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Nanophotonics Accessibility and Applicability Summary The purpose of this study, carried out by the National Research Council’s Committee on Nanophotonics Accessibility and Applicability, is to determine the accessibility of nanophotonics technology in a 10-to-15-year time frame, to identify the nations that control these technologies, and to review the scale and scope of offshore investments and interests in nanophotonics. Further, this study identifies feasible nanophotonics applications; their potential relationship to military systems; associated vulnerabilities of, risks to, and impacts on critical defense capabilities; and other significant indicators and warnings that can help prevent and/or mitigate surprise related to technology application by those with hostile intent. Finally, this report recommends priorities for future action by appropriate departments of the intelligence technology warning community (ITWC), the Department of Defense (DOD) research community, and other government entities. THE BOTTOM LINE The domain of nanoscale science and technology lies between the familiar classical world of macroscopic objects and the quantum mechanical regime of atoms and molecules. Nanostructures can have unique, controllable, and tunable optical properties that arise from their nanoscale size and from the fact that they are smaller than the wavelength for which they are designed. Both the properties of the nanostructures and their organization into large-scale materials, which may be ordered on the scale of the wavelength, are important for determining the optical response. Indeed, the optical properties of nanomaterials can be tailored for important commercial and defense applications, such as compact photoelectric power sources; efficient and tunable light sources, detectors, filters, waveguides, and modulators; high-speed all-optical switches; environmental (both chemical and biological) sensors; next-generation classical and quantum computation; and biophotonic medical diagnostics and therapeutics. This area of nanoscience, called nanophotonics, is defined as “the science and engineering of light-matter interactions that take place on wavelength and subwavelength scales where the physical, chemical or structural nature of natural or artificial nanostructured matter controls the interactions.”1 1 See http://www.phoremost.org/about.cfm. Last accessed April 9, 2007.
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Nanophotonics Accessibility and Applicability One-dimensional nanoscale structures, such as multilayer optical coatings and distributed Bragg reflectors, have long been staples of optical design and engineering. This report is restricted to the new developments that arise from the ability to control structures at the nanoscale in multiple dimensions (two-dimensional and three-dimensional photonic crystals, reduced dimensionality, and quantum confinement), to control both the magnetic and the electrical response of materials (metamaterials), or to manipulate nanoscale structures for enhanced field concentration (plasmonics). The areas of nanophotonics discussed in this report are characterized by their different physical nanoscale phenomena and the scale (relative to a wavelength) of the modulation of the index of refraction in the nanoscale material or system. Following are the four areas of nanophotonics selected by the committee as most relevant to cover in this report: Photonic crystals—in which the spatial index modulation is on the order of a wavelength; Metamaterials—in which the structural elements are much smaller than the wavelength, permitting an effective medium approach to the optical properties; Plasmonics—in which manipulation of light at the nanoscale is based on the properties of surface plasmons arising from metal free-electron response (negative permeability); and Confined semiconductor structures—whose physics is driven by reduced dimensionality and quantum confinement. ACCESSIBILITY The committee identified several overarching themes regarding the accessibility of nanophotonics technology in a 10-to-15-year time frame. First, nanophotonics will provide foundational building blocks for military capabilities, as discussed by the committee in addressing nanophotonics in relation to major strategic/critical military technologies. Second, advances in nanophotonics will enable new systems. A third theme noted by the committee is that of commercial markets pushing advances in nanophotonics to an increasingly greater degree while DOD and intelligence community agencies concurrently play lesser roles as drivers of this field. Specific technological advances in nanophotonics are expected to contribute to major scientific and applications developments. The following list of such innovations is representative, not exhaustive: The surmounting of optical wavelength limitations in electronic devices, allowing unprecedented resolution in imaging applications, as well as the true integration of photonic and electronic functionalities. Implications include the ability to truly realize “optics on a chip” through the combination of nanoelectronics and nanophotonics, enhancing a range of capabilities from information technologies and advanced computing to advanced sensing. Success in this area would also enable breakthroughs in imaging systems and microscopies where the diffraction limit to resolution will be overcome in many important cases. The confinement of optical-matter interactions to the nanoscale, where the quantum mechanical regime dominates interactions and yields size-dependent, novel electronic and optical properties. Progress in this area would enable a wide range of “quantum technologies” such as quantum computing, quantum cryptography for secure communications, and advanced sensing capabilities. Other applications include tunable and efficient light sources, detectors, and other optical elements with enhanced and reconfigurable functionality.
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Nanophotonics Accessibility and Applicability The ability to dramatically alter the optical properties of virtually any material by suitable combinations of “top-down” and “bottom-up” fabrication technologies, enhancing the capabilities for signaling, switching, detection, and concealment. Profound advances in the control of single photons, the increased efficiency of photonic devices, and the interaction of photons with matter have been realized over the past 15 to 20 years. The committee expects that the pace of innovation and implementation will only increase with the availability of novel nanophotonics building blocks, the development of enabling technologies, and the insights gained by characterizing nanophotonics devices and phenomena. APPLICATIONS Nanophotonics-based systems are expected to have far-reaching applications in both military and commercial markets, including the following: Power, weight, and volume savings with higher speed and functionality on all military systems, including but not limited to (1) uncooled, infrared sensors and night vision; (2) ultrasecure communications and quantum information processing; and (3) photovoltaic power sources; External photonic communications between nanophotonic-enabled silicon chips, with widespread application likely within a few years, particularly for computers and microprocessors; Internal photonic communication within chips, enabling militarily significant functions, such as (1) potentially significant power savings within computing systems and (2) multicore processor interconnects leading to advanced computational applications such as image recognition; Heat-assisted magnetic recording using plasmonic focusing, which is part of the roadmap of the hard-disk drive industry; and Biosensing systems based on fluorescent molecules and/or quantum dots and on plasmonic effects—for example, surface-enhanced Raman scattering—for use in medical in-field diagnostics, bioagent detection, and bioremediation. FOREIGN CAPABILITIES AND INVESTMENTS Very large, focused, and growing foreign investments are enabling significant research programs in nanophotonics overseas. These programs highlight the international scope and inherent complexities of nanophotonics research and development (R&D). They include the following: In Europe: Large, multicountry collaborations in plasmonics, metamaterials, and nanocavity quantum electrodynamics are being sponsored by the European Union. In Japan: Japan funds nanotechnology research primarily through its Ministry of Technology and its Ministry of Education. Researchers in Japan have made seminal contributions in the achievement of high-quality photonic crystal devices for low-threshold lasing, low-loss waveguiding, high-speed switching, all-optical circuit switching, and other applications. There is also forefront R&D in the areas of efficient optical sources, including quantum dot lasers and prototype nanophotonic devices. Finally, research on the theory of optical near-field interactions with nanomaterials is underway, and work is progressing toward the fabrication of prototype nanophotonic devices.
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Nanophotonics Accessibility and Applicability In China: China continues to make huge investments in education and research infrastructure. In the past 5 years (through 2006), the Chinese publication rate in areas related to nanophotonics has increased enormously. A closer inspection of the publication topics indicates a large proportion of research related to the simulation and modeling of nanophotonic structures and devices rather than to demonstrations of fabricated devices and systems. However, as the required experimental infrastructure is further developed and employed, advanced technological demonstrations of nanophotonic systems can be expected. A critical precursor technology, silicon integrated circuit planar fabrication, is already gaining a large foothold in China (JTEC, 1996). KEY FINDINGS In reviewing the global state of nanophotonics R&D, with a particular emphasis on military applications, the committee identified several key findings that have broad and critical implications regarding the accessibility and applicability of nanophotonics, as well as the importance of potential nanophotonics technologies to national economic and military security. These key findings, which are the basis of the committee’s recommendations, are presented below (with their position in the main text noted in parentheses) in the context of a necessarily abbreviated discussion reflecting the committee’s deliberations. More detailed justification of these findings and additional, more specific findings are contained in the body of the report. Because of its unique scale length at the interface between the quantum and the classical descriptions of matter, and because of the exceptionally wide range of materials and fabrication processes that have applicability, nanophotonics necessarily draws on a broad range of scientific disciplines. The uses of nanophotonics require additional expertise in devices and systems. Finally, manufacturing at the nanoscale is an emerging discipline that draws on many different fields. While there are many similarities with manufacturing for the electronics industry, nanophotonics involves a much wider range of materials, offering unique manufacturing challenges. Progress in nanophotonics, which is characterized by its interdisciplinary nature, requires significant teaming across many fields. Nanophotonics is a highly interdisciplinary field requiring expertise in many areas of materials science, chemistry, applied physics, optics, electrical engineering, systems engineering, and modeling and simulation, among other disciplines. (Finding 6-1) Traditionally, synthesis, growth, and fabrication have been separately identified stages in the development of functional devices. Thus, for example, in today’s electronics and photonics manufacturing, the preparation and growth of full-wafer epitaxial layers are performed before fabrication processes are used to define selected lateral areas for devices and related circuit elements. In the nanoscale era, these distinctions among synthesis, growth, and fabrication are blurring, and the steps are implemented in mix-and-match ways to produce novel functional nanostructured materials and to arrange them with the necessary hierarchical organization to produce new functionalities. Many researchers are investigating epitaxial growth on nanoscale areas, defined by some transverse fabrication before the growth process is initiated. Traditional electronic-device fabrication employs well-defined and largely separate stages of synthesis, growth, and fabrication. In contrast, the generation of nanophotonic materials and devices blurs these distinctions, and certainly the order of these stages, interleaving them in new and novel ways. (Finding 3-2)
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Nanophotonics Accessibility and Applicability Because of the evolving, interdisciplinary, and complex nature of nanosynthesis, growth, and fabrication, state-of-the-art capabilities to perform this R&D are becoming increasingly expensive, even prohibitively so. The wide range of materials involved in today’s nanoscience research and the need to avoid cross-contamination require multiple copies of expensive equipment, further compounding the cost issue. For example, gold is frequently needed for nanophotonics research, but it is anathema in any silicon (Si) fabrication facility because the fast diffusion rates of gold in Si affect doping and electronic device performance. Research institutions ranging from universities to industrial research laboratories to national laboratories are finding that building such facilities is often unaffordable, and that even maintaining existing facilities at the state of the art is becoming increasingly difficult to sustain. The necessary fabrication facilities are becoming increasingly expensive and difficult for U.S. research institutions to maintain. (Finding 6-2) The development of enabling technologies, along with significant infrastructure, will be essential for the implementation of commercial and military applications of nanophotonics. The essential enabling elements for nanophotonics include (1) synthesis, growth, and fabrication of nanomaterials and nanostructures; (2) characterization techniques for nanophotonics; (3) modeling and simulation; and (4) packaging and integration of nanophotonic devices. The presence of these enabling technologies in a country is often an important indicator of the state of maturity of nanophotonics in that country. However, because the approach to nanophotonics R&D is significantly more interdisciplinary and revolutionary than the current approach to photonics or microelectronics, countries with significant infrastructure in these traditional application areas will not necessarily dominate nanophotonics R&D. Other countries may emerge as leaders in nanophotonics based on initiatives that enable breakthrough technologies. At the same time, the accelerating diffusion of advanced manufacturing technologies for traditional electronics and photonics is enabling new opportunities for countries that have not heretofore had strong national efforts to establish R&D programs that will compete for the new possibilities enabled by nanophotonics. Developments in synthesis, growth, and fabrication for photonic nanostructures extend across a wide range of materials and techniques and follow nontraditional paths. While it is tempting to assume that those countries which today have an extensive infrastructure for traditional photonics and microelectronics will continue to be the dominant developers of this new technology, this infusion of new ideas and new technologies means that new players can emerge over the 10-to-15-year time frame covered by this report. (Finding 3-1) The globalization of science and technology, along with the increase in the quality of scientific institutions and universities abroad, particularly in Asia, is likely to diminish and even eliminate the scientific edge that the United States enjoys, particularly in emerging technologies such as nanophotonics. The globalization of expertise in nanoscale science and technology, as shown in part by the growth in publications in nanophotonics by researchers in countries such as China, will become increasing evident over the next decade and beyond. It is likely that certain foreign nations will have equal or superior technical capability in nanophotonics compared with that of the United States within the next 10 to 15 years. These capabilities include fabrication, design, and systems integration; fundamental research; and a trained and talented workforce and educators. (Finding 6-3)
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Nanophotonics Accessibility and Applicability The committee believes that there is clearly a potential for nanophotonics to have a significant impact on military systems for both symmetric and asymmetric warfare. It is also true that nanotechnology insertion into disruptive technologies that could pose threats is difficult to anticipate by the very nature of such threats and the sometimes embryonic state of research in nanophotonics relative to other technologies. Some applications may take substantial investments and time before they are realized. Moreover, the application of nanophotonics requires a fabric of supporting and enabling technologies. This technology environment (at least in part) does not exist today, which further complicates the outlook. Therefore, most applications of nanophotonics will yield evolutionary changes in the current state of military technology, both domestic and foreign. However, there is a small but finite chance of a possible “game changer” technology emerging from the realm of nanophotonics, particularly in the area of information technologies, where breakthroughs in nanophotonics R&D could potentially enable a much more ubiquitous and pervasive data processing (and sensing) capability than is currently available. The committee believes that, because of the infancy of nanophotonics, the probability of near-term revolutionary changes using nanophotonics is small but not negligible, for both domestic and foreign entities. (Finding 4-1) KEY RECOMMENDATIONS As a result of its study, the committee developed several key recommendations based on the key findings summarized in the previous section. These recommendations address the broad and critical implications regarding the accessibility and applicability of nanophotonics, as well as the importance of potential nanophotonics technologies to national economic and military security. These key recommendations are presented here, along with a necessarily abbreviated discussion of the committee deliberations. More detailed justification of these recommendations and additional, more specific recommendations are contained in the body of the report. In the context of globalization, it is folly to assume that the United States will lead in all technologies relevant to military applications. The trend toward globalization is believed by the committee to also hold true for nanophotonics. Nanophotonics components, modules, and subsystems will play a large role in future U.S. weapons systems. In order to have the best and most affordable weapons systems, some of the nanophotonics items used in future U.S. weapons systems will probably not be produced within the United States, as is now the case for increasing numbers of other technologies’ components, modules, and subsystems. This situation requires careful oversight and monitoring on the part of the ITWC. The committee recommends that the intelligence technology warning community establish, maintain, and systematically update and analyze a comprehensive array of indicators pertaining to the globalization and commercialization of nanophotonics technologies that would complement and focus intelligence collection on and analysis of the topic. This effort should have a strong focus on monitoring the developments of the technology in countries not predisposed to selling such technology for use in U.S. military systems. The intelligence technology warning community is advised to monitor those countries that have strong backgrounds in related technologies, integrated optics, semiconductor lasers, compound semiconductors, microelectronics, and nanoscale photolithography. (Recommendation 5-1) Consistent with current policies and practices, the United States has retained the domestic industrial capacity for specific strategic and critical military capabilities, including mid- and long-wavelength in infrared imaging; chemical and biological threat detection; secure communications (encryption, decod-
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Nanophotonics Accessibility and Applicability ing, electromagnetic eavesdropping); situational awareness; secure computing; electronics systems on weapons platforms; battlefield control; stealth; countermeasures—infrared and visible; weapons platforms; and nuclear weapons. The committee thus assumes that filling the need for these critical capabilities is not likely to be left to foreign industries. However, an up-to-date understanding of the evolving global situation in this arena is essential and requires constant, systematic monitoring. The committee recommends that the intelligence technology warning community monitor the worldwide development of nanophotonics technologies that have a high probability of impacting U.S. strategic and critical military capabilities, such as in mid- and long-wavelength infrared imaging systems, chemical and biological threat detection with compact and rugged instruments, secure communications, situational awareness, secure computing, enhancement of the electronics systems capabilities on U.S. weapons platforms, and enhancement of U.S. battlefield control capabilities. (Recommendation 6-1) Due to the highly interdisciplinary nature of nanophotonics R&D and the potential for new and unexpected developments, effective monitoring of advances in nanophotonics is expected to be difficult and complex. Therefore, comprehensive and systematic monitoring is required in order to avoid surprise from advances in the field or at least to become aware of such developments as soon as they occur. The committee found that the methodology proposed in the National Research Council report Avoiding Surprise in an Era of Global Technology Advances (NRC, 2005) for categorizing and identifying current and potential future threat environments provided a good framework for this task. To enable a more efficient technology watch and warning process for the U.S. intelligence community, the committee recommends that a data-mining tool be developed to uncover “triggers” and “observables” that will enable the U.S. national security establishment to preserve the dominance of the nation’s warfighting capability. In order to uncover pertinent information, the U.S. government could provide a mechanism to leverage critical information from the nanophotonics community. Such a secure and structured database could reveal (across all of the military services) technologies that can support multiple service needs, while also stimulating domestic nanophotonics developments. (Recommendation 4-1) The extensive investment in nanotechnology R&D by industry and academia suggests the need for the intelligence technology warning community to establish a sustained relationship with the nongovernmental nanophotonics scientific, technical, and industrial communities—that is, universities, professional societies, and trade organizations—in order to bolster its understanding and anticipation of nanophotonics technology trends. The intelligence technology warning community needs to have access to experts as nanophotonics breakthroughs occur throughout the world, particularly in countries that do not have a strong coupling to the U.S. defense community. The intelligence technology warning community should develop a sustained relationship with nanophotonics scientific and technical communities, not only within government agencies, but also in industry, academia, and technical societies, to bolster its understanding and anticipation of nanophotonics technology trends. (Recommendation 6-3) In this present early development stage of nanophotonics technology, the U.S. R&D funding agencies can accelerate the development of nanophotonics technology by funding relevant R&D as they have repeatedly done in the past for other technologies. Two past examples are Si-based microelectronics and
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Nanophotonics Accessibility and Applicability lasers. Such R&D funding action matures the technology faster so that it becomes clearer at an earlier stage how the technology can uniquely contribute to military applications, and the probability is increased that the U.S. military will be first to deploy the technology. As was the case with microelectronics and lasers, the commercial applications of nanophotonics are likely to overwhelm the military uses, requiring a healthy nanophotonics industry. Government R&D investment in nanophotonics is equally important for the emergence of this nascent industry. For the United States to maintain a leading role in the development of the interdisciplinary field of nanophotonics, a stable funding profile must be maintained. For the Department of Defense to have assured access to nanophotonics capabilities, a healthy commercial nanophotonics sector with the ability to conduct pioneering R&D is essential. Historically, feedback from basic research to applications and back to basic research has been a major factor in U.S. technological success; in an interdisciplinary field this cycle is even more vital. The committee recommends that the U.S. government funding agencies continue to support the research and development of nanophotonics technology in the United States across all phases from basic research to applications development. (Recommendation 6-2) REFERENCES JTEC (Japan Technology Evaluation Center). 1996. Optoelectronics in Japan and the United States. Baltimore, Md.: Loyola College. February. Available at http://www.wtec.org/loyola/opto/toc.htm. Accessed on January 17, 2008. NRC (National Research Council). 2005. Avoiding Surprise in an Era of Global Technology Advances. Washington, D.C.: The National Academies Press. Available at http://books.nap.edu/catalog.php?record_id=11286. Accessed on January 16, 2008.