Harnessing Light Optical Science and Engineering for the 21st Century (1998) / Chapter Skim
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1 Optics in Information Technology and Telecommunications
1 Optics in Information Technology and Telecommunications
Pages 29-82
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From page 29... ...
The information age has recently been called the "tera era" because its technology demands are terabit-per-second information transport, teraoperations-per-second computer processing power, and terabyte information storage (see Box 1.1~. Because of the growing importance of image and video information, there is also demand for 300 ~ 250 - FIGURE 1.1 The growth of / the Internet and the World 200 - / Wide Web is among the fac o / tars driving the growth of 150 - / information technology.
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From page 30... ...
One of them is information transport over long distances, through large networks under the ocean, across continents, and in the local networks of the telephone and cable television systems. For this, optical fiber transmission is already the technology of choice, with a clear edge in cost and performance over competing technologies such as coaxial cable or satellite communications.
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From page 31... ...
A few rather obvious but critical points about high-tech mass markets and lowcost manufacturing shou Id be more widely understood and appreciated. They clearly apply to the mass markets for optical information technologies: C h a p t e r 1 BOX 1.2 ENABLING PHOTONIC DEVICES FOR PRESENT AND FUTURE LIGHTWAVE LONG-HAUL SYSTEMS Semiconductor lasers High-power pumps for fiber optical amplifiers Integrated laser-modulator transmitters Multiwavelength transmitters Tunable transmitters Soliton sources Semiconductor optical amplifiers Power amplifiers in integrated transmitters 1.3-,um optical amplifiers Optical switches and switch arrays Wavelength converters and other nonlinear functions Photodetectors and OEIC receivers High-speed (>10 gigabit-per-second [Gb/s]
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From page 32... ...
As a result, more than 90% of the manufacturing of these high-tech, mass market products now occurs offshore. At least four emerging optical information technologies fiber to the home, optical data links, small and miniature displays, and projection displays have an excellent chance of creating global mass markets in the not too distant future that are similar in magnitude to the three listed above.
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From page 33... ...
Note that a single fiber cable typically contains 20 to 40 optical fibers. (Courtesy of T
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From page 34... ...
Recent progress includes the development of optical fiber amplifiers! wavelength division multiplexing technology, photonic integrated circuits, and video compression.
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From page 35... ...
/ /0 ~1 80 82 84 86 88 90 92 94 96 98 Year FIGURE 1.3 A technology roadmap for lightwave systems, showing the transmission per fiber achieved in leading long-distance optical fiber systems over the past 15 years. The graph also indicates the progression of technologies developed for this accomplishment.
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From page 36... ...
Terrestrial Systems Optical fiber systems for long-distance transmission on land (also called "bunking") provide the links between metropolitan telephone offices, between cities, and across the continent.
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The bit rate of the optical signal stream in each fiber is 280 megabits per second (Mb/s) , and the typical regenerator spacing is 70 km.
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From page 38... ...
. WDM is a multiwavelength technique that increases the number of digital information channels that can be sent over a fiber simultaneously by transmitting each channel on its own distinct optical wavelength, as described in the section "Optical Networking and Switching" below.
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From page 39... ...
and SDH (STM-1 6) Transmission equipment only Lig htwave: ~20% Electron ics: ~80% $2 billion $2.5 billion $2 billion $4 billion NOTE: SONET = Synchronous Optical Network, SDH = Synchronous Digital Hierarchy.
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From page 40... ...
The advantages of completely replacing metallic telephone and cable television cables with fiber were recognized in the 1 970s. Numerous trials in Japan, Europe, Canada, and the United States, in both the telephone and the cable television industries, established the tech n ical feast hi I ity, but the costs for either repl acement or new construction were prohibitive.
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From page 41... ...
ONU Copper Pair it. ~ ~ ~3 1 x 16 Typical Fiber data channels, and is very similar to the technology used by the cable television industry.
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From page 42... ...
. Fiber's success in the cable television industry arises from the fact that a single analog lightwave system with only two active components a transmitter and a receiver can replace a trunk coaxial cable with 12 to 30 active trunk amplifiers while providing better end-of-line performance.
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From page 43... ...
As cable television operators look to enter the telephony and data network market, they are installing fiber ring architectures that improve the reliability of their networks. The arrival of digital television channels, such as those used by the DBS providers, breathes added life into the analog lightwave industry.
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From page 44... ...
