, R.K. Kirby Natl. Bureau of 1968 Maryland Standards P.S. Gaal Westinghouse Astronuclear Lab. June 10-12 Santa Fe, R.O. Simmons Materials Res. Lab."

This book is t~e fifth in aseries of scientific textbooks designed to cover advances in selected research fields from a basic and general view point. The reader is taken carefully but rapidly through the introductory material in order that t~e significance of recent developments can be understood with only limited initial knowledge. The inclusion in the Appendix of the abstracts of many of the more important papers in the field provides further assistance for the non-specialist, and acts as aspringboard to supplementary reading for those who wish to consult the original liter ature. Surface analysis has been the subject of numerous books and review articles, and the fundamental scientific principles of t~e more popular techniques are now reasonably weIl established. This book is concerned with the very powerful techniques of Auger electron and X-ray photoelectron spectroscopy (AES and XPS), with an emphasis on how they may be performed as part of a modern analytical facility. Since the development of AES and XPS in the late 1960s and early 1970s there have been great strides forward in the sensitivities and resolutions of the instrumentation. Simultaneously, these spectroscopies have undergone a veritable explosion, both in their acceptance alongside more routine ana1ytical techniques and in the range of problems and materials to which they are applied. As a result, many researchers in industry and in academia now come into contact with AES and XPS not as specialists, but as users.

I express my full indebtedness to all researchers whose work is referenced in this book. Without their outstanding contributions to knowledge, this book would not have been written. I convey my thanks to Professor D. R. Axelrad (McGill University), who was the first person to introduce the fascinating subject of rheology to me and to Professor J. T. Pindera (University of Waterloo) for his kind encouragement and stimulating discussions on the subject matter. I am indebted to Dr J. H. Gittus, Editor-in-Chief Res Mechanica, for originally inviting me to write a book on viscoelasticity. of Permission granted to the author for the reproduction of figures and/or data by the following scientific societies, journals and publishers is gratefully acknowledged: Academic Press, American Chemical Society, American Institute of Physics, British Textile Technology Group, Elsevier Applied Science Publishers, Gebriider Born traeger, Helvetica Chimica Acta, Hermann, International Union of Crystallography, John Wiley & Sons, Pergamon Press, Springer-Verlag Heidelberg, Steinkopff Verlag, Tappi Journal, Taylor and Francis Ltd . . and the Institute of Physics. In the same context, the author wishes to express his sincere thanks and gratitude to Professors M. F. Ashby (University of Cambridge, United Kingdom), N. Davis (The Pennsylvania State University), H. F. Frost (Thayer School of Engineering), F. A. Leckie (University of Illinois at Urbana-Champaigne), E. H. Lee (Stanford University), J. M. Morrison (AT & T Bell Laboratories), A. K. Mukherjee (University of California, Davis) and Dr H. J. Sutherland (Sandia National Laboratories)."

Lo, soul! seest thou not God's purpose from the first? The earth to be spann'd, connected by net-work From Passage to India! Walt Whitman, "Leaves of Grass", 1900. The Internet is growing at a tremendous rate today. New services, such as telephony and multimedia, are being added to the pure data-delivery framework of yesterday. Such high demands on capacity could lead to a "bandwidth-crunch" at the core wide-area network resulting in degra dation of service quality. Fortunately, technological innovations have emerged which can provide relief to the end-user to overcome the In ternet's well-known delay and bandwidth limitations. At the physical layer, a major overhaul of existing networks has been envisaged from electronic media (such as twisted-pair and cable) to optical fibers - in the wide area, in the metropolitan area, and even in the local area set tings. In order to exploit the immense bandwidth potential of the optical fiber, interesting multiplexing techniques have been developed over the years. Wavelength division multiplexing (WDM) is such a promising tech nique in which multiple channels are operated along a single fiber si multaneously, each on a different wavelength. These channels can be independently modulated to accommodate dissimilar bit rates and data formats, if so desired. Thus, WDM carves up the huge bandwidth of an optical fiber into channels whose bandwidths (1-10 Gbps) are compati ble with peak electronic processing speed.