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Executive Summary Photonics is concerned with the use of photons to work with or to replace electrons in certain communications, computer, or control applications tradi- tionally carried out by electronics. It is a key high-technology area, well es- tablished in long-distance fiber-optic telecommunications and rapidly growing in other areas of great importance to society. In this report the panel has concentrated on technical areas where the overall worldwide market for equip- ment approaches $400 billion per year. After reviewing the present status of each of these areas of technology, the panel identifies some of the key enabling technologies needing development or research. Because of the intense interna- tional competition in photonics, more general policy issues and recommenda- tions aimed at strengthening the U.S. position in this industry are included in a final chapter. TELECOMMUNICATIONS The worldwide market in telecommunications equipment exceeds $100 billion per year. Fiber optics is firmly established for long-distance and moder- ate-distance point-to-point applications because of the large information capacity, the greater distance between repeaters, and the freedom from electrical interference. Starting with 800- to 900-nm (nanometer) light and multimode fibers in the 1970s, it has passed through three generations to 1300 nm light and single-mode fibers, with work toward 1500-nm light for the future. Enabling technologies identified as ripe for development include items related to fiber cables, high-performance transmitters, improved receiver modules, and 1
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2 PHO TONICS several critical passive components. (For a full list with explanation, please see the section on "Enabling Technologies" ~ Chapter 2.) Technologies needing continuing research include coherent communication systems, components for wavelength-division multiplexing, low-noise avalanche photodiodes, optical amplifiers, external modulators, fibers with low loss and low dispersion over extended bandwidths, and practical integrated optics technologies. Much of the potential for future growth of fiber optics will come from local area networks, metropolitan area networks, and broadband integrated service digital networks. Needed developments for these fields must stress low cost and high reliability, with emphasis on easy access to the fibers and rapid movement toward mono- lithic integration. Continuing research is needed on optical switching compo- nents, optical amplifiers, and monolithic integration of both optical and electronic functions. Studies of network architectures are needed to make full use of the capabilities of photonic networks. Improved performance materials are also needed. Military applications for optical communications will require progress in all of these areas, with emphasis on high performance, resistance to radiation, and ruggecli~ntion. INFORMATION PROCESSING The market for information processing is also estimated at $100 billion per year worldwide and is predominantly electronics. Photonics offers the potential advantages, for both analog and digital applications, of almost limitless bandwidth, immunity from electromagnetic interference, and the easy use of side-by-side channels. These advantages have been used in synthetic aperture radar and other military analog applications and in commercial laser printers and scanners. Research and development needs for analog photonic systems include high-performance spatial light modulators, improved materials, and development of integrated optics modules. The present use of photonics in digital information processing is largely in the interconnections: computer to computer, and computer to storage input/output device. In this application area, computer systems are migrating from centralized single-processor centers to distributed multiprocessor complexes, including clusters of high-speed workstations. The interconnection network becomes a critical component in the performance of such a complex. High speed, high packaging density, and high reliability photonics--compatible with the electronic integrated circuit technol- ogy used in computers--has yet to be developed. Early technology connected box to box, with a potential for connection technology to go to board-to-board and chip-to-chip connections, where congestion in communication lines can limit system performance. For hardware implementation, hybrid approaches to integration of the electronic logic and the photonic interconnects are promising for the near term,
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EXECUTIVE SUMMARY 3 but monolithic integration is desirable for the long term. Work on hetero-epi- ta~nal materials, such as gallium arsenide (GaAs) on silicon (Si), is needed, and free-space interconnections should be investigated. There is much present interest in the question of all-photonic digital computation because of the fast response of optical devices, but this is still very much in the research stage. Research is needed on materials with larger optical nonlinearities, on new algo- rithms, and on new architectures to match the special characteristics of optical logic elements. Optical neural networks are being investigated as one approach to such architectures. OPTICAL STORAGE AND DISPLAY On-line, rapid-access storage is currently dominated by magnetic storage media and is a more than $50 billion per year industry. The archival storage industry is even larger, so that the information storage application is likewise greater than $100 billion per year. Optical storage media offer higher density storage by a factor of 500 times or so and thus offer potentially lower cost. Optical storage has been developed for archival storage where the information is written once by the user but can be read many times, and for read-only stor- age where replicas of a master disk are distributed to users. Optical storage for the multiple read and write system is only now beginning to be marketed. Japan is dominant in each of these technologies. A particularly promising application of optical storage is for an "interactive encyclopedia" in which a stored subject consists of words, pictures, and video movies to fully describe the subject. Enabling technology needs for optical storage include higher power lasers or laser arrays for the read/write heads, low-mass read/write heads, multiple- track reading and multiple-platter systems, and development of planar, self- aligned optical and optoelectronic elements for ease of manufacture. For the read/write applications, better reversible high-contrast materials are needed. Long-term research is especially needed on the reversible materials and on laser sources. Displays convert electronic information to images and text for human view- ing. The market of about $8 billion per year is dominated by cathode-ray displays, with plasma panel displays and electroluminescent panels also important. Photonic displays are those addressed by light beams, as when a laser writes on a liquid crystal cell. Such displays may have specialized uses but are not likely to displace existing electronic display technologies in the foreseeable future. Research should continue on new materials and new systems concepts that might lead to superior display technologies in the future. Multiple-beam addressing systems, the incorporation of holograms for three- dimensional displays, and improved resolution materials are some of the directions for such research.