, more sophisticated techniques are needed. In some respects, optical fiber is the only medium that can transport millimeter waves over any appreciable distance, because the attenuation of free space for millimeter waves is very large compared with the attenuation of fiber.
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From page 45... ...
Significant weight, power, and size advantages are realized over RF systems of similar performance, especially at very high data rates. However, optical space communications is still an emerging technology, with a checkered history.
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From page 46... ...
In these applications, light performs functions that cannot be done by electronics. By contrast, for most applications in information processing, electronic technology is excellent and sets a high standard of performance.
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From page 47... ...
This section describes optical information processing technologies from the most advanced to the most speculative. Optical Data [inks Optical fibers are an excellent transmission medium and, as seen in the first section of this chapter, they reign undisputed in long-distance transmission links.
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Optical data links have shown modest market penetration, with copper .
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From page 49... ...
Since transmission cost is falling exponentially, the primary system cost will be in switching and networking, unless network architectures change to use longer spans of fiber between switches. The current practice is electronic switching, in which a transceiver detects optical signals and electronic logic sends them where they C h a p t e r 1 FIGURE 1.9 The Optoelectronics Industry Development Association (OIDA)
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From page 50... ...
This keeps signals optical throughout switching and routing, and it avoids expensive optical-electronic conversions. In essence, it provides "transparent pipes" that enable transmission of any bit rate, any packet length, any transport format, and any modulation format including SONET (Synchronous Optical Network)
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From page 51... ...
WDM Networks In a WDM network, the use of many wavelengths permits huge network capacity, and the technology is scalable, modular, evolvable, and reconfigurable. WDM is economically viable because successful optical fiber amplifiers have been developed that can simultaneously amplify a large number of channels of different wavelengths without cross talk or interference with one another.
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From page 52... ...
and ACTS (Advanced Communications Technologies and Services) and are well coordinated, BOX1.5 WORLDWIDE PROGRAMS ONWDM NETWORKING There are several major optical networking programs under way worldwide.
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The third project is the MONET (Multiple Wavelength Optical Networking) consortium to determine the commercial feasibility of transparent optical networks, introducing a prototype network control and management system.
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From page 54... ...
Issues that cause difficulties for all-optical switching systems are synchronization and clock recovery, buffering and memory, and logic. In addition, ultrafast optical switching devices require too much power, l l H A R N E S S I N G L I G H T
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From page 55... ...
C h a p t e r 1 The existing technologies for high-density optical interconnects are in the form of optical data links, with multimode vertical cavity surface emitting lasers (VCSELs) or arrays.
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From page 56... ...
an SLM. For this step, traditional liquid crystal SLMs are seeing competition from magneto-optic and electro-optic semiconductor SLMs, which can be faster.
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From page 57... ...
Potential image processing applications lie particularly in rare-event problems, which electronic computers find difficult, such as fingerprint identification or recognition of a face in a crowd. Examples include electro-optic SLMs and smartpixel arrays (based on semiconductor multiple quantum wells, liquid crystals, or magneto-optics)
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From page 58... ...
Intellectual property concerns may currently be a barrier to this in the United States. Optical information processing faces some grand challenges: cost reduction of optical and optoelectronic components, packaged subsystems, and full systems; seamless merging of optics and electronics; optoelectronic device development driven by systems needs and system design driven by device realities; and full exploitation of wavelength, space, and time with optics.
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From page 59... ...
. Magnetic disk storage, the cornerstone of the industry, is characterized by its storage density.
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From page 60... ...
Today, CD-ROMs have already replaced floppy disks as the preferred medium for mass distribution of programs, video games, FIGURE 1.13 Dramatic cost reductions and performance improvements continue to bring the world of comput ers and the world of con sumer electronics closer and closer. The opticalcompact disk has had a powerful impact on the merger of these two worlds.
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From page 61... ...
Rewritable means that previously stored information can be erased and new information stored.) This trend toward erasibility and higher storage capacity would move optical storage into competition with high-end magnetic storage, but optical storage density is not increasing on the same steep slope as magnetic storage density.
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From page 62... ...
phase change NOTE: CD = compact disk, DVD = digital versatile disk, R = recordable, RAM = random-access memory, ROM = read-only memory, RW = read-write; dl = double-layer, ds = double-sided, sl = single-layer, ss = single-sided.
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From page 63... ...
Key Unresolved Issues What is u n resolved, of cou rse, is how far conventional optical storage density can be pushed and whether the cost-performance trade-offs will permit it to be more competitive with magnetic recording or rele gate it to niche markets. The former question is a concern of optics and recording physics; the latter relates to manufacturing and the market.
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From page 64... ...
To accomplish the former, resolution must approach the diffraction limit or, where possible, exceed it. Since the recorded spot size is directly proportional to the wavelength of the laser source and inversely proportional to the numerical aperture of the focusing objective lens, changing the wavelength and the numerical aperture are two high-leverage approaches to increasing capacity.
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From page 65... ...
To achieve these densities requires placing an element such as a glass hemisphere or a drawn fiber tip in close proximity to the recording layer, usually flying over it at distances less than C h a p t e r 1 FIGURE 1.16 Illustration of paths to higher optical storage density, including the use of shorter-wavelength sources (e.g., blue lasers) , increasing the numerical aperture of the objective lens, the use of multiple data layers, and the use of the third dimension (via holography)
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From page 66... ...
Another method of increasing effective storage density is to use multilayers data layers separated by thin transparent spacers or air gaps. The high numerical aperture of the focusing objective ensures that there is minimum cross talk between layers as close as 1 0 or 20 microns.
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From page 67... ...
The Defense Advanced Research Programs Agency (DARPA) should establish a program to seek new paradigms in optical storage that will reach toward the theoretical storage density limit of about 1.0 terabyte (TB)
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From page 68... ...
The history of liquid crystal displays (see Box 1.6) reminds us that many early innovations in this field started in the United States and Europe.
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From page 69... ...
The advent of the liquid crystal display has changed the CRT's domi nance of the display market. There are now two dominant mass display market segments: medium-sized displays (about 1 0.4 to 1 2.1 inches along the diagonal)
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From page 70... ...
Instead, by 1 991, Japan had the largest share of a hi 11 ion-dol lar LCD market. The subsequent development of activematrix liquid crystal displays (AMLCDs)
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From page 71... ...
There is also a strong thrust to develop electroluminescent displays and other potential breakthrough technologies, including liquid crystals on si I icon reflection-mode displays, digital micromirrors, and mirror-grating displays. There is no clear winner yet in the race to produce a highquality miniature display for the kinds of applications listed above.
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From page 72... ...
. plays is in flat, light, low volume visualinterfaces for Projection Displays personaldigitalassistants, Projection displays can be considered a close relative of the slide Web browsers, augmented projector.
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From page 73... ...
This could provide the catalyst and basis for U.S. reentry into the commercial and consumer markets, particularly if niche markets show fast growth and become mass markets.
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From page 74... ...
These programs are concentrated on CRT, plasma, electroluminescent, field emission, and liquid crystal technologies. There is widespread consensus that the U nited States shou Id try to reenter the mass display markets.
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From page 75... ...
The technology for analog lightwave transmission is improving rapidly and is enabling systems of lower cost and improved performance. Th is progress is broaden i ng the range of appl icabi I ity from cable television distribution to remote links for mobile radio cellular systems, as wel I as microwave and potential Iy mi 11 imeter-wave systems.
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From page 76... ...
Processing Data Links Low-cost optical data links are on the verge of becoming practical in local area networks that link together personal computers and workstations, file servers, printers, and data storage systems within computing clusters. To date, however, optical data links have achieved only modest market penetration, since copper is usually cheaper.
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From page 77... ...
Breakthrough technologies wi 11 be required before general-purpose optical computing is likely to be important. Applications for optical processing are in correlators and niche applications for machine vision and pattern recogn ition.
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From page 78... ...
Optoelectronic device development should be driven by systems needs, and system design by device realities. Designers of optical information processing systems shou Id more fu I Iy exploit wavelength, space, and ti me.
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From page 79... ...
Most R&D on three-dimensional storage is performed in the United States; although many of the programs are exploratory and some have stopped short of fruition, two major industry-university con sortia are in place to commercialize holographic recording. The unique requirement of specific market segments for systems with special performance characteristics is a driving force that will allow optical storage products to penetrate niche markets.
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From page 80... ...
Major change is transforming the display market and creating new opportunities for innovation. Once dominated by the CRT, the market is now split into two mass markets of about $20 billion each, plus a few niche markets.
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From page 81... ...
generated by the mass market heavy Japanese and Korean investment in low-cost manufacturing technology Is expected to result In Improved performance while lowering prices by at least 20% per year it will be extremely difficult to displace liquid crystals from the mass market for medium-sized flat-panel disolavs.
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From page 82... ...
The strategy should consider, among other options, U.S. mass market reentry via current market niches (e.g., very small or very large displays)
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