Optics and Photonics Essential Technologies for Our Nation (2013) / Chapter Skim
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3 Communications, Information Processing, and Data Storage
3 Communications, Information Processing, and Data Storage
Pages 64-101
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From page 64... ...
One key driver for such shorter distances will be to attain sufficient density of communications. A second key driver will be to control the growing power dissipation that is due to switching/transmission elements and the environmental impact of information processing.
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From page 65... ...
For the future there are expectations that this growth will con tinue as more video content calls for bandwidth and that there is a need for another factor-of-100 growth in the coming 10 years as well. Major advances have also been achieved in both cost-effectively managing the large capacity in today's WDM optical networks and in leveraging the value propo sition of optical amplifiers to provide multi-wavelength amplification over network mesh and ring architectures.
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From page 66... ...
WDM optical networks require reconfigurable optical add/drop multiplexers (ROADMs) to, under network electrical control, drop or add wavelength chan nels at a node and to switch wavelength channels from one fiber route to another.
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From page 67... ...
It ranks roughly at number 11 among the countries in the world, with approximately 7 percent penetration. The penetration of fiber to the home in the United States is roughly 5 percent.4 Passive optical networks (PONs)
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From page 68... ...
As a result, optical networks that underpin the Internet have been able to keep pace with exploding demand over the last 10 years. How ever, realistically, the several-orders-of-magnitude capacity increase resulting from many wavelengths will not be duplicated by simply adding even more wavelengths, because of limited optical amplifier bandwidth and fiber power limits in the fiber to mitigate transmission impairment.9 8 National Research Council.
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From page 69... ...
Information Processing The main, and growing, use of optics in information processing is to connect information within and between information switching and processing machines. There are substantial physical reasons -- specifically, reducing power dissipation and increasing the density of information communications -- why optics is preferable and ultimately possibly essential for such connections.10 The idea of using optics for performing the logical switching in information processing -- as in some kind of optical transistor -- is one that has continuing research interest, although the criteria for success there are challenging,11 and no such use appears imminent.
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From page 70... ...
optical fibers for the shorter distances. The use of optics in such networks is likely to steadily increase because of continuing increases in network traffic and information processing.
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From page 71... ...
Electricity used in data centers in 2010 likely accounted for between 1.1 and 1.5 percent of total electricity use globally, and between 1.7 and 2.2 percent of electricity use in the United States.20 The power dissipation in interconnects in serv ers alone has been estimated to exceed solar power generation capacity.21 Of course, information processing and communication can have substantial environmental benefits in improving the efficiency of many activities and in reducing travel.22 But, if current growth trends in Internet traffic and in information processing continue, reducing the energy per bit processed and/or communicated will be crucial. Even though sending a bit over the Internet might take approximately 10 nanojoules (nJ)
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From page 72... ...
New technologies have been advancing in research and early product intro ductions over the last decade, especially in terms of devising ways of combining optics, optoelectronics, and electronics in silicon chips and platforms (silicon photonics) .27,28 These technological opportunities are discussed below.
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From page 73... ...
Initially the Internet was not reliant on optical communications. However, data transfer rates during those formative times were painfully slow.
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From page 74... ...
Telecommunications research has yielded major benefits such as the Internet, radio frequency wireless communications, optical networks, and voice over Inter net Protocol. Promising opportunities for future research include enhanced Internet architectures, more trustworthy networks, and adaptive and cognitive wireless net works.31 The 2002 NRC study Atoms, Molecules, and Light: AMO Science Enabling the Future stated: Internet optical backbone link capacity increased a hundredfold between 1995 and 1998, to 20,000 trillion bits per second.
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From page 75... ...
However, the research community is struggling to envision technical paths for achieving this vision. In the mid-1990s, leading laboratories achieved the transmission of 1 Tb/s and 0.1 Tb/s respectively over hundreds and thousands of kilometers of single-mode optical fiber.37 The key advances that enabled these results and that were captured by the NRC's 1998 Harnessing Light38 study include those described below.
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From page 76... ...
2008. Optical Fiber Telecommunications V B: Systems and Networks.
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From page 77... ...
of 16 to 512,44,45,46 as seen in Figure 3.2, in which data are encoded on both phase and amplitude of the optical carrier. Additionally, independent data can be transmitted along the two orthogo nal polarization axes of the optical fiber, that is, polarization-division-multiplexing, doubling again the capacity and spectral efficiency.47 Coherent Systems Utilizing Digital Signal Processing.
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From page 78... ...
a special multi-core fiber, each individual core of which transmits an independent data stream;51 and (2) a few-mode fiber, with each independent data channel on one of the orthogonal spatial modes (see Figure 3.3)
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2012. Mode-division multiplexing over 96 km of few-mode fiber using coherent 6×6 MIMO processing.
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European Conference and Exposition on Optical Communications. Available at http://www.optics infobase.org/abstract.cfm?
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IEEE Journal of Selected Topics in Quantum Electronics 17(6)
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From page 82... ...
This scenario has benefited greatly from advances in photonic integrated circuits on both III-V68 and silicon materials.69 Optical Fiber Modifications. Although the attenuation of optical fiber reached its near-optimum point of 0.2 decibels per kilometer (dB/km)
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From page 83... ...
Moreover, it has been well known that although electronic power consumption scales with increased data rate, the power consump tion of photonics does not. In view of both of these facts, the optical communications community is taking very seriously the mantle of using optics in novel ways to dramatically reduce the power consumption.
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FIGURE 3.5 (a) Intel creates the world's first end-to-end silicon photonics connection with integrated lasers.
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Optical Fiber Communication Conference (OFC) , Los Ange les, Calif., March 6, 2011.
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An exciting area of R&D is in passive optical networks, such that gigabits per second data rates can be deployed at low cost to many simultaneous users in a neighborhood.87 Advances in low-cost integrated optical components and efficient optical access architec tures will be crucial to achieving this vision; note that RF-over-fiber, in which a radio-frequency subcarrier is encoded and is transmitted on an optical carrier wave, represents an interesting and potentially exciting approach to bridge the gap between wireless signals and WDM networks.88 It should be emphasized that the exponential growth in wireless traffic only accelerates the need for optics in access networks, since wireless hubs will typically connect in the ground to the larger network through optical fiber. Clearly, the optics and photonics community needs 83 Lewotsky, K
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From page 87... ...
Brief descriptions of example areas of R&D that have the potential for large impact include the following: · Quantum communications. Quantum optical communications typically use the quantum state of a single photon or a pair of entangled photons -- which can be widely separated while maintaining their inherent quantum connection -- in order to achieve ultimately secure and highly efficient com munications.89 For example, if information is encoded on the photon's state of polarization (SOP)
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From page 88... ...
Evolutionary Progress in III-V Device Technology Technology for optical data links continued to evolve in the last decade, with continued improvements in speed and reduced power dissipation for device tech nologies such as VCSELs. Integration of devices in larger functional units has con tinued in III-V technology.93 Such predominantly III-V approaches can integrate multiple active optoelectronic devices, such as lasers, optical amplifiers, modula tors, switches, and detectors for highly functional units for optical networking.
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From page 89... ...
Ring resonators are still largely in research, in part because of the requirements for precise tuning and thermal stabilization. Most silicon photonics work is targeted at the telecommunications wavelengths (e.g., in the so-called C band near 1550 nanometers [nm]
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From page 90... ...
Ap proaches exist for hybridizing III-V materials onto silicon substrates and/or optical structures, and such approaches offer one intermediate approach for integrating light sources on the chip. However, amplifiers on the chip may be very desirable in order to increase functionalities, given that the Si-based optical components are still fairly lossy, which limits the number of components that can be integrated.
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From page 91... ...
that often limit more conventional approaches to device fabrication.106 As the size of many of these new optics and photonics elements shrinks, it certainly opens up for the possibility to produce systems that utilize the best of optics and electronics to enable integrated systems to seamlessly provide solutions in many of today's fields. Data Storage The advent of nanometallic structures to concentrate light to deeply sub wavelength volumes has opened up new opportunities for optics in data storage, both for sub-wavelength optical reading and writing and for the use of optics to concentrate light for other storage approaches, as in heat-assisted magnetic recording, whereby the light provides the very localized heating above the Curie temperature to enable correspondingly localized changes in magnetic state.
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From page 92... ...
These optical systems and network ele ments are assembled from optical modules (for example, optical transmitters and receivers) that in turn are built from optical components, including lasers, optical modulators, photodetectors, optical fiber amplifiers, and others.
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From page 93... ...
Optical components for communications networks still involve several t echnologies -- indium phosphide (InP) , CMOS, lithium niobate, and silica.
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From page 94... ...
At this time, beyond the strong possibilities in HAMR and some continuing use of optical disks such as DVDs, the path for other optical data storage approaches is less clear, although there is continuing development of holographic storage for commercial archiving, with possible capacities in the 500 Gb to 1 Tb range in a disk of a size comparable to that of current DVDs.113 Other approaches remain in research at the present. ECONOMIC IMPACT Communications networks have taken on a role well beyond people-to-people voice communications; they provide the information and trade routes of the new global digital economy.
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From page 95... ...
Its paper submissions to international optics journals and to the premier global optical communications conferences have increased substantially in the last 5 years.115 There is particularly strong research in Europe and recently also in Japan in the emerging silicon photonics platforms for networks and interconnects. Given that labor-intensive industries will continue to migrate their manufac turing to low-labor-cost regions, it is imperative that the United States stay at the leading edge of optical technology at the component, platform, and system levels.
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From page 96... ...
The United States lacks the larger European framework projects that help tie together a broad range of players from academia to industry. Both Europe and Japan are making substantial investments in silicon photonics technology research now.
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From page 97... ...
China is poised to make great strides in the coming decade. FINDINGS AND CONCLUSIONS In spite of great progress in optical communications over the last three decades, the optics and photonics community faces a great challenge if optical communica tions networks are to continue to satisfy the insatiable global demand for informa 116 The selected journals were these: Optics Communications, IEEE Photonics Technology Letters, Op tics Express, Journal of Lightwave Technology, Optical Engineering, Microwave and Optical Technology Letters, Journal of Optical Communications, Physical Review A Atomic Molecular and Optical Physics, Optics Letters, Photonic Network Communications, Applied Optics, Applied Physics Letters, Journal of the Optical Society of America B Optical Physics, Fiber and Integrated Optics, Optical and Quantum Electronics, Proceedings of SPIE the International Society for Optical Engineering, IEEE Transactions on Communications, IEEE Transactions on Microwave Theory and Techniques, IEEE Proceedings Optoelec tronics, Journal of Optical Networking, and Photonics Spectra.
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From page 98... ...
It is important to note that the previous 100-fold gain in capacity that came very naturally with wavelength division multiplexing has been used up; growth by means of higher bit rates per wavelength comes more slowly; hence without a new breakthrough, increases in data transmission capacity will stall. Key Finding: Cloud services not only drive capacity demand, but also make critical the role of large data centers.
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From page 99... ...
RECOMMENDATIONS AND GRAND CHALLENGE QUESTIONS Key Recommendation: The U.S. government and private industry, in combination with academia, need to invent technologies for the next factor-of-100 cost-effective capacity increase in long-haul, metropolitan, and local-area optical networks.
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government and private industry should position the United States as a leader in the optical technology for the global data center business.
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From page 101... ...
Recommendation: A multi-agency and cross-discipline effort is recommended to identify the opportunities and optical technologies to significantly increase the en ergy efficiency in communications networks, information processing, and storage. In addition, new ideas for the use of energy-efficient optical approaches to displace current energy-hungry practices -- for example, travel -- should be identified and supported.
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