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4 PHO TONICS OPIICAL SENSORS Although the sensor market is modest ($3 to 5 billion per year) and highly fragmented, sensors provide the critical enabling technology for many large systems. Photonic sensors include f~ber-optic sensors and focal plane arrays (FPAs). The former have been developed for sensing of temperature, pressure, displacement, magnetic fields, and other physical or chemical environmental parameters. They are accurate, can operate in harsh environments, and are compatible with optical telemetry. High-performance fiber-optic hydrophores, gyros, and magnetometers have been demonstrated for military applications. The barrier to increased use does not seem so much the development of appropriate technology as a need for standardization and demonstration of the advantages of well-engineered all-optical systems based upon these sensors. Focal plane arrays using primarily charge coupled and charge injection device concepts have, in the last two decades, led to a revolution in data handling and processing of radiation-induced signals in the infrared and visible regions. They have been used in strategic and tactical military applications, ecologic monitoring, and such consumer applications as the miniature video camera. Although there is reasonable control over device parameters in visible spectrum FPAs using Si, there is more nonuniformity in the infrared (JR) devices using indium antimonide (InSb) and HgCdTe material systems. Con- tinued research is needed on materials, interface improvements, and fabrication yield. Equally important is the need for software to support FPA data ac- quisition and processing. The long-term goal should be the development of algorithms and processors to permit the processor to fit in a volume comparable u ith that of the sensor unit. POLICY ISSUES Although much of the research in photonics was done in the United States, there is tremendous international competitiveness in developing high-quality, low-cost products; Japan is the leader in many fields. There have been many government and National Research Council (NRC) studies of the competitive- ness issue (see Appendix C), and it is clear that much needs to be done if the United States is to maintain its competitive position in this and other high-tech- nology areas. The greatest burden for responding to the challenge falls on industry. The federal government also has a role to play. The panel addresses the following suggestions to industry: ~ It is essential to increase our industrial competitiveness in product development, manufacturing skills, and marketing.
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EXECUTIVE SUMMERY s ~ There must be continuing industrial effort in long-range research and innovation. ~ The photonics industry should consider the advantages of an industry association that could help organize consortia to conduct cooperative research and address technical problems and policy issues beyond the scope of any one organization. · Government contractors who receive a percentage of sales for their in- dependent research should devote a sizable fraction to projects with a life span of 5 to 10 years. meet: The panel addresses the following recommendations to the federal govern- · Government should play a more active role in assessing technological opportunities and catalyzing development of technology in industry. Considera- tion should be given to a national photonics demonstration project. Federal support for research and innovation in photonics should continue. ~ Regulation, antitrust, and tax policies must be considered carefully as they relate to industrial investment in the transfer of technology from research, in the development of manufacturing processes for low-cost/high-volume production, and in providing new services. It is important that there be high-quality education In this important field and specialized equipment for universities active in photonics. In view of the expense of obtaining and operating such equipment, the panel recommends shared use of existing molecular-beam epitaxy (MBE), metallo-organ~c chemical vapor deposition (MOCVD), and other specialized microfabrication equipment. This should be encouraged by a variety of incentives, e.g., tax credits and supple- mental grants. When requests for new units do appear to be justified, it should be determined that the institution is being realistic regarding the source of funds for proper operation of the equipment. Additional postdoctoral positions in the national laboratories should be established.
Representative terms from entire chapter: